Decoupled co-seismic deformation and stress changes during the 2021 (Mw 6.0, 6.4) Bandar Abbas earthquakes, SE-Syntaxis of Zagros, Iran; New insights into the rupture decoupling process

Decoupled co-seismic deformation and stress changes during the 2021 (Mw 6.0, 6.4) Bandar Abbas earthquakes, SE-Syntaxis of Zagros, Iran; New insights into the rupture decoupling process | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Decoupled co-seismic deformation and stress changes during the 2021 ( Mw 6.0, 6.4 ) Bandar Abbas earthquakes, SE-Syntaxis of Zagros, Iran; New insights into the rupture decoupling process Mustafa Toker, Hatice Durmuş, Murat Utkucu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2531086/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Oct, 2023 Read the published version in Environmental Earth Sciences → Version 1 posted 7 You are reading this latest preprint version Abstract The co-seismic properties of the M w 6.0 (12:07:03 UTC) and M w 6.4 (12:08:06 UTC) earthquakes that took place on 14 November 2021, Bandar Abbas Syntaxis, SE-Zagros Simply Folded Belt (SFB), Iran, are thoroughly examined. Understanding the earthquake ruptures and their relationship to the co-seismic deformations, critical to our knowledge about the earthquake source mechanisms, has provided a singular chance to interpret the details of the rupture procedure of these two interrelated earthquakes, to complement previous studies of seismicity. Here, using finite-fault source inversion, we first estimated the co-seismic source models and then the co-seismic displacements during the earthquakes, differentiated into vertical/horizontal components. We inverted the observed teleseismic broadband P -velocity waveforms of the earthquakes to simultaneously estimate the finite-fault rupture process, the slip distribution, the fault geometry and the stress changes. We found that the earthquakes were typical blind thrust-fault types along NW-SE and NE-SW striking fault lengths of ~40-50 km, widths of ~25-30 km, at a depth range of ~3-16 km and ~3-15 km, respectively, with co-seismic surface folding (~7-10 km) to NE controlled by a salt décollement layer at a depth range of ~10-12 km. We also found that the earthquakes consisted of relatively fast rupture sources (V R 3.3 km/s); an initial pure thrust faulting bilateral rupture at a depth of 12 km with a maximum slip of 30 cm and a dip angle of 32 o , which was followed by a bilateral rupture with an oblique-slip left-lateral thrust faulting at a depth of 10 km, with a maximum slip of 80 cm and a dip angle of 24 o propagated towards the NE. The joint interpretation of estimated Coulomb stress changes imparted by proposed variable slip rupture models, and the salt layer indicated that the stress increased load, triggered the fault planes of both events and influenced along-strike co-seismic strain distribution, providing evidence for the SW-NE trending activation of the stress decoupling between the ruptures, corresponding to the salt décollement. The initial pure thrust motion ruptured and mobilized the salt layer, then triggered and activated the bilateral rupture that generated the co-seismic detachment folds subparallel to the décollement. The weak salt, co-seismically ruptured and rapidly activated, compensated for co-seismic strain through lateral thickness changes from SW to NE and obliquely accommodated the folding in the shallow cover. Thus, basal ductile shear facilitated the change from pure thrust faulting in the basement to oblique thrust faulting in the cover. This finding clarifies differences in rupturing properties and deformation styles of such low-angle thrust faults. Anomalous interference patterns through superimposed fault planes of the Bandar Abbas earthquakes with the salt horizon have illuminated the rupture decoupling process and stress changes of the successive thick-/thin-skinned earthquakes, typical of the Zagros SFB. Co-seismic displacement Finite-fault source inversion Teleseismic P-waveforms Rupture process Décollement Co-seismic stress change Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction The Zagros Mountains of SW-Iran, ~ 1500 km in length and ~ 300 km wide, are seismically highly active with the most rapidly deforming fold-and-thrust structure, and are thus the most critical tectonic element of the Alpine-Himalayan belt (Nissen et al., 2011 ; Vernant et al. 2004 ) (Fig. 1 ). The range has proven to be a famous testing base for various seismic mechanistic models of fold-and-thrust deformation (Nissen et al., 2011 ) and centroid depths of high-quality earthquake mechanisms recorded in the range (at least ~ 200 focals and ~ 100 centroid depths in Nissen et al., 2011 ). Distinct sequential succession of the range stratigraphy has had a significant effect on the resulting deformation patterns, with a sedimentary cover of ~ 10–15 km thick (e.g. O’Brien 1957; James and Wynd 1965 ; Stöcklin 1968 ; Falcon 1969 ; Colman-Sadd 1978 ; Nissen et al., 2011 ) that is a combination of mechanically resilient carbonates and less resilient evaporates (Nissen et al., 2011 ). However, most of the stratigraphic and faulting studies obtained only from field geology (e.g., Molinaro et al, 2005 ) are neither supported nor validated by various types of seismological studies and have been the topic of previous significant studies being discussed for many years (e.g. Jackson and Fitch 1981 ; Berberian 1995 ; Talebian and Jackson 2004 ; Nissen et al., 2011 , 2014 ). Recognizing different types of earthquake occurrences through the stratigraphic column into the basement (or vice versa ) is particularly challenging in seismically highly active, folded-thrusted belts with detailed analyses of fault source parameters inverted from teleseismic and regional earthquake data in order to discriminate the faulting at different depths (Nissen et al., 2011 , 2014 ). The Simply Folded Belt (SFB), the outer part of the range (Fig. 1 a), offers an excellent example, comprising a substantial covering sedimentary layer (~ 10 km) together with cryptic reverse faults within which significant and damaging earthquakes have occurred (e.g., Nissen et al., 2011 , 2014 ; Talebian and Jackson, 2004 ). Previous research reported that the SFB earthquakes (Fig. 1 b) involve basement faulting due to the absence of co-seismic ruptures (Walker et al. 2005 ). However, new geodetic research has suggested that co-seismic faulting may be present in the sediments, at cover depths of ~ 4 and ~ 9 km (up to M w ~ 6.0, Nissen et al. 2007, 2010 , 2011 ; Roustaei et al. 2010 ). As revealed by Nissen et al., ( 2011 , 2014 ), well-constrained and locally recorded mainshock-aftershock sequences of observed earthquakes occur in the basement at depths of ~ 10–20 km. Therefore, these events and the mainshock faulting in the covering layer are distinct (Nissen et al., 2011 , 2014 ). For example, the SFB earthquakes (between 51.5 o and 56.7 o E and up to 29.5 o N) at Qeshm Island in 2005–2008, Fin in 2006, and Khaki-Shonbe in 2013, were shown to have occurred in covering layers (∼5–9 km) but the associated aftershocks where demonstrated to have occurred in basement layers (Barnhart et al., 2013 ; Elliott et al., 2015 ; Lohman and Barnhart, 2010 ; Nissen et al., 2010 , 2011 , 2014 ; Roustaei et al., 2010 ; Jamalreyhani et al., 2021 ). Microseismic events recorded at Qeshm Island (Nissen et al., 2010 ), Fin (Roustaei et al., 2010 ), Ghir, Khurgu (Nissen et al., 2011 ), and Khaki-Shonbe (Elliott et al., 2015 ) indicated a depth range of ~ 5–20 km (Jamalreyhani et al., 2021 ). Only some of these events were probably located at basement depths (~ 10–20 km) (e.g., Nissen et al., 2011 ; Tatar et al., 2004 ; Jamalreyhani et al., 2021 ). These previous studies conclude that many of the larger ( M w > 5) SFB earthquakes occurred in the so-called “Competent Group” of mechanically strong carbonates in the middle-to-lower sedimentary layers at depths of ∼5–10 km (Barnhart et al., 2013 ; Elliott et al., 2015 ; Lohman and Barnhart, 2010 ; Nissen et al., 2010 , 2011 , 2014 ; Roustaei et al., 2010 ). The largest recorded earthquakes in the Bandar Abbas area of the SFB, SE-Syntaxis of the Zagros have not exceeded Mw 6.7 (Fig. 1 b). Nissen et al have suggested that this is due to the Hormuz salt layer made up of weak evaporitic and/or shale horizons, which divides the seismogenic layer of the cover vertically (Nissen et al., 2010 ), preventing propagation of seismic rupturing (Nissen et al., 2010 ; Jamalreyhani et al., 2021 ). The reverse and thrust faults originate in two regions; the Hormuz salt décollement at the base of the cover (Najafi et al., 2014 ) or a secondary detachment occurring in the evaporites in the middle cover (Motamedi et al., 2012 ; Jamalreyhani et al., 2021 ). Furthermore, the salt layer also exerts control over the folds, mainly by décollement at depths of ~ 8–12 km (Allen et al., 2013 ; Motamedi et al., 2012 ; Najafi et al., 2014 ; Jamalreyhani et al., 2021 ). However, it has been shown that there is significant thrusting in the basement (Nissen et al., 2011 ; Talebian and Jackson, 2004 ). This mechanical separation is evident due to typically narrow co-seismic slip planes of finite-fault source inversion models (Elliott et al., 2015 ; Roustaei et al., 2010 ; Jamalreyhani et al., 2021 ). Previous studies suggested that the folding mechanism may have changed over time. The earlier folding was of the detachment type whereas later this manifested as thicker-skinned basement faulting and/or forced folding (Molinaro et al. 2005 ; Sherkati et al. 2005 ; Nissen et al., 2011 ). This is in agreement with an estimated cover shortening of 50–80 km (Blanc et al. 2003 ; McQuarrie 2004 ; Sherkati et al. 2006 ; Mouthereau et al. 2007 ; Nissen et al., 2011 ). This means that no plate-scale reorganization has been suggested which can explain the relation and/or discrepancy between thin- and thick-skinned deformations (e.g., Edey et al., 2020 ) observed in the SFB (Molinaro et al., 2005 ). The Bandar Abbas Syntaxis of the SFB (Fig. 1 a), where the seismicity is largely as a result of blind thrust faulting (Nissen et al., 2011 ) (Fig. 1 b), is a tectonically useful example for comparison with the two peculiar deformation styles in the cover and basement (Nissen et al., 2010 , 2014 ). Given the two phases of tectonic evolution in the Bandar Abbas region of the SFB (Molinaro et al., 2005 ) and that there has never been co-seismic surface rupturing in the Bandar Abbas Syntaxis (Molinaro et al., 2005 ), the complex mechanical relationships between buried faulting and surface folding remain controversial, as does the issue of earthquake focal depth, which may occur in the cover and/or the basement. It is therefore crucial to determine the rupture geometry, faulting pattern and surface folding induced by recent Bandar Abbas earthquakes, to complement the previous studies and to understand the relation between the expected thin- and thick-skinned deformations, which may help to resolve many unanswered seismological questions concerning events in the Bandar Abbas region of the SFB. These questions include: (1) if the basement versus the cover deformation can be decoupled in some way (Allen et al., 2013 ; Lacombe et al., 2011 ; Nilfouroushan et al., 2013 ; Edey et al., 2020 ); (2) if the Hormuz salt layer contributes to the style and distributional pattern of deformations (Authemayou et al., 2006 ; Koyi et al., 2016 ; Talbot and Alavi, 1996 ; Edey et al., 2020 ) because of the thick salt layers allowing distribution of deformation and accommodation over a wide area (Koyi et al., 2000 ; Regard et al., 2004 ); (3) what is the role of Coulomb failure stress changes in triggering and activating the thin-/thick‐skinned ruptures (e.g., Leturmy et al., 2010 ; Molinaro et al., 2005 ; Edey et al., 2020 ); and (4) whether the Bandar Abbas Syntaxis has been influenced by these two distinct deformations following ruptures of the basement and cover (e.g., fault interference patterns) through the salt layer. The two prominent earthquakes which were investigated in this research started with an initial, Mw 6.0 pure thrust faulting event (at 12:07 UTC, 27.71 o -56.07 o ) and, after a minute, Mw 6.4 oblique left-lateral thrust faulting event (at 12:08 UTC, 27.73 o -56.07 o ), in the same location at the N-part of the Bandar Abbas Syntaxis on 14 November 2021 (Fig. 1 a). Source parameters of these teleseismically recorded earthquakes and their co-seismic slip distributions using data from the Incorporated Research Institutions for Seismology (IRIS) Data Management Center propose distinct low-angle thrust earthquakes in the Bandar Abbas area (Fig. 1 b), allowing this research to re-investigate the relationship between earthquake faulting geometry, the depths at which this occurred and the resulting effects or associations with the surface. Deformation styles deduced from teleseismic waveform inversion and slip modelling of both mainshock ruptures and their focal depths provide evidence of a possible change in the deformation phases in the Bandar Abbas Syntaxis. This change, shown by finite-fault source models and centroid moment tensor (CMT) analyses, marks the transition between two successive phases. These are initial pure thrust motion and subsequent triggered and activated oblique left-lateral thrust motion, which is consistent with clockwise rotation, and NE trending horizontal σ1 axes. Accurately quantifying and representing the focal depths and our preferred model co-seismic slip orientations of both earthquakes may help to resolve the questions concerning the mechanical, structural and seismogenic mechanisms occurring in the Zagros orogeny. 2. Tectonic Context The Zagros Mountain range (Fig. 1 a) is one of the world's most active continental seismic belts, study of which has resulted in much greater understanding of the mechanisms of fold-and-thrust earthquake, salt tectonics (Nissen et al., 2011 , 2014 ) and related halokinesis. The Zagros range marks the leading edge of the collision between the Arabian and Eurasian continental plates (Fig. 1 a), which may have begun in the late Eocene or early Oligocene (Allen and Armstrong, 2008 ; Mouthereau et al., 2012 ; McQuarrie and van Hinsbergen, 2013 ; Nissen et al., 2014 ). Current GPS measurements show that N-S shortening along the range vary from ~ 9 mm yr − 1 in the SE to ~ 4 mm yr − 1 in the NW (Vernant et al. 2004 ; Walpersdorf et al. 2006 ; Nissen et al., 2014 ). However, only a small fraction of the convergence is directly attributable to earthquake moments (Jackson and McKenzie 1988 ; Masson et al. 2005 ; Nissen et al., 2011 ). The 100–200 km wide SFB, which comprises the SSE-part of the Zagros (Hessami et al., 2006 ; Walpersdorf et al., 2006 ), rises from sea level at the SW end to around 1500 metres in height in the NE (Fig. 1 a) and exposes the Hormuz salt plugs (Nissen et al., 2011 ). The SFB is separated from the High Zagros (HZ) by the High Zagros Fault (HZF), a major NE-dipping thrust (Fig. 1 a) (Nissen et al., 2011 ). The SFB is further subdivided into two lobate salients; high relief Lurestan Arc and Fars Arc, which are separated by a recess with relatively low-lying topography of the Dezful Embayment (Fig. 1 a) (Nissen et al., 2011 ). The HZ includes Mesozoic and Palaeozoic sediments with ophiolites (Stoneley 1990 ) and the NW-striking thrust/reverse faults are exposed at the surface; the MZT (Main Zagros Thrust) and the HZF (Fig. 1 a) (Nissen et al., 2011 ). The MZT marks the meeting of Arabian and central Iranian structures (Alavi 2007 ) and is coincident with the right-lateral Main Recent Fault (MRF) (Walpersdorf et al. 2006 ; Nissen et al., 2011 ). The HZF was the location of the only known example of reverse faulting co-seismic surface rupture within the boundary with the SFB, on the 6 November 1990 during the Furg earthquake ( M w 6.5) in the far SE of the SFB (Walker et al. 2005 ; Nissen et al., 2011 ) where the HZF is blind and includes gentle folding, typical of the SFB (Fig. 1 a) (Nissen et al., 2011 ). Major changes in both the stratigraphy and elevation across some folds of the SFB are due to major N-dipping basement faults, termed “master blind thrusts” (Fig. 1 a) (Berberian, 1995 ; Nissen et al., 2011 , 2014 ), one of which is the Mountain Front Fault (MFF). The MFF accommodates ~ 75% shortening (Walpersdorf et al., 2006 ) has a throw of ~ 2–4 km, and up to ~ 6 km in the SFB (Blanc et al. 2003 ; Molinaro et al. 2005 ; Emami et al. 2010 ; Berberian 1995 ; Sherkati et al. 2006 ; Nissen et al., 2011 ). Many earthquakes that have happened in the SFB have originated on the MFF (Jackson and McKenzie, 1988 ; Ni and Barazangi, 1986 ; Berberian, 1995 ; Mouthereau et al., 2007 ) and have a NE-dipping attitude (Tatar et al., 2003; Hatzfeld and Molnar, 2010 ; Nissen et al., 2011 ). The HZF and MFF, with vertical displacement of up to ~ 6 km (Berberian 1995 ; Molinaro et al., 2005 ), are highly active beneath the sedimentary cover (Molinaro et al., 2005 ), have been described as major segmented reverse faults, and have seismogenic and morphologic characteristics evident within the SFB (Berberian, 1995 ; Molinaro et al., 2005 ; Nissen et al., 2011 , 2014 ). The HZF contributes locally to strain via oblique convergence (e.g. Lettis and Hanson, 1991 ; Malekzade et al., 2007), while the MFF exerts a major influence on the flexural basin following collision (Hessami et al., 2001 b; Sepehr and Cosgrove, 2005 ). The Bandar Abbas Syntaxis (Fig. 1 a) includes the far E-folds and thrusts of the Fars Arc (Molinaro et al., 2004 , 2005 ) and may be considered to consist of two subdomains, the southerly SFB and the northerly HZB (High Zagros Belt), separated by the HZF (Molinaro et al., 2005 ). 2.1. Mechanical stratigraphy of the SFB in the Bandar Abbas Syntaxis The topographic slope across the SFB (Fig. 1 a) varies from < 1 o up to 2 o across the ~ 100 km-wide strip separating the Dezful Embayment from the HZF (McQuarrie 2004 ), corresponding to a stepped surface, rather than a simple, planar one (Mouthereau et al. 2007 ; Nissen et al., 2011 ). The SFB contains thick, folded Phanerozoic sediments, which are detached from underlying basement rocks by the Precambrian Hormuz Formation varying in dimension from 1–4 km (Jahani et al. 2007 ). The Hormuz Formation consists of multiple evaporitic and non-evaporitic sediments, evident at the surface as numerous active salt diapirs (Gansser, 1960 ; Kent, 1970 , 1979 ; Ala, 1974 ; Edgell, 1996 ; Jahani et al., 2007 ; Barnhart and Lohman, 2012 ; Nissen et al., 2014 ). The Hormuz salt is thus brought to the surface in scattered diapirs (e.g. O’Brien 1957; Nissen et al., 2014 ). Furthermore, more robust sediments, dismantled by salt diapirism and folding, within large and intact rafts of between 2–4 km diameters may be transported to the surface by salt flow (Nissen et al., 2011 , 2014 ). The Lower Mobile Group, comprising late Hormuz evaporites, rests directly on the basement (see Nissen et al., 2014 for the term “basement”) and is the main regional décollement level for most of the larger folds within the SFB (Nissen et al., 2014 ), including detachment and faulted detachment folds, imbrications and duplex structures (Molinaro et al., 2005 ; Nissen et al., 2014 ). The lower-middle cover, labelled the “Competent Group” by O'Brien in 1957, is a structurally competent layer (Nissen et al., 2014 ; Molinaro et al., 2005 ). The Competent Group comprises a 4000–5000 metre thick sequence and is the main unit underlying the large wavelength anticlines in the SFB, corresponding to an important regional décollement horizon (Nissen et al., 2014 ; Molinaro et al., 2005 ). The Upper Mobile Group forms the major roof décollement and largely decouples deformation below and above underlying structures (Nissen et al., 2014 ; Molinaro et al., 2005 ). Faults propagating upward tend to dissipate displacement within the Upper Mobile Group (Molinaro et al., 2005 ). A 2000–4000 metre thick sequence forms this “Incompetent Group” (Molinaro et al., 2005 ). This Incompetent Group includes syntectonic sedimentation in the higher regions of the sequence (Hessami et al., 2001 b) and small-scale thrusting and thrust-related folds extending into the sediments (Molinaro et al., 2005 ). These groups thus comprise a total of ~ 10–15 km-Phanerozoic stratigraphic thickness (James and Wynd, 1965 ; Molinaro et al., 2004 ; Sherkati et al., 2005 ; Carruba et al., 2006 ; Casciello et al., 2009 ; Verges et al., 2011 ; O'Brien, 1957 ). The depth to basement across the SFB has been shown to be within the range 9–13 km, using cross-sections that include both structural thickening and erosion (Nissen et al., 2010 , 2011 ). This range estimate is further suggested by local microseismicity surveys that have shown an increase in body-wave velocities below 10–12 km (Hatzfeld et al., 2003 ; Tatar et al., 2004 ; Nissen et al., 2010 ; Roustaei et al., 2010 ; Nissen et al., 2011 ; Yaminifard et al., 2012 a, b). Others consider the basement depth to be ~ 8–12 km (e.g., Allen et al., 2013 ; Najafi et al., 2014 ; Jamalreyhani et al., 2021 ). Based on long-wavelength signals, aeromagnetic data (Kugler 1973 ; Morris 1977 ) has suggested basement depths of 4–18 km (Talebian 2003 ; Nissen et al., 2011 ). Other studies have estimated the total sedimentary thicknesses of the SFB to be ~ 14 km in the NW, ~ 12 km in the central Fars Arc and ~ 10 km in the far SE (Fig. 1 a) (e.g. Colman-Sadd 1978 ; Molinaro et al. 2005 ; Sherkati et al. 2005 ; Casciello et al. 2009 ; Nissen et al., 2011 , 2014 ). The Phanerozoic cover thickness is estimated at 14 (± 2) km, consistent with mean P-wave velocities of 4.7–5.7 km/s (Nissen et al., 2014 ). 2.2. Seismic structure of the Bandar Abbas Syntaxis In the SFB, seismicity is dominated by blind thrust faulting (Fig. 1 b), rarely associated with surface rupturing (Walker et al. 2005 ; Nissen et al., 2011 ) so that surface shortening is facilitated by a series of anticlines and synclines (Fig. 1 a) (Nissen et al., 2011 ). The mechanism of folding within the SFB depends on either buried faulting or lateral variations in the stratigraphy, or both (Nissen et al., 2011 , 2014 ). The short-wavelength topography and surface structure of the SFB were originally thought to be detachment folds, formed by buckling of the cover along décollements within the sedimentary cover (e.g. Falcon 1969 ; Colman-Sadd 1978 ; Jackson 1980 ; Nissen et al., 2011 , 2014 ). A possible cause of this was the shallower décollements within the middle sedimentary cover also resulting in surface folding (e.g. Sherkati et al., 2005 ; Carruba et al., 2006 ; Sepehr et al., 2006 ; Vergés et al., 2011; Nissen et al., 2011 , 2014 ). However, this would need multiple décollements to yield the observed spacing of folds and also the preponderance of folding compared to faulting (Yamato et al., 2011 ; Nissen et al., 2011 , 2014 ). Detachment originating in the Hormuz salt has been suggested to allow fault propagation folding over the steep reverse faults which then branch upwards into the cover (McQuarrie, 2004 ; Nissen et al., 2011 , 2014 ). An additional complicating factor is the Hormuz diapirism. This affects the location of folding and faulting, particularly in the Bandar Abbas area where salt plugs are most prevalent (Jahani et al., 2009 ; Nissen et al., 2014 ). It has been suggested that the sedimentary cover is completely aseismic and faulting only occurs in the basement (e.g. Mouthereau et al. 2007 ; Nissen et al., 2011 , 2014 ). The N-dipping blind thrusts form a focus either in the lower reaches of the sedimentary cover (McQuarrie 2004 ; Alavi 2007 ; Nissen et al., 2011 , 2014 ) or in the underlying basement, but may penetrate the Hormuz salt to pass into the sediments (Berberian 1995 ; Nissen et al., 2011 , 2014 ). The seismicity of the Bandar Abbas Syntaxis, the strongest in the SFB (Fig. 1 b), is concentrated at depths of 8–12 km (Jackson and Fitch, 1981 ; Berberian, 1995 ; Talebian and Jackson, 2004 ) yielding the lowest estimate of depth to basement of ~ 8 km (Nissen et al., 2011 , 2014 ). Between depths of 8 and 17 km, reverse focal mechanisms occur (Talebian and Jackson, 2004 ) which define clear alignments, possibly associated with the MFF and HZF basement faults (Fig. 1 a) (Berberian, 1995 ; Molinaro et al., 2005 ; Nissen et al., 2011 ). It has been proposed that the ruptures in the basement correspond with the MFF and the HZF (Berberian, 1995 ; Molinaro et al., 2005 ) with focal depths of 10–11 km for the MFF and 7–8 km for the HZF (Talebian and Jackson, 2004 ; Molinaro et al., 2005 ). In the SFB earthquakes appear to concentrate in the basement zones, as there is no evidence of co-seismic, primary surface rupturing (Nissen et al., 2014 ). The presence of major basement faults and abrupt changes in stratigraphic level across certain anticlines of the order of magnitude of kilometers (Berberian, 1995 ), and data from local microseismic surveys all point to events occurring at basement depths (Hatzfeld et al., 2003 ; Tatar et al., 2004 ; Nissen et al., 2010 ; Roustaei et al., 2010 ; Nissen et al., 2011 ; Yaminifard et al., 2012 a, b). Basement faults appear to have developed relatively late in the Pliocene, following the earlier thin-skinned phase of deformation (Molinaro et al., 2005 ; Sherkati et al., 2005 ; Nissen et al., 2014 ). However, there is considerable evidence that centroid depths of large earthquakes appear to predominantly (~ 75%) occur in at depths of 4–10 km, suggesting ruptures occurring within the “Competent Group” of sediments (Jackson and Fitch, 1981 ; Kadinsky-Cade and Barazangi, 1982 ; Jackson and McKenzie, 1984 ; Ni and Barazangi, 1986 ; Baker et al., 1993 ; Priestley et al., 1994 ; Maggi et al., 2000 ; Talebian and Jackson, 2004 ; Adams et al., 2009 ; Nissen et al., 2011 , Nissen et al., 2014 ). 3. Data And Methods In this study, we used teleseismically recorded broadband P-velocity waveforms, accessed through the IRIS Data Management Centre, to perform finite fault source inversion and to constrain co-seismic slip distributions of the 2021 Bandar Abbas earthquakes using 27 stations with epicentral distances between 32° and 87°. Time alignment is critical for finite-fault inversion modeling, which uses more P than SH waveforms. This is because P-wave onsets are generally much easier to identify with confidence compared to those of SH waves (Ammon et al., 2008 ). The P waveforms data band-pass filtered with corner frequencies (0.01 to 0.5 Hz) were resampled with a time interval of 0.50 s after being corrected for instrumental responses. The first 40 s of the waveform was modeled. In order to avoid deep-seated velocity distortion and/or boundary layer diffraction in the waveforms, the epicentral distances selected for our analysis were chosen in the range from ~ 30° to ~ 90°. Parameters selected are summarized in Table 1 . The one-dimensional (1-D) initial crustal velocity model, as compiled from Nissen et al., ( 2010 ) and Manaman and Shomali, ( 2010 ), used in the inversion is provided in Table 2 . Table 1 Parameters of teleseismic data processed for the 2021 Bandar Abbas earthquakes. Parameters Earthquake 1 (Eq. 1) Earthquake 2 (Eq. 2) Number of stations 24 25 Waveforms P velocity waveforms P velocity waveforms Teleseismic distance 32° and 85° 32° and 87° Sampling interval 0.50 s 0.50 s Filter and corner frequencies Band-pass filter (0.01 to 0.5 Hz) Band-pass filter (0.01 to 0.5 Hz) The first 40 s of the waveform The first 40 s of the waveform Table 2 1-D initial crustal velocity model structure (compiled from Nissen et al., 2010 , and Manaman and Shomali, 2010 ) used for the inversion in this study (also see Utkucu et al., 2018 for the model). Thick. (km) V P (km/s) V S (km/s) ρ (gr/cm 3 ) 8.0 5.50 3.00 2.70 4.0 5.90 3.20 2.50 33.0 6.20 3.40 2.80 - 8.10 4.40 3.00 3.1. Finite-fault source inversion Following the same methodology and inversion procedure detailed in the co-seismic slip studies of Utkucu et al., ( 2018 ) and Durmuş and Utkucu, ( 2021 ), we performed a finite-fault source inversion method, first described by Hartzell and Heaton, ( 1983 ), to constrain the co-seismic slip distributions across the fault plane models of the first and second mainshocks (Eq. 1 and Eq. 2) regarding the previous fault source models (Utkucu et al., 2018 ; Durmuş and Utkucu, 2021 ). The fault planes, divided into subfaults, together with focal depths and source parameters, were modelled in the source areas of both mainshocks. We estimated the point source responses using the generalized ray theory of Langston and Helmberger, ( 1975 ). Using a point source, although an approximation, has been demonstrated to be reliable for shallow slip associated with low-angle thrusts (Ammon et al., 2008 ). The inversion, based on point-source strength, converts to slip, as each point source is assumed to represent a sub-event with size equal to the distance between sources. In order to simulate radial propagation of the high velocity ruptures, point sources are equally spaced across the fault planes. In order to image sub-fault synthetic seismograms (Green’s functions) for each station used, the point source responses are summed with appropriate lagging time corresponding the rupture delay. Then, we convolved the synthetic seismograms with an attenuation operator ( t* ) as a function of frequency, in this case 0.7 s for P -wave attenuation (Choy and Cormier, 1986 ). During inversion, our time window approach allowed estimation of variable slip rise time of each window, represented by isosceles triangles, and the rupture velocity over the model faults, by performing these calculations with an efficient linear inversion based algorithm (due to heterogeneous rupture propagation by Hartzell and Heaton 1983 ; Mendoza 1995 ; Wald and Thomas 1994 ; Ammon et al., 2008 ). The method allows each sub-fault to rupture for a specified time interval with a source time function (STF) shape (Ammon et al., 2008 ). Thus, we modelled varying velocities of the rupture within an assigned range across the fault plane, depending on the earliest possible rupture time of each point source (high initial velocity of the rupture). The equation expressed by the observed and synthetic waveforms is written as Ax = b , where A and b are matrixes defined by synthetic and observed waveforms, respectively and x is a matrix defined by slip weights for each subfault. The values of x are estimated using a Householder least squares inversion technique (Lawson and Hanson, 1974 ) requiring that x and/or solution vector elements are ≥ 0. Lastly, in order to image a spatially smooth slip model with minimum seismic moment (Hartzell and Heaton, 1983 ; Wald and Thomas, 1994 ), we further constrained the solution vector using spatial smoothing through moment minimization. We successively perturbed the rupture models in a search for better-fitting models, tried several initial inversion trials for both the mainshocks to properly constrain fault model dimensions and positions with respect to the focal depths. This finally led to identifying a good fit of the data with fixed-rake parameterization. Before selecting the fault dimensions for our models, we also thoroughly explored fault width and length. The parameters used in the finite-fault source modeling of the first (Eq. 1) and the second (Eq. 2) mainshocks are given in Table 3 . Parameters also included for Eq. 1, fault source parameters of strike 114 o , dip 32 o , rake 91 o and centroid depth of 12 km, with fault and sub-fault dimensions (40 x 25 km and 5 x 5 km, respectively) with a total of 40 sub-faults. Similarly, for Eq. 2 these were fault source parameters of strike 49 o , dip 24 o , rake 27 o and centroid depth of 10 km, with fault and sub-fault dimensions (50 x 30 km and 5 x 5 km, respectively) with a total of 60 sub-faults, considering a rupture velocity ( V R ) of 3.3 km/s, slip rise-fall time of 0.5–0.5 s and 5 − 0 of TW-window lag time. Table 3 Parameterization used in the finite-fault source inversion modeling for the 2021 Bandar Abbas earthquakes. Parameters Earthquake 1 (Eq. 1) Earthquake 2 (Eq. 2) Lat.( o ) - Long. ( o ) 27.71–56.07 27.73–56.07 Point-Source (strike/dip/rake) (s 1 -s 2 )/(s 1 -s 2 )/(s 1 -s 2 ) 114 o /32 o /91 o 49 o /25 o , 24 o /17 o , 27 o /168 o Point-Source (Mo x 10 25 Dyn.cm) 1.38 3.80–2.15 Finite-Source (strike/dip/rake) 114°/32°/91° 49°/24°/27° Finite-Source (Mo x 10 25 Dyn.cm) 1.8 6.9 Model fault dimensions (km x km) 40 x 25 50 x 30 Subfault dimensions (km x km) 5 x 5 5 x 5 Subfault numbers 40 60 Rupture velocity (V R , km/s) 3.3 3.3 Rise-fall time (s) (isosceles triangle) 0.5–0.5 0.5–0.5 TW-window lag time 5 − 0 5 − 0 Hypocentral depth (km) 12.0 10.0 Top-bottom depth of fault (km) 3.0–16.25 3.0–15.20 Distributional patterns of co-seismic slip models estimated for the 2021 Bandar Abbas mainshocks are given in Figs. 2 a and 3 a, while their corresponding synthetic-observed waveform comparisons are presented in Figs. 2 b, 2 c and 3 b, 3 c. Vertical components of co-seismic slip distributions of both mainshocks are shown in Fig. 4 . Their horizontal components with corresponding cross-sectional profiles projected on slip models of both events are shown in Fig. 5 . NE-SW striking cross-sectional profile projected on horizontal displacements of both mainshock slips, combined with vertical displacements, shown in Fig. 4 , is jointly interpreted and displayed in Fig. 6 . The slip distribution models indicate bilaterally developed low-angle pure thrust faulting (Eq. 1) and oblique left-lateral thrust faulting (Eq. 2). Both events are heterogeneously ruptured in centroid depths of 12 − 10 km with conjugate trends to NW-SE and NE-SW, in maximum fault lengths of ~ 40–50 km with maximum fault slips of ~ 30–80 cm, respectively. 3.2. Coulomb failure stress changes In this section, Coulomb failure stress changes due to the Bandar Abbas mainshocks are computed to estimate co-seismic stress variations and interactions (Coulomb 3.3 software, Lin and Stein 2004; Toda et al. 2005) between Eq. 1 and Eq. 2 using the slip distribution models (Figs. 2 a and 3 a) created in this study. The Coulomb failure stress change (Δσ f ) can be defined as: Δσ f = Δτ + µ Δσ n (1) where changes in the shear and the normal stresses are represented by (Δτ) and (Δσ n ), respectively (Harris 1998 ; King et al. 1994 ). The value of the apparent coefficient of friction (µ) includes the effect of varying pore fluid pressure ranging from 0.2 to 0.8. We assumed source fault ruptures as rectangular dislocation surfaces, computed after Okada, ( 1992 ), in an elastic half-space with Young’s modulus of 8×10 5 bar, Poisson’s ratio of 0.25 and friction of 0.4. We computed the co-seismic stress changes over the optimally oriented strike-slip fault planes along with the variable slip models using source parameters (strike, dip, rake, fault dimensions) of both mainshocks, given in Figs. 2 a and 3 a. Images of calculated co-seismic stress changes are computed at a depth of 10 km, together with ~ 300 aftershocks ( M ≥ 2.5 ) observed during the subsequent two months and definition of principal stress axes orientations for the regional stress field, are shown in Fig. 7 . The azimuth and plunge pairs for the three principal stress axes (σ1, σ2, σ3) are, as compiled from regional stress (world stress map), (333°, 6°), (218°, 75°), (64°, 13°), respectively. Figure 7 represents co-seismic stress changes of both mainshocks calculated over optimally oriented strike-slip faults. Figure 7 a illustrates the stress changes imparted by Eq. 1 over its fault plane, while Fig. 7 b shows the stress changes imparted by Eq. 2 over superimposed fault planes of both Eq. 1 and Eq. 2. Figure 8 shows cross-sectional NW-SE and NE-SW striking A-B and C-D profiles, respectively, projected on the fault plane of Eq. 1. Figure 9 shows cross-sectional NE-SW striking A-B, C-D, and E-F profiles parallel to the fault plane and the NW-SE striking G-H profile projected on the fault plane of Eq. 2. Most of the located aftershocks, which are densely consolidated in a depth range of ~ 5–20 km, are observable on- and end-fault areas of increased co-seismic stress through cross-sections of Eq. 1 and Eq. 2. 4. Interpretation And Discussion 4.1. Co-seismic slip distributions Finite fault-source inversions of azimuthally distributed teleseismic P waveforms and body wave effective source time functions (STFs) yielded co-seismic slip distributions on low-angle thrust faulting geometries. Our preferred model for the 2021 Bandar Abbas thrust faulting event (Eq. 1) has a fault orientation of strike 114 o and dip 32 o , with nearly pure thrust motion with a rake of 91 o . For the oblique, left-lateral thrust faulting event (Eq. 2), our rupture model geometry has a strike of 49 o , a dip of 24 o , and a rake of 27 o . The major ruptures cover faulted areas of 40 x 25 km (Eqs. 1) and 50 x 30 km (Eq. 2) (Table 3 ). The co-seismic slip, confined to a depth range of 3–16 km, suggests mostly a bilateral rupture propagation pattern towards NE (Fig. 2 a). Our source parameters obtained from the inversion are fairly consistent with the results of the Geological Survey of the United States (USGS) which estimated for Eq. 1, strike 91 o , dip 27 o , rake 91 o (40 x 25 km with 40 sub-faults) and for Eq. 2, strike 41 o , dip 12 o , rake 22 o (50 x 30 km with 60 sub-faults). The distribution pattern of the aftershocks also favors the shallow dipping planes as the fault planes of our models; the SW-dipping plane of Eq. 1 aligns better with the aftershock distribution, together with the rupture on a rotated SE-dipping plane of Eq. 2. Our seismic moment was 1.8 x 10 25 (dyn.cm) for Eq. 1, equivalent to a moment magnitude of Mw 6.13, while the seismic moment was 6.9 x 10 25 (dyn.cm) for Eq. 2, equivalent to a moment magnitude of Mw 6.52. Seismic moments of Eq. 1 and Eq. 2 as point sources were 1.38 x 10 25 (dyn.cm) and 2.15–3.8 x 10 25 (dyn.cm), respectively. Due to a relatively fast V R of 3.3 km/s constrained by body-wave directivity, the main rupture lasted about ~ 5 s for Eq. 1 and ~ 10 s for Eq. 2, with a spatially and poorly resolved weak radiation pattern lasting for ~ 15 s (Eq. 2) (Figs. 2 and 3 ). Several asperities observed from the slip distribution models range from 10 to 30 cm for Eqs. 1 and 10 to 80 cm for Eq. 2 on the fault planes (Figs. 2 and 3 ). The slip model obtained for Eq. 1 suggested a relatively heterogeneous slip pattern with two distinct asperities. These were dominance of a large asperity (to SE) with a peak slip of ~ 30 cm and a small asperity (to NW) with a peak slip of ~ 10 cm located just updip (~ 8 km) of the focal depth (Fig. 2 a). The slip model obtained for Eq. 2 suggested a more heterogeneous slip pattern with five distinct asperities, which were dominance of a large asperity with a peak slip of ~ 80 cm located just updip (~ 8 km) of the focal depth and four small asperities (to NE and to SW) with a peak slip of ~ 10–20 cm, two of which were located updip ( < ~ 4 km) and the other two located downdip (~ 10 km) of the focal depth (Fig. 3 a). Distributional patterns of co-seismic slip models indicate that the bilateral rupture sources of both mainshocks occurred on low-angle, blinded, pure thrust/oblique left-lateral thrust structures along fault lengths of 40–50 km (max) in the depth range of 3–16 km (max). 4.2. Co-seismic off fault deformation Figure 4 illustrates the maximum vertical displacement gradient, marked by the sharp contact between blue to red patterns, which are characterized by peculiar circular shapes on surface projections of the co-seismic slips of Eq. 1 and Eq. 2 (Figs. 2 a and 3 a). Figure 4 a shows a weak downlift (-1 cm) and uplift (1 cm) of Eq. 1, which also corresponds to the area of maximum horizontal displacement (~ 5–15 cm) and (~ 15–30 cm), respectively (Fig. 5 a). In Eq. 1, off fault deformation at a depth range of 3–16 km was relatively less evident and locally interrupted to the NE by a gentle horizontal gradient (Figs. 5 a-e). Figure 4 b shows a gentler increase of the downlift (up to -3 cm) in the central part of the subsiding area and a little more uplift (2 cm) of Eq. 2, also corresponding to the area of maximum horizontal displacement (~ 10–80 cm) (Fig. 5 b). In Eq. 2, off fault deformation was strongly evident by a long wavelength curvature (~ 50 km in length) and well-localized, small vertical and sharp horizontal displacements toward the NE (Figs. 5 b-e). This is best traced through the NE-SW striking cross-sectional profile shown in Fig. 5 e, which is interpreted in detail and shown in Fig. 6 . In Fig. 6 , shallow, off-fault deformation at a depth range of 7–10 km is characterized by various components of sharp horizontal and small vertical displacements; along the profile striking from SW to NE, a flexural (down) slip of ~ 20 cm (max), detachment (strike) slip of ~ 25 cm (max), fold (up) slip of ~ 15 cm (max), thrust (up) slip of ~ 10 cm (max) and fold (up) slip of ~ 5 cm (max) are observed. In Fig. 6 , in the SW, the hanging wall block of Eq. 2 shows a typical curvature of long wavelength deformation, characterized by downthrow and/or flexural bending through the décollement surface toward the fault and a weak bulge up to 2 cm along its hinge zone. To the NE, the displacement gradient decreased (from ~ 20–25 cm to ~ 5 cm) and a weaker uplift (1 cm) formed, leading to the loss of the curvature further to the NE at a depth range of ~ 5–7 km; the long wavelength hanging wall deformation over a length of ~ 50 km decreased where the fault displacement was lower (and vice versa ). Shallow, off-fault deformation, characterized by a downthrow movement of the hanging wall following a gradual curvature toward the fault to accommodate on fault low-angle movement (décollement), implies long wavelength-low amplitude co-seismic surface folding (2 cm max) and subsidence (-3 cm max) with a maximum horizontal displacement (80 cm) along the length of ~ 50 km (Fig. 6 ). 4.3. Co-seismic stress changes The co-seismic stress changes shown in Fig. 7 a indicate that most of the rupture plane of Eq. 1 was loaded by high stress interaction at a depth of 10 km and most of the aftershocks fell into the stress increase area in SE. The stress changes imparted by Eq. 1 loaded and activated the NE-SW striking fault plane of Eq. 2 and aftershock cluster in SE. Meanwhile, the W-, E- and S-parts of both fault planes were unloaded and deactivated, generating stress shadow zones, where some aftershocks were observable. In Fig. 7 b, the hypocentres of Eq. 1 and Eq. 2 and most of the aftershocks remain in the areas of stress increase. The aftershocks that covered the SE part mostly showed positive correlation with the stress changes and completely fell into the stress enhanced area, while the aftershocks in the S-part remained in the stress decreased area (Fig. 7 b). As seen in Figs. 7 a and 7 b, the rupture geometry of the fault plane and smaller stress interaction (0.1 bar) imposed by Eq. 1 loaded and triggered the NE-SW striking fault plane of Eq. 2, which in turn unloaded and deactivated (-0.1 bar) W-, E- and S-parts of both fault planes. In both rupture patterns associated with high-low stress periods at a depth of 10 km, the hypocentral sections of Eq. 1 and Eq. 2 remained in a high stress area. An area of increased stress pattern, striking NE-SW subparallel to the fault plane of Eq. 2, implies strong successive “along-strike” activation of the low-angle thrust faulting to NE and to SW on the co-seismic stress transfer. This is best explained by cross-sectional depth profiles of co-seismic stress interactions between Eq. 1 and Eq. 2, as shown in Figs. 8 and 9 . In Fig. 8 , at sections below and above 10 km depth, there are distinct off fault areas of increased stress, while end fault areas of decreased stress are also observable, indicating that shallow and deep sections of the fault plane of Eq. 1 with on fault events activated “off fault triggering”, up to 0.1 bar. Figure 9 shows, along the A-B profile, both shallow ( 10 km) areas of increased stress propagating toward NE, which suggests stress coupling in the NE with a shallow area of increased stress to the SW. In Fig. 9 , the C-D profile, projected on hypocentral sections of both fault planes, shows shallow-to-deep and deep-to-shallow areas of high-to-low and low-to-high stress toward NE and SW, which suggests strong decoupling of the co-seismic stress transfer. In Fig. 9 , the E-F profile shows shallow and deep areas of increased stress propagating toward SW, which suggests stress coupling in SW with shallow-to-deep and deep-to-shallow areas of low-to-high and high-to-low stress toward the NE, suggestive of stress decoupling. The G-H profile shows shallow and deep areas of high-to-low and low-to-high stress propagating toward SE and NW, which again suggests stress coupling (Fig. 9 ). In each case of the profiles shown in Fig. 9 , the source fault planes of Eq. 1 and Eq. 2 remain highly loaded by an increase of stress that indicates “on-fault triggering”, consistent with “off-fault triggering” shown in Fig. 8 . Deeper areas (> 10 km) of increased stress show stress triggering and seismic activation (A-B, C-D, E-F profiles), but shallower areas (< 10 km) of decreased stress show stress shadowing and seismic deactivation (C-D, E-F profiles) toward NE. This implies the SW-NE striking on-fault/off-fault stress triggering through both shallow and deeper areas, suggesting coupled and decoupled interaction of the co-seismic stress variations through both source fault planes of Eq. 1 and Eq. 2. We propose that the coupling-decoupling complexity of co-seismic stress cycles along both fault planes is caused by superimposed and buried low-angle rupture sources (Fig. 6 ). The co-seismic slip led to a decrease of the normal stress and an increase of the shear stress on the fault plane, with a low dip angle that makes low frictional strength slip (e.g., Duan et al., 2022 ). The low-angle rupture sources appear to be consistent with segmental fault geometries (e.g., flat-ramp-flat geometry) with fault surfaces inclined at varying angles of 4 o -35 o (Chen et al., 2020 ; Duan et al., 2022 ). 4.4. Centroid depth structure of earthquake faulting phenomena in SFB We have presented the following: (a) the co-seismic slip distribution models consist of relatively fast rupture sources of Eq 1 and Eq 2 (V R , 3.3 km/s) that occurred on low-angle, blind, pure thrust (NW-SE)/oblique left-lateral thrust (NE-SW) faults with centroid depths of 12-10 km, respectively, along a fault length of 50 km (max) at a depth range of 3-16 km (max) (Figs. 2, 3 and 6); (b) the co-seismic off-fault deformation at a depth range of 7-10 km (max) implies long wavelength-low amplitude co-seismic surface folding, with a slip of 80 cm (max) along a length of ~50 km (Figs. 4-6); and (c) the co-seismic stress changes significantly load and activate the source fault planes of Eq 1 and Eq 2 and greatly influence along-strike strain distribution to NE (Fig. 7). The on-fault/off-fault triggering that extended from SW to NE through shallow ( 10 km) sections (Figs. 8 and 9 ) suggested coupled and decoupled interaction of the co-seismic stress variations through both source fault planes of Eq. 1 and Eq. 2 toward the NE. Coulomb failure stress coupling and decoupling phases through various depths are interpreted as indicating coupled and decoupled co-seismic deformations. In the following sections, we briefly review the major results of previous research and discuss the key implications of our study, with specific reference to: (i) the relationship between the 2005 Qeshm, 2006 Fin and the Bandar Abbas earthquakes; (ii) the presence of the co-seismic surface folding; (iii) decoupled seismic deformation and its implications for thick-skinned versus thin-skinned deformation, together with rapid and oblique propagation of co-seismic deformations driven by a triggered and activated basal décollement salt horizon over a wide area; and (iv) tectonic significance of the rupture decoupling process. Centroid depths of 10–12 km for the Bandar Abbas mainshocks suggest ruptures in the basement and/or the lower part of the sedimentary cover (e.g., Nissen et al., 2011 , 2014 ), and co-seismic slips are unlikely to have affected the surface (Figs. 2 a and 3 a). Similarly, the 2005 Qeshm and 2006 Fin earthquakes occurred in the sedimentary cover, rather than the basement, but their centroid depths appear to be near to the depths where the cover and basement meet (Nissen et al., 2011 , 2014 ). In the SFB, given the 30-60 o dips of most of the reverse faulting events, most of the earthquakes not only rupture the sedimentary cover, but also nucleate within it (Nissen et al., 2011 , 2014 ). Thus, the Qeshm, Fin and Bandar Abbas earthquakes may be the best examples of this phenomenon. Low-angle thrusting, consistent with the source mechanisms of the Bandar Abbas mainshocks, seems to have had a major effect in some areas in the SE-Zagros (Nissen et al., 2011 ). The fault-plane solutions of regional earthquakes suggest several low-angle thrust faulting mechanisms, consistent with teleseismic focal mechanisms (Nissen et al., 2011 ) with optimal accuracy at depths of 10–20 km and an estimated centroid depth error of ± 2 km (Nissen et al., 2011 ), while reverse faulting earthquakes have centroid depths of 4–20 km (Nissen et al., 2011 ). Scattered, low-angle thrusts occurred at centroid depths of 5, 14 and 17 km in and around the Dezful Embayment and the deeper cut-off suggested by microseismicity is largely at 20 km or more (Nissen et al., 2011 ). At Fin there have been many events at 20–30 km depth, while well-resolved hypocentral depths were as much as 35–40 km at Minab (Nissen et al., 2011 ). Earthquakes occurring at > 20–23 km and up to around 28 km are consistent with slip on shallow, N-dipping planes where the Arabian basement thrusts under the Eurasian plate (Nissen et al., 2011 ). 4.4.1. The 2005 Qeshm and 2006 Fin earthquakes Gentle symmetrical folds are usually associated with detachment folding. The Qeshm and Fin earthquakes occurred in such an area (Nissen et al., 2011 ). Basement faulting may have given rise to the few earthquakes with centroid depths of > 15 km (e.g. Jackson 1980 ; Maggi et al. 2000 ; Talebian and Jackson, 2004 ; Hatzfeld et al. 2010 ; Nissen et al., 2011 ). This suggests a seismogenic layer of ∼20 km thick, consistent with ~ 25–30 km at Kermanshah, Fin and Khurgu (Nissen et al., 2011 ). The Qeshm mainshock-aftershock sequence The Qeshm Mw 6.0 reverse faulting earthquake at 10:22 UTC on 27 November 2005 had no associated surface rupture (Nissen et al., 2007b ). The centroid depth range was estimated at 6–10 km (Nissen et al., 2007b , 2010 ; Fox et al., 2012 ). Aftershocks largely occurred at 14–16 km below the slip range, accompanied by a swift decline in the number of earthquakes in the cover (Yaminifard et al. 2012 ; Nissen et al., 2010 , 2014 ). The mainshock ruptured the “Competent Group” and triggered basement microseismicity beneath the Hormuz salt layer (Nissen et al., 2010 , 2014 ). Aftershocks were associated with both positive Coulomb stress changes imparted by the mainshock (up to 0.05 MPa) and areas where there had been negative stress changes (Nissen et al., 2011 ; 2014 ). The Fin mainshock-aftershock sequence The Fin earthquake occurred near the town of Fin, N-Qeshm Island, at 07:29 UTC on 25 March 2006, with E-W striking reverse faulting with a moment magnitude in the range of 5.7–5.9 immediately followed by four aftershocks (Mw 5.5, 5.2, 5.0, 4.9) (Nissen et al., 2014 ). The top and bottom of the rupture were well resolved at 5–6 km and 9–10 km respectively, consistent with 8 km depth and the largest aftershock (09:55 UTC) was modeled, yielding a centroid depth of 4 km (Nissen et al., 2014 ). Approximately 400 aftershocks between magnitudes Mw 1.0 and 4.0 were also recorded in the Fin area (Nissen et al., 2011 , 2014 ). Focal depths were concentrated within the basement with a small peak in aftershock numbers at 14–15 km and a larger one at 20–25 km (Roustaei et al., 2010 ; Gholamzadeh et al., 2009 ; Nissen et al., 2011 , 2014 ). The Qeshm and Fin mainshocks, together with the distributional patterns of their aftershock sequences, reveal almost the same centroid depth structure of earthquake faulting to the Bandar Abbas mainshocks in SFB. The Qeshm, Fin and Bandar Abbas mainshocks-aftershock sequences are located within the middle-lower sedimentary cover at depths where their mainshock co-seismic slips are shallower than most of the observed aftershocks (see Nissen et al., 2011 , 2014 for details) (A-B profile in Fig. 8 , E-F and G-H profiles in Fig. 9 ). The main reason for this phenomenon is that Eq. 1 and Eq. 2 broke strong barriers between two weaker faults upon which stresses were not sufficiently raised to induce aftershocks (Nissen et al., 2014 ). For example, as observed in the C-D profile in Fig. 9 and as reported by Nissen et al., ( 2014 ), several weak-soft layers within the thick sedimentary cover may have had a “dampening effect” on the distributional pattern of aftershock activity at the top and the bottom of the mainshock fault plane (Nissen et al., 2014 ). The aftershocks of the Bandar Abbas mainshocks that distributed at a full depth range of ~ 5–20 km from top to bottom, appear to be distinctly concentrated at a depth range of ~ 10–15 km (Figs. 7 – 9 ), while most of the aftershock focal depths at the Qeshm event occurred at a depth range of ~ 13–16 km consistent with the depth of the weak Hormuz salt in the SE-coastal Fars Arc (Jahani et al. 2009 ; Nissen et al., 2014 ). Although the Hormuz salt is unable to host these aftershocks at such depths (~ 10–16 km) due to the increasing temperature of ~ 200-400 o C (e.g. Franssen and Spiers, 1990 ; Marques et al., 2013 ; Nissen et al., 2014 ), the Hormuz salt can flow along the basement-cover interface due to co-seismic strain of the overlying competent cover (Nissen et al., 2014 ), while the lowermost competent cover is considerably strained but without rupturing. Eventually, the flow of the Hormuz salt, activated by the 2005 Qeshm mainshock, triggered a total of eight aftershocks (Mw 5.0–6.0, from June 2006 to July 2009), which have shallow centroid depths of 4–11 km and are located within the cover (Nissen et al., 2010 , 2014 ). Similarly, in the case of the Bandar Abbas mainshocks, shallow depths of triggered aftershocks are located at a depth range of ~ 5–10 km within the cover (Figs. 8 and 9 ). 4.4.2. Co-seismic surface folding As illustrated in Figs. 5 a-e and interpreted in Fig. 6 , the up-dip limit of co-seismic slip of the Bandar Abbas earthquakes occurred at depths of ∼3–7 km, while the down-dip limit of the ruptures occurred at depths of ∼10–16 km. However, there were no surface ruptures associated with the Qeshm and Fin earthquakes, as the up-dip limit of slip occurred at depths of ∼3–5 km and the base of the ruptures was consistent with the depth of the Hormuz salt (∼8–10 km), which are not estimated centroid depths according to Nissen et al., ( 2014 ) and shallower than our depth range of ∼10–16 km. The reason is that Eq. 1 cuts the basement up to 16 km (Fig. 6 ) and that the weak salt layer prevented slip propagation by forming a barrier at the base of the sedimentary cover (Nissen et al., 2011 ). The up- and down-dip limits of these rupture depths suggest that moderate-sized earthquakes ( M w 5–6) may originate in the lower sedimentary cover associated with asymmetric surface folding (Nissen et al., 2011 ). The ENE-trending area uplifted during the Fin earthquakes is oblique to the overlying E-W-trending fold axes, while the Qeshm earthquakes ruptured a SSE-dipping fault, perpendicular to the overlying anticline axis (Nissen et al., 2011 ). In both cases, and as also seen in the Bandar Abbas earthquakes (Fig. 6 ), the causative faulting and the overlying folding above a low-angle thrust structure are closely connected (Eq. 2 in Figs. 5 e and 6 ) due to the fault plane parallel detachment surface (7–10 km) in the cover, as also reported by Nissen et al., ( 2011 ). These results are strong evidence to suggest that surface anticlines in these epicentral areas are resulted from detachment folding, rather than from forced folding above discrete thrusts (Nissen et al., 2011 ). The predominant mechanism resulting in surface fold generation in other regions of open, symmetric folding across the SFB is assumed to be detachment folding but forced folding also occurs in some areas (Nissen et al., 2011 ). Further observations from earthquakes that occurred in 1972 and 1977 are very similar to or the same as the Bandar Abbas earthquakes. The 1972 Ghir earthquake (Mw ∼6.7 and centroid depth of ∼9 km) (Baker et al. 1993 ) and the 1977 Khurgu earthquake (Mw ~ 6.7 and a centroid depth of ∼12 km) (Nowroozi et al. 1977 ; Jackson and Fitch 1981 ), with diffuse small aftershocks at a depth range of 4–22 km (Nowroozi et al. 1977 ), involved both cover and basement and ruptured through the boundary between these two layers (Nissen et al., 2011 ), which is consistent with Eq. 1 and Eq. 2. Both events occurred near strongly asymmetric anticlines at the surface, allowing significant changes in stratigraphic level (Nissen et al., 2011 ). These asymmetric anticlines are different from the usual gentle symmetrical folds evident in most of the SFB (e.g., the source area of the Fin earthquakes in Nissen et al., 2011 ). At the epicentral area of the Fin event, earthquakes are limited to moderate magnitudes ( M w ∼6.0) because of the structurally weaker (incompetent) layers and also decouple surface folding from the reverse faults present in the lower levels of the cover (Nissen et al., 2011 ). Co-seismic surface folding of the Ghir, Khurgu and Fin events is observed in particular locations, such as the frontal MFF (27.5 o N-52.5 o E) and the NE-Fars Arc (27.7 o N-55.5 o E) (Leturmy et al. 2010 ; Nissen et al., 2011 ), where large fold-related earthquakes may be generated, consistent with the significant seismic hazard in the SFB (Leturmy et al. 2010 ; Nissen et al., 2011 ). The Bandar Abbas mainshocks, in a similar fashion to the Qeshm, Fin, Ghir and Khurgu mainshocks, ruptured the middle-lower part of the cover at approximately 10–12 km (Figs. 2 a and 3 a). Based on the estimated centroid depths in the Fin area (Nissen et al., 2014 ), the proposed Hormuz salt layer ranges between ~ 10 km and ~ 12 km depth in the Bandar Abbas area and this is closely coincident with our depth ranges. This indicates that Eq. 2 and Eq. 1 ruptured the top (cover) and bottom (basement) sections of the salt horizon, respectively. Accordingly, the Bandar Abbas aftershock sequence, ranging from ~ 5 to ~ 20 km depths, was concentrated both within the cover (~ 5–10 km) and also the basement (~ 13–20 km, up to ~ 25 km) (Figs. 8 and 9 ). Triggered aftershocks possibly represent breaking up of neighboring strata as the activated salt flows through the depth range of ~ 10–12 km due to co-seismic strain at the base of the cover. This strongly suggests that most of the moderate earthquakes within the SFB occur within the “competent group” of carbonate sediments that make up the middle-lower parts of the cover (Nissen et al., 2011 , 2014 ). Last but not least, the Bandar Abbas earthquakes, with the Qeshm, Fin, Ghir and Khurgu earthquakes, are perhaps the best examples of activated salt flow-induced moderate earthquakes nucleating within a carbonate sequence (Eq. 2) anywhere in the SFB and generating surface expression of earthquake-related detachment folding (7–10 km) parallel-subparallel to the salt décollement layer (~ 10–12 km). 4.5. Decoupled seismic deformation; thick-skinned versus thin-skinned deformation In the SFB, most of the earthquakes occur within the lower sedimentary cover (~ 10–14 km), with smaller events at depths of up to ∼20–30 km with occasional larger events at depths of up to ∼20 km (Nissen et al., 2011 ). Most seismic strain appears to be released at depths of ~ 5–10 km, supported by teleseismic centroid depths, and this is much less likely to occur at depths of ~ 10–20 km, but there is evidence for this in the form of several moderate-sized earthquakes. Seismic moment release at a depth range of ~ 5–20 km, consistent with the Bandar Abbas mainshock-aftershock sequence depth range, suggests aseismic shortening of the Zagros basement (Nissen et al., 2011 ). In order to provide quantitative values of shortening and to understand the mechanisms of deformation accommodation in the SE-Zagros, Molinaro et al., ( 2004 , 2005 a) constructed cross-sections projected on SFB (Regard et al., 2010 ). In the SE-Zagros, the Bandar Abbas-Hadjiabad section (see the cross-sectional BB’ profile shown in Fig. 3 of Regard et al., 2010 ) there are two markedly different N-S shortening values, ~ 10 (4.5% ratio) for the basement and ~ 45 km (22% ratio) for the cover (Regard et al., 2010 ; Molinaro et al., 2005 ). This large discrepancy implies a complete “decoupling” of shortening in the two layers, as reported by Molinaro et al., ( 2005 ). It has been suggested that deformation in the cover was increased by the effect of the ductile Hormuz evaporites, while shortening was reduced in the basement by thrusting (Regard et al., 2010 ; Molinaro et al., 2005 ). The discrepancy also indicates the two main stages in the evolution of the SFB; thin-skinned deformation with a décollement at depth of ~ 8–9 km during the Mio-Pliocene stage and thick-skinned deformation with a basement through major thrust faults from the Pliocene to the recent shortening stage, inferred from focal mechanisms (Nissen et al., 2011 , 2014 ) and the general topography and structural elevation of the Zagros mountains (Molinaro et al., 2005 ; Regard et al., 2010 ). 4.5.1. Basal salt décollement An intersection at oblique angles between the fault planes of Eq. 1 and Eq. 2 (between shallow-seated cover folding and deep-seated basement thrusting in Figs. 5 and 6 ) led to a discussion of thick-/thin-skinned earthquake faulting, recognizable in the Bandar Abbas area (Molinaro et al., 2005 ), where the faults arise through the cover and obliquely cut the folding (e.g., in the Kuh-e-Khush), due to a number of possibly mechanisms including fold rotation, reactivation of pre-existing structures or stress rotation (Regard et al., 2010 ; Molinaro et al., 2005 ). In the Bandar Abbas earthquakes, as discussed above, the co-seismic deformation involved major low-angle thrusting in the basement (3–16 km) with folding in the cover (7–10 km) controlled by the basal Hormuz salt layer (~ 10–12 km) (Fig. 6 ). The folding is constrained by detachment at a depth range of 7–10 km (Eq. 2), without basement deformation. Thus, we consider that decoupled co-seismic deformation for the Bandar Abbas setting with mechanical stratigraphy describes the deformation pattern of basement thrust structures (Eq. 1) well by characterizing related, shallow, fold-thrust structures arising from similar origins (Eq. 2 and in the central Tarim craton, NW-China, by Chen et al., 2022 ). With specific reference to stratigraphically decoupled deformation characterization, as proposed by Chen et al., ( 2022 ), the salt layer that has low strength and Young’s modulus values compensates for co-seismic strain, mainly through lateral thickness changes (Chen et al., 2022 ). Thus, the salt flow thins in the subsiding areas but thickens in the folding areas, while co-seismically activated. This propagation mechanism is detailed in the following text. Subsequent thrusting-folding caused by the Bandar Abbas earthquakes remobilizes the Hormuz salt, causing it to flow from an area of subsidence (~ 0 km-thick beneath syncline due to its downwarping) toward an area of folding (~ 1–2 km-thick in the core of the anticline) (Edgell, 1996 ; Molinaro et al., 2005 ), consistent with a typical style of detachment folding (Fig. 6 ) (e.g., Colman-Sadd, 1978 ; Molinaro et al., 2004 , 2005 ). The detachment folding is due to the presence of significant structural differences between the sedimentary units involved in the folding process (Molinaro et al., 2005 ), consisting of a basal incompetent layer acting as a detachment zone (salt/shale) overlain by a thick competent unit (carbonates) (Molinaro et al., 2005 ). Thus, the Hormuz salt acts as a basal décollement, allowing the deformation to propagate around 50 km to the NE (at least ~ 50 km in Fig. 6 ) (Davis and Engelder, 1985 ; Molinaro et al., 2005 ). Depletion of the salt at the base of the subsidence, effectively welding the basement and cover together, then favors the progressive propagation of thrusting through the forelimb (Molinaro et al., 2005 ). In Fig. 6 , the fault plane of Eq. 2 corresponds to an upper flat (7–10 km) region accommodating shortening that, in the SW, has arisen from the lower levels of the cover. This is crosscut by the fault plane of Eq. 1 (3–16 km) originating from basement thrust. We consider the upper flat (Eq. 2) to be associated with “fault-bend-folds”, as observed by Molinaro et al., ( 2005 ), transferring maximum displacement (80 cm in Fig. 3 a) from a lower flat (10 km) likely in the Hormuz salt layer (~ 10–12 km) to an upper flat (7 km) (Fig. 6 ). This shortening, transmitted into the cover, allowed the deformation front to extend into the upper flat in the NE, causing the cover to form a series of relatively small detachment folds, parallel-subparallel to basal salt décollement at ~ 10 km depth. 4.5.2. Obliquity of salt deformation related to stress transfer The vectored sum of maximum co-seismic slips of the NW-SE striking pure thrusting (30 cm) in the basement (Eq. 1) and the NE-SW striking oblique thrusting (80 cm) in the cover (Eq. 2) (Figs. 2 a, 3 a, 5 a and b) are ~ 85 cm (max) directed to N, indicating a relatively slight rotational motion of the hanging wall block toward the NE (clockwise rotation), in which the detachment folding occurs (Fig. 6 ). Such a deflection of the detachment folds, located on the hanging wall, indicates the passive draping of the cover which has accommodated the vertical uplift along the fault (Leturmy et al., 2010 ). Bilateral rupture source characteristics and the oblique left-lateral thrust focal with a little strike component (Eq. 2) shown in Fig. 3 a may be due to the effect of the strike-slip movement in the salt décollement on the cover (as also proposed by Ricou 1974 ; Hessami et al. 2001 ; Leturmy et al., 2010 ), such as when the salt layer is obliquely oriented to the shortening direction. The weakness of the salt layer easily favors maximum lateral propagation (~ 85 cm) to the N and rotation of detachment folds toward NE, thus localizing deformation in a distinct trend to the NE and generating relatively little left-lateral strike-slip component in the cover, which is required to generate the bending of the small folds (Callot et al., 2007 ; Jahani et al., 2009 ; Leturmy et al., 2010 ). Maximum co-seismic slip (30 cm) along pure thrusting in the basement (Fig. 2 a) is not sufficient to completely overprint the folding that exhibits a deflection oblique to the salt décollement (Fig. 6 ). In the E-arm of the SFB, particularly around the Bandar Abbas area, the majority of folds frequently display such distinct deflections in a trend toward a NE-SW orientation, such as the Shab anticline (Leturmy et al., 2010 ). The Kuh-e-Muran is, perhaps, one of the best structures, being surrounded by salt plugs and associated with an initial NE-SW salt wall that controls the position of the structure (Jahani et al., 2009 ; Leturmy et al., 2010 ). This has been interpreted as activation of a NE-SW basement reverse fault running parallel to the Kuh-e-Muran structure that has elevated the earlier folds on its hanging wall (Leturmy et al., 2010 ). Similarly, an ENE-WSW trending Kuh-e-Khush structure, linked to the HZF and superimposed over the NW-SE trend of an early fold, has also been proposed to be related to a basement fault (Molinaro et al., 2005 ; Leturmy et al., 2010 ). Low-angle thrust faults cutting obliquely through the detachment folds (Eq. 2) with a salt layer controlling the fold geometry, as in the Kuh-e-Muran structure (Jahani et al., 2009 ) is also proposed by Molinaro et al. ( 2005 ) for the Kuh-e-Khush structure and is consistent with the geological and morphological data and focal mechanisms recorded in the area (Leturmy et al., 2010 ). As inferred from cross-sectional depth profiles projected on the fault plane of Eq. 2 (shown in Fig. 9 ) and co-seismic slip pattern of Eq. 2 (shown in Figs. 3 a and 6 ), our interpretation is that the salt most probably propagates through the basement-cover interface at a depth range of ~ 10–12 km toward the NE. We infer that this propagation appears to be prominent in a few profiles, along which co-seismic stress changes are decoupled and co-seismic slips are large. For example, the salt flow seems to propagate along the C-D profile in Fig. 9 with large co-seismic slips (~ 40 to ~ 60 cm in the central part of the rupture along the C-D profile), in which stress changes are decoupled. However, the salt flow is only partly observable in the A-B profile, where stress changes are only partly decoupled and co-seismic slips substantially decrease in a range of ~ 0–20 cm (the up-dip limit of the rupture along the A-B profile). This may be valid for the E-F profile (down-dip limit of the rupture), along which salt flow is partly clear with small co-seismic slips (~ 0–10 cm) and decoupled stress changes. We propose that the presence of the salt flow, parallel/subparallel to the fault plane of Eq. 2 (Fig. 6 ), considerably controls, distributes and/or accelerates the co-seismic slips of Eq. 2, and also Eq. 1 during its relatively rapid propagation toward NE. We suggest that this is, in fact, the main cause of the bilateral rupture sources of both earthquakes (Figs. 2 a and 3 a). In doing this, the salt activates and drives co-seismic stress transfer and redistributes the high-to-low/low-to-high stress changes. Finally, the fold deformation front, propagating toward NE with wavelengths in the region of tens of kilometers (Fig. 6 ), is needed to accommodate deformation of the basement (e.g., Mouthereau et al., 2007 ; Malekzade et al., 2016 ). This implies “synchrony” between thin- and thick-skinned deformations (Hatzfeld et al., 2010 ; Malekzade et al., 2016 ), consistent with seismic and GPS measurements (Masson et al., 2005 ; Malekzade et al., 2016 ). 4.6. Tectonic implications for the rupture decoupling process Low-angle, blind thrust deformations in the Bandar Abbas source area imply that two steps of well-known deformation can be distinguished within the area. In the case of Eq. 2, shortening is accommodated within the cover both by low-angle thrusting and by large-scale folding, consistent with thin-skinned cross-sections of Molinaro et al., ( 2005 ). In the case of Eq. 1, major out-of-sequence basement thrusts with strong seismicity records cut through the overlying structures of the cover (Molinaro et al., 2005 ), consistent with the thick-skinned cross-sections of Molinaro et al., ( 2005 ), which illustrate that a thrust fault linked to a deep basement ramp cuts the fold at an oblique angle (Molinaro et al., 2005 ). This is consistent with previous suggestions that large thrust faults with significant displacement cut through both basement and cover (Blanc et al., 2003 ; Alavi, 2007 ; Vergés et al., 2011; Molinaro et al., 2005 ). The Eq. 1 and Eq. 2 mainshocks in the Bandar Abbas area are, therefore, the clearest examples of the rupture decoupling process exhibiting slip distribution geometry of thick-skinned and thin-skinned co-seismic deformations (Figs. 2 , 3 and 6 ). Both earthquakes support and confirm successive thin-skinned and thick-skinned deformation, such as the Jain, Faraghun, and Kuh-e-Khush structures reported in Molinaro et al. ( 2005 ). Source mechanisms of both earthquakes reveal that the thick-skinned mainshock (Eq. 1) initially ruptured at approximately the depth level of the bottom of the salt (~ 12 km) and rapidly mobilized the Hormuz salt at the same depth, then rapidly triggered and activated the thin-skinned mainshock (Eq. 2). Eq. 2 ruptured at approximately the depth level of the top of the salt (~ 10 km) and generated the co-seismic detachment folds, similar to the very rapid propagation of deformation in similar settings described previously (Letouzey et al., 1995 ; Cotton and Koyi, 2000 ; Costa and Vendeville, 2002 ; Molinaro et al., 2005 ). As observable in the STFs of Figs. 2 a and 3 a, such a rapid propagation of ruptured, mobilized, triggered and activated successive deformations may have resulted from simultaneous activation of the basal décollement salt horizon and the detachment folding over a wide area (Molinaro et al., 2005 ), consistent with GPS data and seismic measurements (Hatzfeld et al., 2010 ; Malekzade et al., 2016 ; Masson et al., 2005 ). We consider that such shorter-term successive deformation activation requires a closer relationship and interaction of previously existing structures, including folds, detachments, and evaporates, over the same wide area (e.g., Molinaro et al., 2005 ). As interpreted from rupture source areas of Eq. 1 and Eq. 2 at the Bandar Abbas location of the SFB, the fold-thrust belt is co-seismically deformed by large basement and cover thrusts with "ramp-flat" geometries as proposed by Vergés et al., (2011), where the thrust ramp in the basement is separated from the deformation front and located ahead in the sedimentary cover above flat segments of the same thrust. The ductile style (continuous and discretely distributed strain) of the salt accommodates most of the deformation in the incompetent shallow cover (Chen et al., 2022 ), causing a lack of surface rupture and/or brittle failure. Thus, ductile shear facilitates the change from oblique thrust faulting in the cover to pure thrust faulting in the basement, vertical axis rotation and, perhaps, strain partitioning, but this concept is beyond the scope of this study. It is essential to note that, in the Bandar Abbas area with a weak deformation pattern, mechanical stratigraphy more effectively demonstrates its control on long wavelength surface folding, low-angle blind thrust faulting and the rupture decoupling process than expected (e.g., Asaoka et al., 2016 ; Chen et al., 2022 ). Finally, the rupture decoupling is typical of fold-thrust belts where the cover-basement contact is extremely weak, such as in the Alps, the Betics and the Pyrenees (Vergés et al., 2011). The thin-skinned earthquake faulting events, as predominant seismic features of the SFB, are affected by larger wavelength processes of thick-skinned earthquake faulting events (Vergés et al., 2011), similar to the past stage of Himalaya, consistent with Hatzfeld and Molnar, ( 2010 ) and Malekzade et al. ( 2016 ). 5. Conclusions Co-seismic slip distribution models consist of relatively fast rupture sources of Eq. 1 and Eq. 2 that occurred on a low-angle, blind, pure thrusting (NW-SE)/oblique left-lateral thrusting (NE-SW) in the basement-cover interface, with centroid depths of 12 − 10 km, along fault lengths of ~ 40–50 km, at depth ranges of 3–16 km and 3–15 km, respectively. Shallow off-fault deformation implies long wavelength-low amplitude co-seismic surface folding in the detached cover (at depths of 7–10 km) with a maximum slip of 80 cm to NE. Coulomb stress changes load and trigger both fault planes in areas where faults are brought closer to failure, and influence along-strike co-seismic strain distribution to NE. The SW-NE trending on/off fault stress triggering through shallow ( 10 km) sections suggests coupled/decoupled interaction of the co-seismic stress variations along both fault planes, which indicate that stress decoupling propagating from the SW to the NE corresponds to the salt décollement (at depths of 10–12 km). The weak salt layer, co-seismically ruptured and rapidly mobilized, compensates for co-seismic strain through lateral thickness changes; the salt flow propagates from the SW through the subsiding area to the folding area to the NE. The pure thrust faulting, with a maximum slip of 30 cm to NE, affecting both basement and cover (at depths of 3–16 km), and occurring in a particular zone beneath the surface folding, obliquely disrupts the detachment in the cover and generates a single detachment level above the salt décollement. This indicates a clear association between causative faulting and overlying detached folding. Rupture decoupling for both events with mechanical stratigraphy can well describe the deformation pattern of basement thrust structure by characterizing the genetically related shallow fold-thrust structure. The Bandar Abbas earthquakes are thus the best examples of the rupture decoupling process that exhibits distinct co-seismic slip pattern geometry of the successive thick-/thin-skinned deformation styles. Thick-skinned Eq. 1 ruptured and mobilized the salt layer, then triggered and activated thin-skinned Eq. 2 that generated the co-seismic detachment folds, which the ductile salt accommodates in the shallow cover. Thus, basal ductile shear facilitates the change from pure thrust faulting in the basement to oblique thrust faulting in the cover. In the Bandar Abbas area, mechanical stratigraphy more distinctly demonstrates the control on long wavelength surface folding, low-angle blind thrust faulting, and the rupture decoupling process. Anomalous interference patterns through superimposed fault planes of the Bandar Abbas earthquakes with a ductile salt horizon indicate that the thin-skinned faulting events are predominantly affected by larger wavelength processes of thick-skinned faulting events in the Bandar Abbas area of SFB. This has implications for the deformation chronology of the thick-/thin-skinned phases of Zagros orogeny. 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Cite Share Download PDF Status: Published Journal Publication published 26 Oct, 2023 Read the published version in Environmental Earth Sciences → Version 1 posted Editorial decision: Major revision 24 Jun, 2023 Reviews received at journal 11 Jun, 2023 Reviewers agreed at journal 15 May, 2023 Reviewers invited by journal 05 Mar, 2023 Editor assigned by journal 31 Jan, 2023 Submission checks completed at journal 31 Jan, 2023 First submitted to journal 30 Jan, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2531086","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":171997576,"identity":"ac58309f-ce80-4893-8c38-a6c350259141","order_by":0,"name":"Mustafa Toker","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuUlEQVRIiWNgGAWjYFACNjApByIOPCBGAw9UizFYSwIpWhIbQCRRWuzZ2xIfV+YcTp8fdvgh0BY7Od0GQrbwHDtseHbb4dyNt9MMgFqSjc0OENIikd4m2QjSMjsBpOVA4jYitLT/BGpJN5yd/oFYLWnHGIFaEuSlc4i15cyxZKDD0g03SOcUHEgwIMIv7O1thh8bt1nLy89O3/zhQ4WdHEEtcGAAVmlArHIQkG8gRfUoGAWjYBSMKAAAB0VFw7xH5ZEAAAAASUVORK5CYII=","orcid":"","institution":"Yuzuncu Yıl University","correspondingAuthor":true,"prefix":"","firstName":"Mustafa","middleName":"","lastName":"Toker","suffix":""},{"id":171997577,"identity":"51db3f04-10da-4d19-8a0f-5b527c7c3455","order_by":1,"name":"Hatice Durmuş","email":"","orcid":"","institution":"Dumlupınar University","correspondingAuthor":false,"prefix":"","firstName":"Hatice","middleName":"","lastName":"Durmuş","suffix":""},{"id":171997578,"identity":"d1e13811-7a9a-4aaf-ada0-ad4108eb90bf","order_by":2,"name":"Murat Utkucu","email":"","orcid":"","institution":"Sakarya University","correspondingAuthor":false,"prefix":"","firstName":"Murat","middleName":"","lastName":"Utkucu","suffix":""}],"badges":[],"createdAt":"2023-01-30 19:29:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2531086/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2531086/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12665-023-11232-3","type":"published","date":"2023-10-26T15:02:32+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":32347722,"identity":"6782942a-2abb-4415-a389-727e40ef4501","added_by":"auto","created_at":"2023-02-01 19:36:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":681100,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003eSimplified tectonic map (taken and modified from Molinaro et al., 2005) showing main structural features of the SE-Zagros Simple Fold Belt (ZSFB) with topographic elevation scale in meter (m) and locations of the 2021 Bandar Abbas earthquakes (red dots). Inset map showing the principal tectonic features of the Arabian-Iranian convergent margin (taken from Molinaro et al., 2005). Boxed area in red indicates location of the Bandar Abbas area and its simplified structural inset map (taken and modified from Molinaro et al., 2005, compiled from geological maps of National Iranian Oil Company NIOC and authors’ fieldwork in Molinaro et al., 2004 and references therein), showing main fold axes (short thin lines) and thrusts (thick line with triangles); smaller thin arrows in black on the map refer to the major anticlines (arrows outward) and synclines (arrows inward), dashed thick lines in black indicate basement faults and light blue shading indicates NNW trending structures of the Zendan Minab Belt (ZMB) (Molinaro et al., 2005), SSZ, Sanandaj Sirjan Zone; UDMA, Urumieh Dokhtar Magmatic Arc; MZT, Main Zagros Thrust; ZF, Zendan Fault; KF, Kazerun Fault; JF, Jiroft Fault; MFF, Mountain Front Fault; HZF, High Zagros Fault; HZB, High Zagros Belt, \u003cstrong\u003e(b)\u003c/strong\u003e Updated seismicity map of Iran compiled from Iran Seismological Center (data source IRSC) showing the earthquakes during a year of 2021 and locations of the 2021 Bandar Abbas earthquakes (red box).\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/cb179b9ba31d9ddf43dc20dc.png"},{"id":32347730,"identity":"8b5fb5b3-4141-49e2-b7b4-21449c95b8e7","added_by":"auto","created_at":"2023-02-01 19:36:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":556699,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea.\u003c/strong\u003e Preferred co-seismic slip distribution model for the November 14, 2021, Bandar Abbas mainshock (Mw 6.0, Eq 1). Slips are contoured at 5-cm intervals. The white star shows the hypocentre location, \u003cstrong\u003eb.\u003c/strong\u003e Comparison of the teleseismic P velocity waveforms with the observed waveforms predicted for the moment tensor (CMT) solution given in \u003cstrong\u003ea.\u003c/strong\u003e \u003cstrong\u003ec.\u003c/strong\u003e Comparison of the teleseismic P velocity waveforms with the observed waveforms (solid curves) predicted (dashed curves) for the slip model given in \u003cstrong\u003ea\u003c/strong\u003e; station names (left) and azimuths (right) given above each observed-synthetic seismogram pair and the numbers to the right of each pair indicate synthetic-to-observed (peak amplitude) ratios.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/685c09658fac780483521aae.png"},{"id":32348702,"identity":"0a518dfa-9169-457b-9040-35709467343f","added_by":"auto","created_at":"2023-02-01 19:52:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":660346,"visible":true,"origin":"","legend":"\u003cp\u003ePreferred co-seismic slip distribution model for the November 14, 2021, Bandar Abbas mainshock (Mw 6.4, Eq 2). Slips are contoured at 10-cm intervals. The red arrow indicates the main propagation direction to NE. The other details are the same as those shown in Fig. 2.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/8bf1130330f5327ab929c4c9.png"},{"id":32347723,"identity":"608325ee-2c66-4fd3-b54c-1c0196435747","added_by":"auto","created_at":"2023-02-01 19:36:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":587612,"visible":true,"origin":"","legend":"\u003cp\u003eVertical displacement fields generated by the 2021 Bandar Abbas earthquakes at 12-10 km depth range using the co-seismic slip models shown in Figs. 2a and 3a. (\u003cstrong\u003ea) \u003c/strong\u003evertical displacement field on the fault plane of Eq 1 and its comparison with corresponding slip model shown by dashed black lines, (\u003cstrong\u003eb) \u003c/strong\u003evertical displacement field on the fault plane of Eq 2 (superimposed fault planes) and its comparison with corresponding slip model shown by dashed black lines. Green lines are the fault planes, red and blue arrows corresponding to the slips are uplifts (+) and downlifts (-), respectively. Note that the uplifts towards NE and the subsidence in the SW are observable in \u003cstrong\u003eb\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/4569eae63e6b6c709bfefc2c.png"},{"id":32348445,"identity":"ebf544c3-35b8-4792-9396-d5fa36430310","added_by":"auto","created_at":"2023-02-01 19:44:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1078743,"visible":true,"origin":"","legend":"\u003cp\u003eHorizontal displacement fields generated by the 2021 Bandar Abbas earthquakes at 12-10 km depth range using the co-seismic slip models shown in Figs. 2a and 3a. The other details are the same as those shown in Fig. 4. (\u003cstrong\u003ea) \u003c/strong\u003eNW-SE trending cross-sectional A-B profile projected on the horizontal displacement field on the fault plane of Eq 1 and its depth cross-section shown in \u003cstrong\u003e(c). \u003c/strong\u003e(\u003cstrong\u003eb) \u003c/strong\u003eNE-SW trending cross-sectional C-D profile, together with A-B profile, projected on the horizontal displacement field on the fault plane of Eq 2 (superimposed fault planes), and their depth cross-sections shown in \u003cstrong\u003e(d) \u003c/strong\u003eand\u003cstrong\u003e (e)\u003c/strong\u003e.\u003cstrong\u003e \u003c/strong\u003eThe SW-NE trending section shown by a red rectangle in \u003cstrong\u003e(e)\u003c/strong\u003e is detailed in Fig. 6.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/73a8da10b4edef5f2d8d619f.png"},{"id":32347729,"identity":"9989d585-9206-4ffc-874e-266c44c94189","added_by":"auto","created_at":"2023-02-01 19:36:33","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":813021,"visible":true,"origin":"","legend":"\u003cp\u003eDetailed interpretation of the NE-SW striking depth cross-section (C-D profile) seen in Fig. 5e by combining maximum horizontal and vertical displacement vectors (black arrows) deduced from the co-seismic slip models shown in Figs. 2a and 3a. Half arrows in red show the fault motions on both fault planes; the direction of the motion on the detachment surface, the fault plane of Eq 2, from 10 km to 7 km and thrust fault motion of Eq 1 between 3-16 km. Thick orange arrows indicate the inferred salt flow propagation direction towards NE (~10-12 km), the thin orange line shows the basal salt décollement layer, at a depth of ~10 km, up to ~12 km, between cover and basement, parallel/subparallel to the detachment surface of Eq 2. White arrows show the opposed directions towards the main fault locations (MFF in SW and HZF in NE) in the SFB (see Fig. 1a). Notice the co-seismic detachment folds generated by the hanging wall deformation of Eq 2 above the detachment and note that the top and bottom rupture limits of Eq 1 and Eq 2 range from 3-16 km to 7-10 km, respectively (see the text for further discussion).\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/961093524de56b8fb682e3f3.png"},{"id":32347726,"identity":"e0b16ed3-f3a2-4cf0-9a3b-a3ad474d0c83","added_by":"auto","created_at":"2023-02-01 19:36:33","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":913933,"visible":true,"origin":"","legend":"\u003cp\u003eCo-seismic stress changes of the 2021 Bandar Abbas mainshocks and their located 308 aftershocks (\u003cem\u003eM ≥ 2.5\u003c/em\u003e, labelled as open circles) recorded during the subsequent two months and calculated over the specified rupture planes along the optimally oriented strike-slip faults at a depth of 10 km. \u003cstrong\u003e(a)\u003c/strong\u003e Coulomb failure stress changes calculated over the rupture plane of Eq 1 and (\u003cstrong\u003eb)\u003c/strong\u003e over the rupture plane of Eq 2 (superimposed fault planes). Note that the SW-NE trending stress triggering zone through the superimposed, loaded fault planes of increased stress in \u003cstrong\u003eb\u003c/strong\u003e is closely consistent with the hanging wall deformation of Eq 2 above the detachment shown in Fig. 6 (see the text for further discussion).\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/5e09e64981ade9b4d2fe09c9.png"},{"id":32347727,"identity":"69f0bc2e-9b5f-4110-9031-9ca239c251fc","added_by":"auto","created_at":"2023-02-01 19:36:33","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":636196,"visible":true,"origin":"","legend":"\u003cp\u003eNW-SE and NE-SW trending cross-sectional depth A-B and C-D profiles of Coulomb failure stress changes calculated over the rupture plane of Eq 1, as shown in Fig. 7a. Note that the NW-SE trending (A-B profile) “on-/off-fault stress triggering” lobes through the loaded fault plane of increased stress are consistent with a cluster of diffused aftershocks and activated off-fault hanging wall deformation of Eq 2 above the detachment shown in Fig. 6 (see the text for further discussion).\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/2e99b4bbc2fb2e1317cbfad4.png"},{"id":32348447,"identity":"ae20e8aa-d0a9-49f2-a03f-12d342c20a4c","added_by":"auto","created_at":"2023-02-01 19:44:33","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":548401,"visible":true,"origin":"","legend":"\u003cp\u003eSW-NE trending A-B, C-D, E-F and NW-SE trending G-H cross-sectional depth profiles of Coulomb failure stress changes calculated over the rupture plane of Eq 2, as shown in Fig. 7b. A-B and E-F cross-sections projected on the top and bottom limits of the rupture, respectively, suggest only partial stress decoupling. The C-D cross-section projected on the central, maximum slip, part of the rupture shows full stress decoupling through the detachment surface along the salt décollement layer, consistent with both activated (stress triggering to SW; subsiding at ~10 km depth) and also deactivated (stress shadowing to NE; folding at ~7 km depth) off-fault hanging wall deformation of Eq 2 above the detachment shown in Fig. 6. The decoupling is distinct in places, through which the salt flow propagates (thick orange arrows) towards the NE from the SW (see the text for further discussion).\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/28e5a885bcea5934a36a508a.png"},{"id":45454184,"identity":"f45ef7bf-9607-4e51-968f-5ae20ac7fc14","added_by":"auto","created_at":"2023-10-30 15:09:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5886158,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2531086/v1/639bd3b0-3cf0-4145-a0f9-8527c02fd0f4.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eDecoupled co-seismic deformation and stress changes during the 2021 (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eMw 6.0, 6.4\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e) Bandar Abbas earthquakes, SE-Syntaxis of Zagros, Iran; New insights into the rupture decoupling process\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe Zagros Mountains of SW-Iran, ~\u0026thinsp;1500 km in length and ~\u0026thinsp;300 km wide, are seismically highly active with the most rapidly deforming fold-and-thrust structure, and are thus the most critical tectonic element of the Alpine-Himalayan belt (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Vernant et al. \u003cspan citationid=\"CR108\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The range has proven to be a famous testing base for various seismic mechanistic models of fold-and-thrust deformation (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) and centroid depths of high-quality earthquake mechanisms recorded in the range (at least\u0026thinsp;~\u0026thinsp;200 focals and ~\u0026thinsp;100 centroid depths in Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDistinct sequential succession of the range stratigraphy has had a significant effect on the resulting deformation patterns, with a sedimentary cover of ~\u0026thinsp;10\u0026ndash;15 km thick (e.g. O\u0026rsquo;Brien 1957; James and Wynd \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1965\u003c/span\u003e; St\u0026ouml;cklin \u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e1968\u003c/span\u003e; Falcon \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1969\u003c/span\u003e; Colman-Sadd \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) that is a combination of mechanically resilient carbonates and less resilient evaporates (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). However, most of the stratigraphic and faulting studies obtained only from field geology (e.g., Molinaro et al, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) are neither supported nor validated by various types of seismological studies and have been the topic of previous significant studies being discussed for many years (e.g. Jackson and Fitch \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1981\u003c/span\u003e; Berberian \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Talebian and Jackson \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRecognizing different types of earthquake occurrences through the stratigraphic column into the basement (or \u003cem\u003evice versa\u003c/em\u003e) is particularly challenging in seismically highly active, folded-thrusted belts with detailed analyses of fault source parameters inverted from teleseismic and regional earthquake data in order to discriminate the faulting at different depths (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The Simply Folded Belt (SFB), the outer part of the range (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), offers an excellent example, comprising a substantial covering sedimentary layer (~\u0026thinsp;10 km) together with cryptic reverse faults within which significant and damaging earthquakes have occurred (e.g., Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Talebian and Jackson, \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrevious research reported that the SFB earthquakes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) involve basement faulting due to the absence of co-seismic ruptures (Walker et al. \u003cspan citationid=\"CR110\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). However, new geodetic research has suggested that co-seismic faulting may be present in the sediments, at cover depths of ~\u0026thinsp;4 and ~\u0026thinsp;9 km (up to \u003cem\u003eM\u003c/em\u003ew\u0026thinsp;~\u0026thinsp;6.0, Nissen et al. 2007, \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Roustaei et al. \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). As revealed by Nissen et al., (\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), well-constrained and locally recorded mainshock-aftershock sequences of observed earthquakes occur in the basement at depths of ~\u0026thinsp;10\u0026ndash;20 km. Therefore, these events and the mainshock faulting in the covering layer are distinct (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). For example, the SFB earthquakes (between 51.5\u003csup\u003eo\u003c/sup\u003e and 56.7\u003csup\u003eo\u003c/sup\u003eE and up to 29.5\u003csup\u003eo\u003c/sup\u003eN) at Qeshm Island in 2005\u0026ndash;2008, Fin in 2006, and Khaki-Shonbe in 2013, were shown to have occurred in covering layers (\u0026sim;5\u0026ndash;9 km) but the associated aftershocks where demonstrated to have occurred in basement layers (Barnhart et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Elliott et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Lohman and Barnhart, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Roustaei et al., \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Microseismic events recorded at Qeshm Island (Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), Fin (Roustaei et al., \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), Ghir, Khurgu (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), and Khaki-Shonbe (Elliott et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) indicated a depth range of ~\u0026thinsp;5\u0026ndash;20 km (Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Only some of these events were probably located at basement depths (~\u0026thinsp;10\u0026ndash;20 km) (e.g., Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Tatar et al., \u003cspan citationid=\"CR105\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These previous studies conclude that many of the larger (\u003cem\u003eM\u003c/em\u003ew\u0026thinsp;\u0026gt;\u0026thinsp;5) SFB earthquakes occurred in the so-called \u0026ldquo;Competent Group\u0026rdquo; of mechanically strong carbonates in the middle-to-lower sedimentary layers at depths of \u0026sim;5\u0026ndash;10 km (Barnhart et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Elliott et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Lohman and Barnhart, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Roustaei et al., \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe largest recorded earthquakes in the Bandar Abbas area of the SFB, SE-Syntaxis of the Zagros have not exceeded Mw 6.7 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Nissen et al have suggested that this is due to the Hormuz salt layer made up of weak evaporitic and/or shale horizons, which divides the seismogenic layer of the cover vertically (Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), preventing propagation of seismic rupturing (Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The reverse and thrust faults originate in two regions; the Hormuz salt d\u0026eacute;collement at the base of the cover (Najafi et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) or a secondary detachment occurring in the evaporites in the middle cover (Motamedi et al., \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Furthermore, the salt layer also exerts control over the folds, mainly by d\u0026eacute;collement at depths of ~\u0026thinsp;8\u0026ndash;12 km (Allen et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Motamedi et al., \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Najafi et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, it has been shown that there is significant thrusting in the basement (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Talebian and Jackson, \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). This mechanical separation is evident due to typically narrow co-seismic slip planes of finite-fault source inversion models (Elliott et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Roustaei et al., \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Previous studies suggested that the folding mechanism may have changed over time. The earlier folding was of the detachment type whereas later this manifested as thicker-skinned basement faulting and/or forced folding (Molinaro et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Sherkati et al. \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This is in agreement with an estimated cover shortening of 50\u0026ndash;80 km (Blanc et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; McQuarrie \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Sherkati et al. \u003cspan citationid=\"CR98\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Mouthereau et al. \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This means that no plate-scale reorganization has been suggested which can explain the relation and/or discrepancy between thin- and thick-skinned deformations (e.g., Edey et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) observed in the SFB (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Bandar Abbas Syntaxis of the SFB (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), where the seismicity is largely as a result of blind thrust faulting (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), is a tectonically useful example for comparison with the two peculiar deformation styles in the cover and basement (Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Given the two phases of tectonic evolution in the Bandar Abbas region of the SFB (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) and that there has never been co-seismic surface rupturing in the Bandar Abbas Syntaxis (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), the complex mechanical relationships between buried faulting and surface folding remain controversial, as does the issue of earthquake focal depth, which may occur in the cover and/or the basement. It is therefore crucial to determine the rupture geometry, faulting pattern and surface folding induced by recent Bandar Abbas earthquakes, to complement the previous studies and to understand the relation between the expected thin- and thick-skinned deformations, which may help to resolve many unanswered seismological questions concerning events in the Bandar Abbas region of the SFB. These questions include: \u003cb\u003e(1)\u003c/b\u003e if the basement versus the cover deformation can be decoupled in some way (Allen et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Lacombe et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Nilfouroushan et al., \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Edey et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); \u003cb\u003e(2)\u003c/b\u003e if the Hormuz salt layer contributes to the style and distributional pattern of deformations (Authemayou et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Koyi et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Talbot and Alavi, \u003cspan citationid=\"CR102\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Edey et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) because of the thick salt layers allowing distribution of deformation and accommodation over a wide area (Koyi et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Regard et al., \u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e2004\u003c/span\u003e); \u003cb\u003e(3)\u003c/b\u003e what is the role of Coulomb failure stress changes in triggering and activating the thin-/thick‐skinned ruptures (e.g., Leturmy et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Edey et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); and \u003cb\u003e(4)\u003c/b\u003e whether the Bandar Abbas Syntaxis has been influenced by these two distinct deformations following ruptures of the basement and cover (e.g., fault interference patterns) through the salt layer.\u003c/p\u003e \u003cp\u003eThe two prominent earthquakes which were investigated in this research started with an initial, Mw 6.0 pure thrust faulting event (at 12:07 UTC, 27.71\u003csup\u003eo\u003c/sup\u003e-56.07\u003csup\u003eo\u003c/sup\u003e) and, after a minute, Mw 6.4 oblique left-lateral thrust faulting event (at 12:08 UTC, 27.73\u003csup\u003eo\u003c/sup\u003e-56.07\u003csup\u003eo\u003c/sup\u003e), in the same location at the N-part of the Bandar Abbas Syntaxis on 14 November 2021 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Source parameters of these teleseismically recorded earthquakes and their co-seismic slip distributions using data from the Incorporated Research Institutions for Seismology (IRIS) Data Management Center propose distinct low-angle thrust earthquakes in the Bandar Abbas area (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), allowing this research to re-investigate the relationship between earthquake faulting geometry, the depths at which this occurred and the resulting effects or associations with the surface. Deformation styles deduced from teleseismic waveform inversion and slip modelling of both mainshock ruptures and their focal depths provide evidence of a possible change in the deformation phases in the Bandar Abbas Syntaxis. This change, shown by finite-fault source models and centroid moment tensor (CMT) analyses, marks the transition between two successive phases. These are initial pure thrust motion and subsequent triggered and activated oblique left-lateral thrust motion, which is consistent with clockwise rotation, and NE trending horizontal σ1 axes. Accurately quantifying and representing the focal depths and our preferred model co-seismic slip orientations of both earthquakes may help to resolve the questions concerning the mechanical, structural and seismogenic mechanisms occurring in the Zagros orogeny.\u003c/p\u003e"},{"header":"2. Tectonic Context","content":"\u003cp\u003eThe Zagros Mountain range (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) is one of the world's most active continental seismic belts, study of which has resulted in much greater understanding of the mechanisms of fold-and-thrust earthquake, salt tectonics (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and related halokinesis. The Zagros range marks the leading edge of the collision between the Arabian and Eurasian continental plates (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), which may have begun in the late Eocene or early Oligocene (Allen and Armstrong, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Mouthereau et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; McQuarrie and van Hinsbergen, \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Current GPS measurements show that N-S shortening along the range vary from ~\u0026thinsp;9 mm yr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the SE to ~\u0026thinsp;4 mm yr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the NW (Vernant et al. \u003cspan citationid=\"CR108\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Walpersdorf et al. \u003cspan citationid=\"CR111\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, only a small fraction of the convergence is directly attributable to earthquake moments (Jackson and McKenzie \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Masson et al. \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe 100\u0026ndash;200 km wide SFB, which comprises the SSE-part of the Zagros (Hessami et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Walpersdorf et al., \u003cspan citationid=\"CR111\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), rises from sea level at the SW end to around 1500 metres in height in the NE (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) and exposes the Hormuz salt plugs (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The SFB is separated from the High Zagros (HZ) by the High Zagros Fault (HZF), a major NE-dipping thrust (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The SFB is further subdivided into two lobate salients; high relief Lurestan Arc and Fars Arc, which are separated by a recess with relatively low-lying topography of the Dezful Embayment (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The HZ includes Mesozoic and Palaeozoic sediments with ophiolites (Stoneley \u003cspan citationid=\"CR101\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) and the NW-striking thrust/reverse faults are exposed at the surface; the MZT (Main Zagros Thrust) and the HZF (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The MZT marks the meeting of Arabian and central Iranian structures (Alavi \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) and is coincident with the right-lateral Main Recent Fault (MRF) (Walpersdorf et al. \u003cspan citationid=\"CR111\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The HZF was the location of the only known example of reverse faulting co-seismic surface rupture within the boundary with the SFB, on the 6 November 1990 during the Furg earthquake (\u003cem\u003eM\u003c/em\u003ew 6.5) in the far SE of the SFB (Walker et al. \u003cspan citationid=\"CR110\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) where the HZF is blind and includes gentle folding, typical of the SFB (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMajor changes in both the stratigraphy and elevation across some folds of the SFB are due to major N-dipping basement faults, termed \u0026ldquo;master blind thrusts\u0026rdquo; (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (Berberian, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), one of which is the Mountain Front Fault (MFF). The MFF accommodates\u0026thinsp;~\u0026thinsp;75% shortening (Walpersdorf et al., \u003cspan citationid=\"CR111\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) has a throw of ~\u0026thinsp;2\u0026ndash;4 km, and up to ~\u0026thinsp;6 km in the SFB (Blanc et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Molinaro et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Emami et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Berberian \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Sherkati et al. \u003cspan citationid=\"CR98\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Many earthquakes that have happened in the SFB have originated on the MFF (Jackson and McKenzie, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Ni and Barazangi, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Berberian, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Mouthereau et al., \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) and have a NE-dipping attitude (Tatar et al., 2003; Hatzfeld and Molnar, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The HZF and MFF, with vertical displacement of up to ~\u0026thinsp;6 km (Berberian \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), are highly active beneath the sedimentary cover (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), have been described as major segmented reverse faults, and have seismogenic and morphologic characteristics evident within the SFB (Berberian, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The HZF contributes locally to strain via oblique convergence (e.g. Lettis and Hanson, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; Malekzade et al., 2007), while the MFF exerts a major influence on the flexural basin following collision (Hessami et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2001\u003c/span\u003eb; Sepehr and Cosgrove, \u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Bandar Abbas Syntaxis (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) includes the far E-folds and thrusts of the Fars Arc (Molinaro et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2004\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) and may be considered to consist of two subdomains, the southerly SFB and the northerly HZB (High Zagros Belt), separated by the HZF (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Mechanical stratigraphy of the SFB in the Bandar Abbas Syntaxis\u003c/h2\u003e \u003cp\u003eThe topographic slope across the SFB (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) varies from \u0026lt;\u0026thinsp;1\u003csup\u003eo\u003c/sup\u003e up to 2\u003csup\u003eo\u003c/sup\u003e across the ~\u0026thinsp;100 km-wide strip separating the Dezful Embayment from the HZF (McQuarrie \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2004\u003c/span\u003e), corresponding to a stepped surface, rather than a simple, planar one (Mouthereau et al. \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe SFB contains thick, folded Phanerozoic sediments, which are detached from underlying basement rocks by the Precambrian Hormuz Formation varying in dimension from 1\u0026ndash;4 km (Jahani et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The Hormuz Formation consists of multiple evaporitic and non-evaporitic sediments, evident at the surface as numerous active salt diapirs (Gansser, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1960\u003c/span\u003e; Kent, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1970\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Ala, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1974\u003c/span\u003e; Edgell, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Jahani et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Barnhart and Lohman, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The Hormuz salt is thus brought to the surface in scattered diapirs (e.g. O\u0026rsquo;Brien 1957; Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Furthermore, more robust sediments, dismantled by salt diapirism and folding, within large and intact rafts of between 2\u0026ndash;4 km diameters may be transported to the surface by salt flow (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Lower Mobile Group, comprising late Hormuz evaporites, rests directly on the basement (see Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e for the term \u0026ldquo;basement\u0026rdquo;) and is the main regional d\u0026eacute;collement level for most of the larger folds within the SFB (Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), including detachment and faulted detachment folds, imbrications and duplex structures (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The lower-middle cover, labelled the \u0026ldquo;Competent Group\u0026rdquo; by O'Brien in 1957, is a structurally competent layer (Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The Competent Group comprises a 4000\u0026ndash;5000 metre thick sequence and is the main unit underlying the large wavelength anticlines in the SFB, corresponding to an important regional d\u0026eacute;collement horizon (Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Upper Mobile Group forms the major roof d\u0026eacute;collement and largely decouples deformation below and above underlying structures (Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Faults propagating upward tend to dissipate displacement within the Upper Mobile Group (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). A 2000\u0026ndash;4000 metre thick sequence forms this \u0026ldquo;Incompetent Group\u0026rdquo; (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). This Incompetent Group includes syntectonic sedimentation in the higher regions of the sequence (Hessami et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2001\u003c/span\u003eb) and small-scale thrusting and thrust-related folds extending into the sediments (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). These groups thus comprise a total of ~\u0026thinsp;10\u0026ndash;15 km-Phanerozoic stratigraphic thickness (James and Wynd, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1965\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Sherkati et al., \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Carruba et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Casciello et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Verges et al., \u003cspan citationid=\"CR107\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; O'Brien, \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e1957\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe depth to basement across the SFB has been shown to be within the range 9\u0026ndash;13 km, using cross-sections that include both structural thickening and erosion (Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This range estimate is further suggested by local microseismicity surveys that have shown an increase in body-wave velocities below 10\u0026ndash;12 km (Hatzfeld et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Tatar et al., \u003cspan citationid=\"CR105\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Roustaei et al., \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Yaminifard et al., \u003cspan citationid=\"CR113\" class=\"CitationRef\"\u003e2012\u003c/span\u003ea, b). Others consider the basement depth to be ~\u0026thinsp;8\u0026ndash;12 km (e.g., Allen et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Najafi et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Jamalreyhani et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Based on long-wavelength signals, aeromagnetic data (Kugler \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Morris \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e1977\u003c/span\u003e) has suggested basement depths of 4\u0026ndash;18 km (Talebian \u003cspan citationid=\"CR103\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Other studies have estimated the total sedimentary thicknesses of the SFB to be ~\u0026thinsp;14 km in the NW, ~\u0026thinsp;12 km in the central Fars Arc and ~\u0026thinsp;10 km in the far SE (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (e.g. Colman-Sadd \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; Molinaro et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Sherkati et al. \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Casciello et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The Phanerozoic cover thickness is estimated at 14 (\u0026plusmn;\u0026thinsp;2) km, consistent with mean P-wave velocities of 4.7\u0026ndash;5.7 km/s (Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Seismic structure of the Bandar Abbas Syntaxis\u003c/h2\u003e \u003cp\u003eIn the SFB, seismicity is dominated by blind thrust faulting (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), rarely associated with surface rupturing (Walker et al. \u003cspan citationid=\"CR110\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) so that surface shortening is facilitated by a series of anticlines and synclines (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe mechanism of folding within the SFB depends on either buried faulting or lateral variations in the stratigraphy, or both (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The short-wavelength topography and surface structure of the SFB were originally thought to be detachment folds, formed by buckling of the cover along d\u0026eacute;collements within the sedimentary cover (e.g. Falcon \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1969\u003c/span\u003e; Colman-Sadd \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; Jackson \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e1980\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). A possible cause of this was the shallower d\u0026eacute;collements within the middle sedimentary cover also resulting in surface folding (e.g. Sherkati et al., \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Carruba et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Sepehr et al., \u003cspan citationid=\"CR97\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Verg\u0026eacute;s et al., 2011; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, this would need multiple d\u0026eacute;collements to yield the observed spacing of folds and also the preponderance of folding compared to faulting (Yamato et al., \u003cspan citationid=\"CR112\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Detachment originating in the Hormuz salt has been suggested to allow fault propagation folding over the steep reverse faults which then branch upwards into the cover (McQuarrie, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). An additional complicating factor is the Hormuz diapirism. This affects the location of folding and faulting, particularly in the Bandar Abbas area where salt plugs are most prevalent (Jahani et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). It has been suggested that the sedimentary cover is completely aseismic and faulting only occurs in the basement (e.g. Mouthereau et al. \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The N-dipping blind thrusts form a focus either in the lower reaches of the sedimentary cover (McQuarrie \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Alavi \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) or in the underlying basement, but may penetrate the Hormuz salt to pass into the sediments (Berberian \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe seismicity of the Bandar Abbas Syntaxis, the strongest in the SFB (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), is concentrated at depths of 8\u0026ndash;12 km (Jackson and Fitch, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1981\u003c/span\u003e; Berberian, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Talebian and Jackson, \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) yielding the lowest estimate of depth to basement of ~\u0026thinsp;8 km (Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Between depths of 8 and 17 km, reverse focal mechanisms occur (Talebian and Jackson, \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) which define clear alignments, possibly associated with the MFF and HZF basement faults (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) (Berberian, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). It has been proposed that the ruptures in the basement correspond with the MFF and the HZF (Berberian, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) with focal depths of 10\u0026ndash;11 km for the MFF and 7\u0026ndash;8 km for the HZF (Talebian and Jackson, \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the SFB earthquakes appear to concentrate in the basement zones, as there is no evidence of co-seismic, primary surface rupturing (Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The presence of major basement faults and abrupt changes in stratigraphic level across certain anticlines of the order of magnitude of kilometers (Berberian, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1995\u003c/span\u003e), and data from local microseismic surveys all point to events occurring at basement depths (Hatzfeld et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Tatar et al., \u003cspan citationid=\"CR105\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Roustaei et al., \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Yaminifard et al., \u003cspan citationid=\"CR113\" class=\"CitationRef\"\u003e2012\u003c/span\u003ea, b). Basement faults appear to have developed relatively late in the Pliocene, following the earlier thin-skinned phase of deformation (Molinaro et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Sherkati et al., \u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, there is considerable evidence that centroid depths of large earthquakes appear to predominantly (~\u0026thinsp;75%) occur in at depths of 4\u0026ndash;10 km, suggesting ruptures occurring within the \u0026ldquo;Competent Group\u0026rdquo; of sediments (Jackson and Fitch, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1981\u003c/span\u003e; Kadinsky-Cade and Barazangi, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Jackson and McKenzie, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e1984\u003c/span\u003e; Ni and Barazangi, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Baker et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Priestley et al., \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Maggi et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Talebian and Jackson, \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Adams et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Nissen et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, Nissen et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Data And Methods","content":"\u003cp\u003eIn this study, we used teleseismically recorded broadband P-velocity waveforms, accessed through the IRIS Data Management Centre, to perform finite fault source inversion and to constrain co-seismic slip distributions of the 2021 Bandar Abbas earthquakes using 27 stations with epicentral distances between 32\u0026deg; and 87\u0026deg;.\u003c/p\u003e \u003cp\u003eTime alignment is critical for finite-fault inversion modeling, which uses more P than SH waveforms. This is because P-wave onsets are generally much easier to identify with confidence compared to those of SH waves (Ammon et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The P waveforms data band-pass filtered with corner frequencies (0.01 to 0.5 Hz) were resampled with a time interval of 0.50 s after being corrected for instrumental responses. The first 40 s of the waveform was modeled. In order to avoid deep-seated velocity distortion and/or boundary layer diffraction in the waveforms, the epicentral distances selected for our analysis were chosen in the range from ~\u0026thinsp;30\u0026deg; to ~\u0026thinsp;90\u0026deg;. Parameters selected are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The one-dimensional (1-D) initial crustal velocity model, as compiled from Nissen et al., (\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) and Manaman and Shomali, (\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), used in the inversion is provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParameters of teleseismic data processed for the 2021 Bandar Abbas earthquakes.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEarthquake 1 (Eq.\u0026nbsp;1)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEarthquake 2 (Eq.\u0026nbsp;2)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNumber of stations\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWaveforms\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP velocity waveforms\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eP velocity waveforms\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTeleseismic distance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32\u0026deg; and 85\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u0026deg; and 87\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSampling interval\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.50 s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.50 s\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFilter and corner frequencies\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBand-pass filter (0.01 to 0.5 Hz)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBand-pass filter (0.01 to 0.5 Hz)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThe first 40 s of the waveform\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eThe first 40 s of the waveform\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e1-D initial crustal velocity model structure (compiled from Nissen et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, and Manaman and Shomali, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) used for the inversion in this study (also see Utkucu et al., \u003cspan citationid=\"CR106\" class=\"CitationRef\"\u003e2018\u003c/span\u003e for the model).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThick. (km)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003eP\u003c/sub\u003e (km/s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003eS\u003c/sub\u003e (km/s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eρ (gr/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e33.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.80\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Finite-fault source inversion\u003c/h2\u003e \u003cp\u003eFollowing the same methodology and inversion procedure detailed in the co-seismic slip studies of Utkucu et al., (\u003cspan citationid=\"CR106\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and Durmuş and Utkucu, (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), we performed a finite-fault source inversion method, first described by Hartzell and Heaton, (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1983\u003c/span\u003e), to constrain the co-seismic slip distributions across the fault plane models of the first and second mainshocks (Eq.\u0026nbsp;1 and Eq.\u0026nbsp;2) regarding the previous fault source models (Utkucu et al., \u003cspan citationid=\"CR106\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Durmuş and Utkucu, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe fault planes, divided into subfaults, together with focal depths and source parameters, were modelled in the source areas of both mainshocks. We estimated the point source responses using the generalized ray theory of Langston and Helmberger, (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e1975\u003c/span\u003e). Using a point source, although an approximation, has been demonstrated to be reliable for shallow slip associated with low-angle thrusts (Ammon et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The inversion, based on point-source strength, converts to slip, as each point source is assumed to represent a sub-event with size equal to the distance between sources. In order to simulate radial propagation of the high velocity ruptures, point sources are equally spaced across the fault planes. In order to image sub-fault synthetic seismograms (Green\u0026rsquo;s functions) for each station used, the point source responses are summed with appropriate lagging time corresponding the rupture delay. Then, we convolved the synthetic seismograms with an attenuation operator (\u003cem\u003et*\u003c/em\u003e) as a function of frequency, in this case 0.7 s for \u003cem\u003eP\u003c/em\u003e-wave attenuation (Choy and Cormier, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1986\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDuring inversion, our time window approach allowed estimation of variable slip rise time of each window, represented by isosceles triangles, and the rupture velocity over the model faults, by performing these calculations with an efficient linear inversion based algorithm (due to heterogeneous rupture propagation by Hartzell and Heaton \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Mendoza \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Wald and Thomas \u003cspan citationid=\"CR109\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Ammon et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The method allows each sub-fault to rupture for a specified time interval with a source time function (STF) shape (Ammon et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Thus, we modelled varying velocities of the rupture within an assigned range across the fault plane, depending on the earliest possible rupture time of each point source (high initial velocity of the rupture). The equation expressed by the observed and synthetic waveforms is written as \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eAx\u0026thinsp;=\u0026thinsp;b\u003c/span\u003e, where \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eA\u003c/span\u003e and \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eb\u003c/span\u003e are matrixes defined by synthetic and observed waveforms, respectively and \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003ex\u003c/span\u003e is a matrix defined by slip weights for each subfault. The values of \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003ex\u003c/span\u003e are estimated using a Householder least squares inversion technique (Lawson and Hanson, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e1974\u003c/span\u003e) requiring that \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003ex\u003c/span\u003e and/or solution vector elements are \u0026ge;\u0026thinsp;0. Lastly, in order to image a spatially smooth slip model with minimum seismic moment (Hartzell and Heaton, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Wald and Thomas, \u003cspan citationid=\"CR109\" class=\"CitationRef\"\u003e1994\u003c/span\u003e), we further constrained the solution vector using spatial smoothing through moment minimization.\u003c/p\u003e \u003cp\u003eWe successively perturbed the rupture models in a search for better-fitting models, tried several initial inversion trials for both the mainshocks to properly constrain fault model dimensions and positions with respect to the focal depths. This finally led to identifying a good fit of the data with fixed-rake parameterization. Before selecting the fault dimensions for our models, we also thoroughly explored fault width and length. The parameters used in the finite-fault source modeling of the first (Eq.\u0026nbsp;1) and the second (Eq.\u0026nbsp;2) mainshocks are given in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Parameters also included for Eq.\u0026nbsp;1, fault source parameters of strike 114\u003csup\u003eo\u003c/sup\u003e, dip 32\u003csup\u003eo\u003c/sup\u003e, rake 91\u003csup\u003eo\u003c/sup\u003e and centroid depth of 12 km, with fault and sub-fault dimensions (40 x 25 km and 5 x 5 km, respectively) with a total of 40 sub-faults. Similarly, for Eq.\u0026nbsp;2 these were fault source parameters of strike 49\u003csup\u003eo\u003c/sup\u003e, dip 24\u003csup\u003eo\u003c/sup\u003e, rake 27\u003csup\u003eo\u003c/sup\u003e and centroid depth of 10 km, with fault and sub-fault dimensions (50 x 30 km and 5 x 5 km, respectively) with a total of 60 sub-faults, considering a rupture velocity (\u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eR\u003c/em\u003e\u003c/sub\u003e) of 3.3 km/s, slip rise-fall time of 0.5\u0026ndash;0.5 s and 5\u0026thinsp;\u0026minus;\u0026thinsp;0 of TW-window lag time.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParameterization used in the finite-fault source inversion modeling for the 2021 Bandar Abbas earthquakes.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEarthquake 1 (Eq.\u0026nbsp;1)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEarthquake 2 (Eq.\u0026nbsp;2)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLat.(\u003csup\u003eo\u003c/sup\u003e) - Long. (\u003csup\u003eo\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27.71\u0026ndash;56.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.73\u0026ndash;56.07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePoint-Source (strike/dip/rake)\u003c/p\u003e \u003cp\u003e(s\u003csub\u003e1\u003c/sub\u003e-s\u003csub\u003e2\u003c/sub\u003e)/(s\u003csub\u003e1\u003c/sub\u003e-s\u003csub\u003e2\u003c/sub\u003e)/(s\u003csub\u003e1\u003c/sub\u003e-s\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e114\u003csup\u003eo\u003c/sup\u003e /32\u003csup\u003eo\u003c/sup\u003e /91\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e49\u003csup\u003eo\u003c/sup\u003e /25\u003csup\u003eo\u003c/sup\u003e, 24\u003csup\u003eo\u003c/sup\u003e /17\u003csup\u003eo\u003c/sup\u003e, 27\u003csup\u003eo\u003c/sup\u003e /168\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePoint-Source\u003c/p\u003e \u003cp\u003e(Mo x 10\u003csup\u003e25\u003c/sup\u003e Dyn.cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.80\u0026ndash;2.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFinite-Source (strike/dip/rake)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e114\u0026deg;/32\u0026deg;/91\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e49\u0026deg;/24\u0026deg;/27\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFinite-Source\u003c/p\u003e \u003cp\u003e(Mo x 10\u003csup\u003e25\u003c/sup\u003e Dyn.cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModel fault dimensions\u003c/p\u003e \u003cp\u003e(km x km)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40 x 25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50 x 30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubfault dimensions\u003c/p\u003e \u003cp\u003e(km x km)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 x 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5 x 5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubfault numbers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRupture velocity (V\u003csub\u003eR\u003c/sub\u003e, km/s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRise-fall time (s)\u003c/p\u003e \u003cp\u003e(isosceles triangle)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5\u0026ndash;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.5\u0026ndash;0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTW-window lag time\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u0026thinsp;\u0026minus;\u0026thinsp;0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u0026thinsp;\u0026minus;\u0026thinsp;0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHypocentral depth (km)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTop-bottom depth of fault (km)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.0\u0026ndash;16.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.0\u0026ndash;15.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eDistributional patterns of co-seismic slip models estimated for the 2021 Bandar Abbas mainshocks are given in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, while their corresponding synthetic-observed waveform comparisons are presented in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. Vertical components of co-seismic slip distributions of both mainshocks are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Their horizontal components with corresponding cross-sectional profiles projected on slip models of both events are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. NE-SW striking cross-sectional profile projected on horizontal displacements of both mainshock slips, combined with vertical displacements, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, is jointly interpreted and displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The slip distribution models indicate bilaterally developed low-angle pure thrust faulting (Eq.\u0026nbsp;1) and oblique left-lateral thrust faulting (Eq.\u0026nbsp;2). Both events are heterogeneously ruptured in centroid depths of 12\u0026thinsp;\u0026minus;\u0026thinsp;10 km with conjugate trends to NW-SE and NE-SW, in maximum fault lengths of ~\u0026thinsp;40\u0026ndash;50 km with maximum fault slips of ~\u0026thinsp;30\u0026ndash;80 cm, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Coulomb failure stress changes\u003c/h2\u003e \u003cp\u003eIn this section, Coulomb failure stress changes due to the Bandar Abbas mainshocks are computed to estimate co-seismic stress variations and interactions (Coulomb 3.3 software, Lin and Stein 2004; Toda et al. 2005) between Eq.\u0026nbsp;1 and Eq.\u0026nbsp;2 using the slip distribution models (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) created in this study.\u003c/p\u003e \u003cp\u003eThe Coulomb failure stress change (Δσ\u003csub\u003ef\u003c/sub\u003e) can be defined as:\u003c/p\u003e \u003cp\u003eΔσ\u003csub\u003ef\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;Δτ\u0026thinsp;+\u0026thinsp;\u0026micro; Δσ\u003csub\u003en\u003c/sub\u003e (1)\u003c/p\u003e \u003cp\u003ewhere changes in the shear and the normal stresses are represented by (Δτ) and (Δσ\u003csub\u003en\u003c/sub\u003e), respectively (Harris \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; King et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). The value of the apparent coefficient of friction (\u0026micro;) includes the effect of varying pore fluid pressure ranging from 0.2 to 0.8. We assumed source fault ruptures as rectangular dislocation surfaces, computed after Okada, (\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e1992\u003c/span\u003e), in an elastic half-space with Young\u0026rsquo;s modulus of 8\u0026times;10\u003csup\u003e5\u003c/sup\u003e bar, Poisson\u0026rsquo;s ratio of 0.25 and friction of 0.4. We computed the co-seismic stress changes over the optimally oriented strike-slip fault planes along with the variable slip models using source parameters (strike, dip, rake, fault dimensions) of both mainshocks, given in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea.\u003c/p\u003e \u003cp\u003eImages of calculated co-seismic stress changes are computed at a depth of 10 km, together with ~\u0026thinsp;300 aftershocks (\u003cem\u003eM\u0026thinsp;\u0026ge;\u0026thinsp;2.5\u003c/em\u003e) observed during the subsequent two months and definition of principal stress axes orientations for the regional stress field, are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The azimuth and plunge pairs for the three principal stress axes (σ1, σ2, σ3) are, as compiled from regional stress (world stress map), (333\u0026deg;, 6\u0026deg;), (218\u0026deg;, 75\u0026deg;), (64\u0026deg;, 13\u0026deg;), respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e represents co-seismic stress changes of both mainshocks calculated over optimally oriented strike-slip faults. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea illustrates the stress changes imparted by Eq.\u0026nbsp;1 over its fault plane, while Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb shows the stress changes imparted by Eq.\u0026nbsp;2 over superimposed fault planes of both Eq.\u0026nbsp;1 and Eq.\u0026nbsp;2. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows cross-sectional NW-SE and NE-SW striking A-B and C-D profiles, respectively, projected on the fault plane of Eq.\u0026nbsp;1. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows cross-sectional NE-SW striking A-B, C-D, and E-F profiles parallel to the fault plane and the NW-SE striking G-H profile projected on the fault plane of Eq.\u0026nbsp;2. Most of the located aftershocks, which are densely consolidated in a depth range of ~\u0026thinsp;5\u0026ndash;20 km, are observable on- and end-fault areas of increased co-seismic stress through cross-sections of Eq.\u0026nbsp;1 and Eq.\u0026nbsp;2.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Interpretation And Discussion","content":"\u003cdiv class=\"Section2\" id=\"Sec9\"\u003e\n \u003ch2\u003e4.1. Co-seismic slip distributions\u003c/h2\u003e\n \u003cp\u003eFinite fault-source inversions of azimuthally distributed teleseismic P waveforms and body wave effective source time functions (STFs) yielded co-seismic slip distributions on low-angle thrust faulting geometries.\u003c/p\u003e\n \u003cp\u003eOur preferred model for the 2021 Bandar Abbas thrust faulting event (Eq.\u0026nbsp;1) has a fault orientation of strike 114\u003csup\u003eo\u003c/sup\u003e and dip 32\u003csup\u003eo\u003c/sup\u003e, with nearly pure thrust motion with a rake of 91\u003csup\u003eo\u003c/sup\u003e. For the oblique, left-lateral thrust faulting event (Eq.\u0026nbsp;2), our rupture model geometry has a strike of 49\u003csup\u003eo\u003c/sup\u003e, a dip of 24\u003csup\u003eo\u003c/sup\u003e, and a rake of 27\u003csup\u003eo\u003c/sup\u003e. The major ruptures cover faulted areas of 40 x 25 km (Eqs. 1) and 50 x 30 km (Eq. 2) (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The co-seismic slip, confined to a depth range of 3\u0026ndash;16 km, suggests mostly a bilateral rupture propagation pattern towards NE (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). Our source parameters obtained from the inversion are fairly consistent with the results of the Geological Survey of the United States (USGS) which estimated for Eq.\u0026nbsp;1, strike 91\u003csup\u003eo\u003c/sup\u003e, dip 27\u003csup\u003eo\u003c/sup\u003e, rake 91\u003csup\u003eo\u003c/sup\u003e (40 x 25 km with 40 sub-faults) and for Eq. 2, strike 41\u003csup\u003eo\u003c/sup\u003e, dip 12\u003csup\u003eo\u003c/sup\u003e, rake 22\u003csup\u003eo\u003c/sup\u003e (50 x 30 km with 60 sub-faults). The distribution pattern of the aftershocks also favors the shallow dipping planes as the fault planes of our models; the SW-dipping plane of Eq. 1 aligns better with the aftershock distribution, together with the rupture on a rotated SE-dipping plane of Eq. 2. Our seismic moment was 1.8 x 10\u003csup\u003e25\u003c/sup\u003e (dyn.cm) for Eq. 1, equivalent to a moment magnitude of Mw 6.13, while the seismic moment was 6.9 x 10\u003csup\u003e25\u003c/sup\u003e (dyn.cm) for Eq. 2, equivalent to a moment magnitude of Mw 6.52. Seismic moments of Eq. 1 and Eq. 2 as point sources were 1.38 x 10\u003csup\u003e25\u003c/sup\u003e (dyn.cm) and 2.15\u0026ndash;3.8 x 10\u003csup\u003e25\u003c/sup\u003e (dyn.cm), respectively. Due to a relatively fast V\u003csub\u003eR\u003c/sub\u003e of 3.3 km/s constrained by body-wave directivity, the main rupture lasted about\u0026thinsp;~\u0026thinsp;5 s for Eq. 1 and ~\u0026thinsp;10 s for Eq. 2, with a spatially and poorly resolved weak radiation pattern lasting for ~\u0026thinsp;15 s (Eq. 2) (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eSeveral asperities observed from the slip distribution models range from 10 to 30 cm for Eqs. 1 and 10 to 80 cm for Eq. 2 on the fault planes (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The slip model obtained for Eq. 1 suggested a relatively heterogeneous slip pattern with two distinct asperities. These were dominance of a large asperity (to SE) with a peak slip of ~\u0026thinsp;30 cm and a small asperity (to NW) with a peak slip of ~\u0026thinsp;10 cm located just updip (~\u0026thinsp;8 km) of the focal depth (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). The slip model obtained for Eq. 2 suggested a more heterogeneous slip pattern with five distinct asperities, which were dominance of a large asperity with a peak slip of ~\u0026thinsp;80 cm located just updip (~\u0026thinsp;8 km) of the focal depth and four small asperities (to NE and to SW) with a peak slip of ~\u0026thinsp;10\u0026ndash;20 cm, two of which were located updip (\u0026thinsp;\u0026lt;\u0026thinsp;~\u0026thinsp;4 km) and the other two located downdip (~\u0026thinsp;10 km) of the focal depth (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea).\u003c/p\u003e\n \u003cp\u003eDistributional patterns of co-seismic slip models indicate that the bilateral rupture sources of both mainshocks occurred on low-angle, blinded, pure thrust/oblique left-lateral thrust structures along fault lengths of 40\u0026ndash;50 km (max) in the depth range of 3\u0026ndash;16 km (max).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec10\"\u003e\n \u003ch2\u003e4.2. Co-seismic off fault deformation\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e illustrates the maximum vertical displacement gradient, marked by the sharp contact between blue to red patterns, which are characterized by peculiar circular shapes on surface projections of the co-seismic slips of Eq. 1 and Eq. 2 (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea).\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea shows a weak downlift (-1 cm) and uplift (1 cm) of Eq. 1, which also corresponds to the area of maximum horizontal displacement (~\u0026thinsp;5\u0026ndash;15 cm) and (~\u0026thinsp;15\u0026ndash;30 cm), respectively (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea). In Eq. 1, off fault deformation at a depth range of 3\u0026ndash;16 km was relatively less evident and locally interrupted to the NE by a gentle horizontal gradient (Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea-e). Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb shows a gentler increase of the downlift (up to -3 cm) in the central part of the subsiding area and a little more uplift (2 cm) of Eq. 2, also corresponding to the area of maximum horizontal displacement (~\u0026thinsp;10\u0026ndash;80 cm) (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb). In Eq. 2, off fault deformation was strongly evident by a long wavelength curvature (~\u0026thinsp;50 km in length) and well-localized, small vertical and sharp horizontal displacements toward the NE (Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb-e). This is best traced through the NE-SW striking cross-sectional profile shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee, which is interpreted in detail and shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eIn Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, shallow, off-fault deformation at a depth range of 7\u0026ndash;10 km is characterized by various components of sharp horizontal and small vertical displacements; along the profile striking from SW to NE, a flexural (down) slip of ~\u0026thinsp;20 cm (max), detachment (strike) slip of ~\u0026thinsp;25 cm (max), fold (up) slip of ~\u0026thinsp;15 cm (max), thrust (up) slip of ~\u0026thinsp;10 cm (max) and fold (up) slip of ~\u0026thinsp;5 cm (max) are observed. In Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, in the SW, the hanging wall block of Eq. 2 shows a typical curvature of long wavelength deformation, characterized by downthrow and/or flexural bending through the d\u0026eacute;collement surface toward the fault and a weak bulge up to 2 cm along its hinge zone. To the NE, the displacement gradient decreased (from ~\u0026thinsp;20\u0026ndash;25 cm to ~\u0026thinsp;5 cm) and a weaker uplift (1 cm) formed, leading to the loss of the curvature further to the NE at a depth range of ~\u0026thinsp;5\u0026ndash;7 km; the long wavelength hanging wall deformation over a length of ~\u0026thinsp;50 km decreased where the fault displacement was lower (and \u003cem\u003evice versa\u003c/em\u003e).\u003c/p\u003e\n \u003cp\u003eShallow, off-fault deformation, characterized by a downthrow movement of the hanging wall following a gradual curvature toward the fault to accommodate on fault low-angle movement (d\u0026eacute;collement), implies long wavelength-low amplitude co-seismic surface folding (2 cm max) and subsidence (-3 cm max) with a maximum horizontal displacement (80 cm) along the length of ~\u0026thinsp;50 km (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec11\"\u003e\n \u003ch2\u003e4.3. Co-seismic stress changes\u003c/h2\u003e\n \u003cp\u003eThe co-seismic stress changes shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea indicate that most of the rupture plane of Eq. 1 was loaded by high stress interaction at a depth of 10 km and most of the aftershocks fell into the stress increase area in SE. The stress changes imparted by Eq. 1 loaded and activated the NE-SW striking fault plane of Eq. 2 and aftershock cluster in SE. Meanwhile, the W-, E- and S-parts of both fault planes were unloaded and deactivated, generating stress shadow zones, where some aftershocks were observable. In Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb, the hypocentres of Eq. 1 and Eq. 2 and most of the aftershocks remain in the areas of stress increase. The aftershocks that covered the SE part mostly showed positive correlation with the stress changes and completely fell into the stress enhanced area, while the aftershocks in the S-part remained in the stress decreased area (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb).\u003c/p\u003e\n \u003cp\u003eAs seen in Figs. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb, the rupture geometry of the fault plane and smaller stress interaction (0.1 bar) imposed by Eq. 1 loaded and triggered the NE-SW striking fault plane of Eq. 2, which in turn unloaded and deactivated (-0.1 bar) W-, E- and S-parts of both fault planes. In both rupture patterns associated with high-low stress periods at a depth of 10 km, the hypocentral sections of Eq. 1 and Eq. 2 remained in a high stress area. An area of increased stress pattern, striking NE-SW subparallel to the fault plane of Eq. 2, implies strong successive \u0026ldquo;along-strike\u0026rdquo; activation of the low-angle thrust faulting to NE and to SW on the co-seismic stress transfer. This is best explained by cross-sectional depth profiles of co-seismic stress interactions between Eq. 1 and Eq. 2, as shown in Figs. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eIn Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e, at sections below and above 10 km depth, there are distinct off fault areas of increased stress, while end fault areas of decreased stress are also observable, indicating that shallow and deep sections of the fault plane of Eq. 1 with on fault events activated \u0026ldquo;off fault triggering\u0026rdquo;, up to 0.1 bar. Figure \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e shows, along the A-B profile, both shallow (\u0026lt;\u0026thinsp;10 km) and deep (\u0026gt;\u0026thinsp;10 km) areas of increased stress propagating toward NE, which suggests stress coupling in the NE with a shallow area of increased stress to the SW. In Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, the C-D profile, projected on hypocentral sections of both fault planes, shows shallow-to-deep and deep-to-shallow areas of high-to-low and low-to-high stress toward NE and SW, which suggests strong decoupling of the co-seismic stress transfer. In Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, the E-F profile shows shallow and deep areas of increased stress propagating toward SW, which suggests stress coupling in SW with shallow-to-deep and deep-to-shallow areas of low-to-high and high-to-low stress toward the NE, suggestive of stress decoupling. The G-H profile shows shallow and deep areas of high-to-low and low-to-high stress propagating toward SE and NW, which again suggests stress coupling (Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eIn each case of the profiles shown in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, the source fault planes of Eq. 1 and Eq. 2 remain highly loaded by an increase of stress that indicates \u0026ldquo;on-fault triggering\u0026rdquo;, consistent with \u0026ldquo;off-fault triggering\u0026rdquo; shown in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. Deeper areas (\u0026gt;\u0026thinsp;10 km) of increased stress show stress triggering and seismic activation (A-B, C-D, E-F profiles), but shallower areas (\u0026lt;\u0026thinsp;10 km) of decreased stress show stress shadowing and seismic deactivation (C-D, E-F profiles) toward NE. This implies the SW-NE striking on-fault/off-fault stress triggering through both shallow and deeper areas, suggesting coupled and decoupled interaction of the co-seismic stress variations through both source fault planes of Eq. 1 and Eq. 2. We propose that the coupling-decoupling complexity of co-seismic stress cycles along both fault planes is caused by superimposed and buried low-angle rupture sources (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). The co-seismic slip led to a decrease of the normal stress and an increase of the shear stress on the fault plane, with a low dip angle that makes low frictional strength slip (e.g., Duan et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). The low-angle rupture sources appear to be consistent with segmental fault geometries (e.g., flat-ramp-flat geometry) with fault surfaces inclined at varying angles of 4\u003csup\u003eo\u003c/sup\u003e-35\u003csup\u003eo\u003c/sup\u003e (Chen et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e; Duan et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec12\"\u003e\n \u003ch2\u003e4.4. Centroid depth structure of earthquake faulting phenomena in SFB\u003c/h2\u003e\n \u003cp\u003eWe have presented the following:\u003c/p\u003e\n \u003cp\u003e(a) the co-seismic slip distribution models consist of relatively fast rupture sources of Eq 1 and Eq 2 (V\u003csub\u003eR\u003c/sub\u003e, 3.3 km/s) that occurred on low-angle, blind, pure thrust (NW-SE)/oblique left-lateral thrust (NE-SW) faults with centroid depths of 12-10 km, respectively, along a fault length of 50 km (max) at a depth range of 3-16 km (max) (Figs. 2, 3 and 6);\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(b) the co-seismic off-fault deformation at a depth range of 7-10 km (max) implies long wavelength-low amplitude co-seismic surface folding, with a slip of 80 cm (max) along a length of ~50 km (Figs. 4-6); and\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(c) the co-seismic stress changes significantly load and activate the source fault planes of Eq 1 and Eq 2 and greatly influence along-strike strain distribution to NE (Fig. 7).\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003cspan style=\"text-align: inherit;\"\u003eThe on-fault/off-fault triggering that extended from SW to NE through shallow (\u0026lt;\u0026thinsp;10 km) and deep (\u0026gt;\u0026thinsp;10 km) sections (Figs. \u003c/span\u003e\u003cspan class=\"InternalRef\" style=\"text-align: inherit;\"\u003e8\u003c/span\u003e\u003cspan style=\"text-align: inherit;\"\u003e and \u003c/span\u003e\u003cspan class=\"InternalRef\" style=\"text-align: inherit;\"\u003e9\u003c/span\u003e\u003cspan style=\"text-align: inherit;\"\u003e) suggested coupled and decoupled interaction of the co-seismic stress variations through both source fault planes of Eq.\u0026nbsp;1 and Eq.\u0026nbsp;2 toward the NE. Coulomb failure stress coupling and decoupling phases through various depths are interpreted as indicating coupled and decoupled co-seismic deformations.\u003c/span\u003e\u003c/p\u003e\n \u003cp\u003eIn the following sections, we briefly review the major results of previous research and discuss the key implications of our study, with specific reference to: (i) the relationship between the 2005 Qeshm, 2006 Fin and the Bandar Abbas earthquakes; (ii) the presence of the co-seismic surface folding; (iii) decoupled seismic deformation and its implications for thick-skinned versus thin-skinned deformation, together with rapid and oblique propagation of co-seismic deformations driven by a triggered and activated basal d\u0026eacute;collement salt horizon over a wide area; and (iv) tectonic significance of the rupture decoupling process.\u003c/p\u003e\n \u003cp\u003eCentroid depths of 10\u0026ndash;12 km for the Bandar Abbas mainshocks suggest ruptures in the basement and/or the lower part of the sedimentary cover (e.g., Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e), and co-seismic slips are unlikely to have affected the surface (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea). Similarly, the 2005 Qeshm and 2006 Fin earthquakes occurred in the sedimentary cover, rather than the basement, but their centroid depths appear to be near to the depths where the cover and basement meet (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). In the SFB, given the 30-60\u003csup\u003eo\u003c/sup\u003e dips of most of the reverse faulting events, most of the earthquakes not only rupture the sedimentary cover, but also nucleate within it (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Thus, the Qeshm, Fin and Bandar Abbas earthquakes may be the best examples of this phenomenon.\u003c/p\u003e\n \u003cp\u003eLow-angle thrusting, consistent with the source mechanisms of the Bandar Abbas mainshocks, seems to have had a major effect in some areas in the SE-Zagros (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). The fault-plane solutions of regional earthquakes suggest several low-angle thrust faulting mechanisms, consistent with teleseismic focal mechanisms (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e) with optimal accuracy at depths of 10\u0026ndash;20 km and an estimated centroid depth error of \u0026plusmn;\u0026thinsp;2 km (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e), while reverse faulting earthquakes have centroid depths of 4\u0026ndash;20 km (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). Scattered, low-angle thrusts occurred at centroid depths of 5, 14 and 17 km in and around the Dezful Embayment and the deeper cut-off suggested by microseismicity is largely at 20 km or more (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). At Fin there have been many events at 20\u0026ndash;30 km depth, while well-resolved hypocentral depths were as much as 35\u0026ndash;40 km at Minab (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). Earthquakes occurring at \u0026gt;\u0026thinsp;20\u0026ndash;23 km and up to around 28 km are consistent with slip on shallow, N-dipping planes where the Arabian basement thrusts under the Eurasian plate (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"Section3\" id=\"Sec13\"\u003e\n \u003ch2\u003e4.4.1. The 2005 Qeshm and 2006 Fin earthquakes\u003c/h2\u003e\n \u003cp\u003eGentle symmetrical folds are usually associated with detachment folding. The Qeshm and Fin earthquakes occurred in such an area (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). Basement faulting may have given rise to the few earthquakes with centroid depths of \u0026gt;\u0026thinsp;15 km (e.g. Jackson \u003cspan class=\"CitationRef\"\u003e1980\u003c/span\u003e; Maggi et al. \u003cspan class=\"CitationRef\"\u003e2000\u003c/span\u003e; Talebian and Jackson, \u003cspan class=\"CitationRef\"\u003e2004\u003c/span\u003e; Hatzfeld et al. \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). This suggests a seismogenic layer of \u0026sim;20 km thick, consistent with ~\u0026thinsp;25\u0026ndash;30 km at Kermanshah, Fin and Khurgu (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eThe Qeshm mainshock-aftershock sequence\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe Qeshm Mw 6.0 reverse faulting earthquake at 10:22 UTC on 27 November 2005 had no associated surface rupture (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2007b\u003c/span\u003e). The centroid depth range was estimated at 6\u0026ndash;10 km (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2007b\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Fox et al., \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e). Aftershocks largely occurred at 14\u0026ndash;16 km below the slip range, accompanied by a swift decline in the number of earthquakes in the cover (Yaminifard et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e; Nissen et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). The mainshock ruptured the \u0026ldquo;Competent Group\u0026rdquo; and triggered basement microseismicity beneath the Hormuz salt layer (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Aftershocks were associated with both positive Coulomb stress changes imparted by the mainshock (up to 0.05 MPa) and areas where there had been negative stress changes (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e; \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eThe Fin mainshock-aftershock sequence\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe Fin earthquake occurred near the town of Fin, N-Qeshm Island, at 07:29 UTC on 25 March 2006, with E-W striking reverse faulting with a moment magnitude in the range of 5.7\u0026ndash;5.9 immediately followed by four aftershocks (Mw 5.5, 5.2, 5.0, 4.9) (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). The top and bottom of the rupture were well resolved at 5\u0026ndash;6 km and 9\u0026ndash;10 km respectively, consistent with 8 km depth and the largest aftershock (09:55 UTC) was modeled, yielding a centroid depth of 4 km (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Approximately 400 aftershocks between magnitudes Mw 1.0 and 4.0 were also recorded in the Fin area (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Focal depths were concentrated within the basement with a small peak in aftershock numbers at 14\u0026ndash;15 km and a larger one at 20\u0026ndash;25 km (Roustaei et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Gholamzadeh et al., \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e; Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe Qeshm and Fin mainshocks, together with the distributional patterns of their aftershock sequences, reveal almost the same centroid depth structure of earthquake faulting to the Bandar Abbas mainshocks in SFB. The Qeshm, Fin and Bandar Abbas mainshocks-aftershock sequences are located within the middle-lower sedimentary cover at depths where their mainshock co-seismic slips are shallower than most of the observed aftershocks (see Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e for details) (A-B profile in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e, E-F and G-H profiles in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e). The main reason for this phenomenon is that Eq. 1 and Eq. 2 broke strong barriers between two weaker faults upon which stresses were not sufficiently raised to induce aftershocks (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). For example, as observed in the C-D profile in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e and as reported by Nissen et al., (\u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e), several weak-soft layers within the thick sedimentary cover may have had a \u0026ldquo;dampening effect\u0026rdquo; on the distributional pattern of aftershock activity at the top and the bottom of the mainshock fault plane (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe aftershocks of the Bandar Abbas mainshocks that distributed at a full depth range of ~\u0026thinsp;5\u0026ndash;20 km from top to bottom, appear to be distinctly concentrated at a depth range of ~\u0026thinsp;10\u0026ndash;15 km (Figs. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e), while most of the aftershock focal depths at the Qeshm event occurred at a depth range of ~\u0026thinsp;13\u0026ndash;16 km consistent with the depth of the weak Hormuz salt in the SE-coastal Fars Arc (Jahani et al. \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e; Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Although the Hormuz salt is unable to host these aftershocks at such depths (~\u0026thinsp;10\u0026ndash;16 km) due to the increasing temperature of ~\u0026thinsp;200-400\u003csup\u003eo\u003c/sup\u003eC (e.g. Franssen and Spiers, \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e; Marques et al., \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e; Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e), the Hormuz salt can flow along the basement-cover interface due to co-seismic strain of the overlying competent cover (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e), while the lowermost competent cover is considerably strained but without rupturing. Eventually, the flow of the Hormuz salt, activated by the 2005 Qeshm mainshock, triggered a total of eight aftershocks (Mw 5.0\u0026ndash;6.0, from June 2006 to July 2009), which have shallow centroid depths of 4\u0026ndash;11 km and are located within the cover (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Similarly, in the case of the Bandar Abbas mainshocks, shallow depths of triggered aftershocks are located at a depth range of ~\u0026thinsp;5\u0026ndash;10 km within the cover (Figs. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv class=\"Section3\" id=\"Sec14\"\u003e\n \u003ch2\u003e4.4.2. Co-seismic surface folding\u003c/h2\u003e\n \u003cp\u003eAs illustrated in Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea-e and interpreted in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the up-dip limit of co-seismic slip of the Bandar Abbas earthquakes occurred at depths of \u0026sim;3\u0026ndash;7 km, while the down-dip limit of the ruptures occurred at depths of \u0026sim;10\u0026ndash;16 km. However, there were no surface ruptures associated with the Qeshm and Fin earthquakes, as the up-dip limit of slip occurred at depths of \u0026sim;3\u0026ndash;5 km and the base of the ruptures was consistent with the depth of the Hormuz salt (\u0026sim;8\u0026ndash;10 km), which are not estimated centroid depths according to Nissen et al., (\u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e) and shallower than our depth range of \u0026sim;10\u0026ndash;16 km. The reason is that Eq. 1 cuts the basement up to 16 km (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) and that the weak salt layer prevented slip propagation by forming a barrier at the base of the sedimentary cover (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe up- and down-dip limits of these rupture depths suggest that moderate-sized earthquakes (\u003cem\u003eM\u003c/em\u003ew 5\u0026ndash;6) may originate in the lower sedimentary cover associated with asymmetric surface folding (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). The ENE-trending area uplifted during the Fin earthquakes is oblique to the overlying E-W-trending fold axes, while the Qeshm earthquakes ruptured a SSE-dipping fault, perpendicular to the overlying anticline axis (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). In both cases, and as also seen in the Bandar Abbas earthquakes (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e), the causative faulting and the overlying folding above a low-angle thrust structure are closely connected (Eq. 2 in Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) due to the fault plane parallel detachment surface (7\u0026ndash;10 km) in the cover, as also reported by Nissen et al., (\u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). These results are strong evidence to suggest that surface anticlines in these epicentral areas are resulted from detachment folding, rather than from forced folding above discrete thrusts (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). The predominant mechanism resulting in surface fold generation in other regions of open, symmetric folding across the SFB is assumed to be detachment folding but forced folding also occurs in some areas (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eFurther observations from earthquakes that occurred in 1972 and 1977 are very similar to or the same as the Bandar Abbas earthquakes. The 1972 Ghir earthquake (Mw \u0026sim;6.7 and centroid depth of \u0026sim;9 km) (Baker et al. \u003cspan class=\"CitationRef\"\u003e1993\u003c/span\u003e) and the 1977 Khurgu earthquake (Mw\u0026thinsp;~\u0026thinsp;6.7 and a centroid depth of \u0026sim;12 km) (Nowroozi et al. \u003cspan class=\"CitationRef\"\u003e1977\u003c/span\u003e; Jackson and Fitch \u003cspan class=\"CitationRef\"\u003e1981\u003c/span\u003e), with diffuse small aftershocks at a depth range of 4\u0026ndash;22 km (Nowroozi et al. \u003cspan class=\"CitationRef\"\u003e1977\u003c/span\u003e), involved both cover and basement and ruptured through the boundary between these two layers (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e), which is consistent with Eq. 1 and Eq. 2. Both events occurred near strongly asymmetric anticlines at the surface, allowing significant changes in stratigraphic level (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). These asymmetric anticlines are different from the usual gentle symmetrical folds evident in most of the SFB (e.g., the source area of the Fin earthquakes in Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). At the epicentral area of the Fin event, earthquakes are limited to moderate magnitudes (\u003cem\u003eM\u003c/em\u003ew \u0026sim;6.0) because of the structurally weaker (incompetent) layers and also decouple surface folding from the reverse faults present in the lower levels of the cover (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). Co-seismic surface folding of the Ghir, Khurgu and Fin events is observed in particular locations, such as the frontal MFF (27.5\u003csup\u003eo\u003c/sup\u003eN-52.5\u003csup\u003eo\u003c/sup\u003eE) and the NE-Fars Arc (27.7\u003csup\u003eo\u003c/sup\u003eN-55.5\u003csup\u003eo\u003c/sup\u003eE) (Leturmy et al. \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e), where large fold-related earthquakes may be generated, consistent with the significant seismic hazard in the SFB (Leturmy et al. \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe Bandar Abbas mainshocks, in a similar fashion to the Qeshm, Fin, Ghir and Khurgu mainshocks, ruptured the middle-lower part of the cover at approximately 10\u0026ndash;12 km (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea). Based on the estimated centroid depths in the Fin area (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e), the proposed Hormuz salt layer ranges between ~\u0026thinsp;10 km and ~\u0026thinsp;12 km depth in the Bandar Abbas area and this is closely coincident with our depth ranges. This indicates that Eq. 2 and Eq. 1 ruptured the top (cover) and bottom (basement) sections of the salt horizon, respectively. Accordingly, the Bandar Abbas aftershock sequence, ranging from ~\u0026thinsp;5 to ~\u0026thinsp;20 km depths, was concentrated both within the cover (~\u0026thinsp;5\u0026ndash;10 km) and also the basement (~\u0026thinsp;13\u0026ndash;20 km, up to ~\u0026thinsp;25 km) (Figs. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e). Triggered aftershocks possibly represent breaking up of neighboring strata as the activated salt flows through the depth range of ~\u0026thinsp;10\u0026ndash;12 km due to co-seismic strain at the base of the cover. This strongly suggests that most of the moderate earthquakes within the SFB occur within the \u0026ldquo;competent group\u0026rdquo; of carbonate sediments that make up the middle-lower parts of the cover (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eLast but not least, the Bandar Abbas earthquakes, with the Qeshm, Fin, Ghir and Khurgu earthquakes, are perhaps the best examples of activated salt flow-induced moderate earthquakes nucleating within a carbonate sequence (Eq.\u0026nbsp;2) anywhere in the SFB and generating surface expression of earthquake-related detachment folding (7\u0026ndash;10 km) parallel-subparallel to the salt d\u0026eacute;collement layer (~\u0026thinsp;10\u0026ndash;12 km).\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec15\"\u003e\n \u003ch2\u003e4.5. Decoupled seismic deformation; thick-skinned versus thin-skinned deformation\u003c/h2\u003e\n \u003cp\u003eIn the SFB, most of the earthquakes occur within the lower sedimentary cover (~\u0026thinsp;10\u0026ndash;14 km), with smaller events at depths of up to \u0026sim;20\u0026ndash;30 km with occasional larger events at depths of up to \u0026sim;20 km (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e). Most seismic strain appears to be released at depths of ~\u0026thinsp;5\u0026ndash;10 km, supported by teleseismic centroid depths, and this is much less likely to occur at depths of ~\u0026thinsp;10\u0026ndash;20 km, but there is evidence for this in the form of several moderate-sized earthquakes. Seismic moment release at a depth range of ~\u0026thinsp;5\u0026ndash;20 km, consistent with the Bandar Abbas mainshock-aftershock sequence depth range, suggests aseismic shortening of the Zagros basement (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eIn order to provide quantitative values of shortening and to understand the mechanisms of deformation accommodation in the SE-Zagros, Molinaro et al., (\u003cspan class=\"CitationRef\"\u003e2004\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003ea) constructed cross-sections projected on SFB (Regard et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). In the SE-Zagros, the Bandar Abbas-Hadjiabad section (see the cross-sectional BB\u0026rsquo; profile shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e of Regard et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e) there are two markedly different N-S shortening values, ~\u0026thinsp;10 (4.5% ratio) for the basement and ~\u0026thinsp;45 km (22% ratio) for the cover (Regard et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). This large discrepancy implies a complete \u0026ldquo;decoupling\u0026rdquo; of shortening in the two layers, as reported by Molinaro et al., (\u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). It has been suggested that deformation in the cover was increased by the effect of the ductile Hormuz evaporites, while shortening was reduced in the basement by thrusting (Regard et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). The discrepancy also indicates the two main stages in the evolution of the SFB; thin-skinned deformation with a d\u0026eacute;collement at depth of ~\u0026thinsp;8\u0026ndash;9 km during the Mio-Pliocene stage and thick-skinned deformation with a basement through major thrust faults from the Pliocene to the recent shortening stage, inferred from focal mechanisms (Nissen et al., \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e) and the general topography and structural elevation of the Zagros mountains (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e; Regard et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"Section3\" id=\"Sec16\"\u003e\n \u003ch2\u003e4.5.1. Basal salt d\u0026eacute;collement\u003c/h2\u003e\n \u003cp\u003eAn intersection at oblique angles between the fault planes of Eq. 1 and Eq. 2 (between shallow-seated cover folding and deep-seated basement thrusting in Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) led to a discussion of thick-/thin-skinned earthquake faulting, recognizable in the Bandar Abbas area (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e), where the faults arise through the cover and obliquely cut the folding (e.g., in the Kuh-e-Khush), due to a number of possibly mechanisms including fold rotation, reactivation of pre-existing structures or stress rotation (Regard et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eIn the Bandar Abbas earthquakes, as discussed above, the co-seismic deformation involved major low-angle thrusting in the basement (3\u0026ndash;16 km) with folding in the cover (7\u0026ndash;10 km) controlled by the basal Hormuz salt layer (~\u0026thinsp;10\u0026ndash;12 km) (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). The folding is constrained by detachment at a depth range of 7\u0026ndash;10 km (Eq. 2), without basement deformation. Thus, we consider that decoupled co-seismic deformation for the Bandar Abbas setting with mechanical stratigraphy describes the deformation pattern of basement thrust structures (Eq. 1) well by characterizing related, shallow, fold-thrust structures arising from similar origins (Eq. 2 and in the central Tarim craton, NW-China, by Chen et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). With specific reference to stratigraphically decoupled deformation characterization, as proposed by Chen et al., (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e), the salt layer that has low strength and Young\u0026rsquo;s modulus values compensates for co-seismic strain, mainly through lateral thickness changes (Chen et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). Thus, the salt flow thins in the subsiding areas but thickens in the folding areas, while co-seismically activated. This propagation mechanism is detailed in the following text.\u003c/p\u003e\n \u003cp\u003eSubsequent thrusting-folding caused by the Bandar Abbas earthquakes remobilizes the Hormuz salt, causing it to flow from an area of subsidence (~\u0026thinsp;0 km-thick beneath syncline due to its downwarping) toward an area of folding (~\u0026thinsp;1\u0026ndash;2 km-thick in the core of the anticline) (Edgell, \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e), consistent with a typical style of detachment folding (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) (e.g., Colman-Sadd, \u003cspan class=\"CitationRef\"\u003e1978\u003c/span\u003e; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2004\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). The detachment folding is due to the presence of significant structural differences between the sedimentary units involved in the folding process (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e), consisting of a basal incompetent layer acting as a detachment zone (salt/shale) overlain by a thick competent unit (carbonates) (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). Thus, the Hormuz salt acts as a basal d\u0026eacute;collement, allowing the deformation to propagate around 50 km to the NE (at least\u0026thinsp;~\u0026thinsp;50 km in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) (Davis and Engelder, \u003cspan class=\"CitationRef\"\u003e1985\u003c/span\u003e; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). Depletion of the salt at the base of the subsidence, effectively welding the basement and cover together, then favors the progressive propagation of thrusting through the forelimb (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). In Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the fault plane of Eq.\u0026nbsp;2 corresponds to an upper flat (7\u0026ndash;10 km) region accommodating shortening that, in the SW, has arisen from the lower levels of the cover. This is crosscut by the fault plane of Eq.\u0026nbsp;1 (3\u0026ndash;16 km) originating from basement thrust.\u003c/p\u003e\n \u003cp\u003eWe consider the upper flat (Eq.\u0026nbsp;2) to be associated with \u0026ldquo;fault-bend-folds\u0026rdquo;, as observed by Molinaro et al., (\u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e), transferring maximum displacement (80 cm in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea) from a lower flat (10 km) likely in the Hormuz salt layer (~\u0026thinsp;10\u0026ndash;12 km) to an upper flat (7 km) (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). This shortening, transmitted into the cover, allowed the deformation front to extend into the upper flat in the NE, causing the cover to form a series of relatively small detachment folds, parallel-subparallel to basal salt d\u0026eacute;collement at ~\u0026thinsp;10 km depth.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv class=\"Section3\" id=\"Sec17\"\u003e\n \u003ch2\u003e4.5.2. Obliquity of salt deformation related to stress transfer\u003c/h2\u003e\n \u003cp\u003eThe vectored sum of maximum co-seismic slips of the NW-SE striking pure thrusting (30 cm) in the basement (Eq. 1) and the NE-SW striking oblique thrusting (80 cm) in the cover (Eq. 2) (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea and b) are ~\u0026thinsp;85 cm (max) directed to N, indicating a relatively slight rotational motion of the hanging wall block toward the NE (clockwise rotation), in which the detachment folding occurs (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). Such a deflection of the detachment folds, located on the hanging wall, indicates the passive draping of the cover which has accommodated the vertical uplift along the fault (Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eBilateral rupture source characteristics and the oblique left-lateral thrust focal with a little strike component (Eq. 2) shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea may be due to the effect of the strike-slip movement in the salt d\u0026eacute;collement on the cover (as also proposed by Ricou \u003cspan class=\"CitationRef\"\u003e1974\u003c/span\u003e; Hessami et al. \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e; Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e), such as when the salt layer is obliquely oriented to the shortening direction. The weakness of the salt layer easily favors maximum lateral propagation (~\u0026thinsp;85 cm) to the N and rotation of detachment folds toward NE, thus localizing deformation in a distinct trend to the NE and generating relatively little left-lateral strike-slip component in the cover, which is required to generate the bending of the small folds (Callot et al., \u003cspan class=\"CitationRef\"\u003e2007\u003c/span\u003e; Jahani et al., \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e; Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). Maximum co-seismic slip (30 cm) along pure thrusting in the basement (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea) is not sufficient to completely overprint the folding that exhibits a deflection oblique to the salt d\u0026eacute;collement (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eIn the E-arm of the SFB, particularly around the Bandar Abbas area, the majority of folds frequently display such distinct deflections in a trend toward a NE-SW orientation, such as the Shab anticline (Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). The Kuh-e-Muran is, perhaps, one of the best structures, being surrounded by salt plugs and associated with an initial NE-SW salt wall that controls the position of the structure (Jahani et al., \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e; Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). This has been interpreted as activation of a NE-SW basement reverse fault running parallel to the Kuh-e-Muran structure that has elevated the earlier folds on its hanging wall (Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). Similarly, an ENE-WSW trending Kuh-e-Khush structure, linked to the HZF and superimposed over the NW-SE trend of an early fold, has also been proposed to be related to a basement fault (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e; Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). Low-angle thrust faults cutting obliquely through the detachment folds (Eq. 2) with a salt layer controlling the fold geometry, as in the Kuh-e-Muran structure (Jahani et al., \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e) is also proposed by Molinaro et al. (\u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e) for the Kuh-e-Khush structure and is consistent with the geological and morphological data and focal mechanisms recorded in the area (Leturmy et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eAs inferred from cross-sectional depth profiles projected on the fault plane of Eq. 2 (shown in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e) and co-seismic slip pattern of Eq. 2 (shown in Figs. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e), our interpretation is that the salt most probably propagates through the basement-cover interface at a depth range of ~\u0026thinsp;10\u0026ndash;12 km toward the NE. We infer that this propagation appears to be prominent in a few profiles, along which co-seismic stress changes are decoupled and co-seismic slips are large. For example, the salt flow seems to propagate along the C-D profile in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e with large co-seismic slips (~\u0026thinsp;40 to ~\u0026thinsp;60 cm in the central part of the rupture along the C-D profile), in which stress changes are decoupled. However, the salt flow is only partly observable in the A-B profile, where stress changes are only partly decoupled and co-seismic slips substantially decrease in a range of ~\u0026thinsp;0\u0026ndash;20 cm (the up-dip limit of the rupture along the A-B profile). This may be valid for the E-F profile (down-dip limit of the rupture), along which salt flow is partly clear with small co-seismic slips (~\u0026thinsp;0\u0026ndash;10 cm) and decoupled stress changes. We propose that the presence of the salt flow, parallel/subparallel to the fault plane of Eq. 2 (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e), considerably controls, distributes and/or accelerates the co-seismic slips of Eq. 2, and also Eq. 1 during its relatively rapid propagation toward NE. We suggest that this is, in fact, the main cause of the bilateral rupture sources of both earthquakes (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea). In doing this, the salt activates and drives co-seismic stress transfer and redistributes the high-to-low/low-to-high stress changes.\u003c/p\u003e\n \u003cp\u003eFinally, the fold deformation front, propagating toward NE with wavelengths in the region of tens of kilometers (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e), is needed to accommodate deformation of the basement (e.g., Mouthereau et al., \u003cspan class=\"CitationRef\"\u003e2007\u003c/span\u003e; Malekzade et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e). This implies \u0026ldquo;synchrony\u0026rdquo; between thin- and thick-skinned deformations (Hatzfeld et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Malekzade et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e), consistent with seismic and GPS measurements (Masson et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e; Malekzade et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec18\"\u003e\n \u003ch2\u003e4.6. Tectonic implications for the rupture decoupling process\u003c/h2\u003e\n \u003cp\u003eLow-angle, blind thrust deformations in the Bandar Abbas source area imply that two steps of well-known deformation can be distinguished within the area. In the case of Eq.\u0026nbsp;2, shortening is accommodated within the cover both by low-angle thrusting and by large-scale folding, consistent with thin-skinned cross-sections of Molinaro et al., (\u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). In the case of Eq. 1, major out-of-sequence basement thrusts with strong seismicity records cut through the overlying structures of the cover (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e), consistent with the thick-skinned cross-sections of Molinaro et al., (\u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e), which illustrate that a thrust fault linked to a deep basement ramp cuts the fold at an oblique angle (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). This is consistent with previous suggestions that large thrust faults with significant displacement cut through both basement and cover (Blanc et al., \u003cspan class=\"CitationRef\"\u003e2003\u003c/span\u003e; Alavi, \u003cspan class=\"CitationRef\"\u003e2007\u003c/span\u003e; Verg\u0026eacute;s et al., 2011; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). The Eq. 1 and Eq. 2 mainshocks in the Bandar Abbas area are, therefore, the clearest examples of the rupture decoupling process exhibiting slip distribution geometry of thick-skinned and thin-skinned co-seismic deformations (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). Both earthquakes support and confirm successive thin-skinned and thick-skinned deformation, such as the Jain, Faraghun, and Kuh-e-Khush structures reported in Molinaro et al. (\u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eSource mechanisms of both earthquakes reveal that the thick-skinned mainshock (Eq. 1) initially ruptured at approximately the depth level of the bottom of the salt (~\u0026thinsp;12 km) and rapidly mobilized the Hormuz salt at the same depth, then rapidly triggered and activated the thin-skinned mainshock (Eq. 2). Eq. 2 ruptured at approximately the depth level of the top of the salt (~\u0026thinsp;10 km) and generated the co-seismic detachment folds, similar to the very rapid propagation of deformation in similar settings described previously (Letouzey et al., \u003cspan class=\"CitationRef\"\u003e1995\u003c/span\u003e; Cotton and Koyi, \u003cspan class=\"CitationRef\"\u003e2000\u003c/span\u003e; Costa and Vendeville, \u003cspan class=\"CitationRef\"\u003e2002\u003c/span\u003e; Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). As observable in the STFs of Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, such a rapid propagation of ruptured, mobilized, triggered and activated successive deformations may have resulted from simultaneous activation of the basal d\u0026eacute;collement salt horizon and the detachment folding over a wide area (Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e), consistent with GPS data and seismic measurements (Hatzfeld et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Malekzade et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e; Masson et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). We consider that such shorter-term successive deformation activation requires a closer relationship and interaction of previously existing structures, including folds, detachments, and evaporates, over the same wide area (e.g., Molinaro et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eAs interpreted from rupture source areas of Eq. 1 and Eq. 2 at the Bandar Abbas location of the SFB, the fold-thrust belt is co-seismically deformed by large basement and cover thrusts with \u0026quot;ramp-flat\u0026quot; geometries as proposed by Verg\u0026eacute;s et al., (2011), where the thrust ramp in the basement is separated from the deformation front and located ahead in the sedimentary cover above flat segments of the same thrust. The ductile style (continuous and discretely distributed strain) of the salt accommodates most of the deformation in the incompetent shallow cover (Chen et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e), causing a lack of surface rupture and/or brittle failure. Thus, ductile shear facilitates the change from oblique thrust faulting in the cover to pure thrust faulting in the basement, vertical axis rotation and, perhaps, strain partitioning, but this concept is beyond the scope of this study. It is essential to note that, in the Bandar Abbas area with a weak deformation pattern, mechanical stratigraphy more effectively demonstrates its control on long wavelength surface folding, low-angle blind thrust faulting and the rupture decoupling process than expected (e.g., Asaoka et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e; Chen et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eFinally, the rupture decoupling is typical of fold-thrust belts where the cover-basement contact is extremely weak, such as in the Alps, the Betics and the Pyrenees (Verg\u0026eacute;s et al., 2011). The thin-skinned earthquake faulting events, as predominant seismic features of the SFB, are affected by larger wavelength processes of thick-skinned earthquake faulting events (Verg\u0026eacute;s et al., 2011), similar to the past stage of Himalaya, consistent with Hatzfeld and Molnar, (\u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e) and Malekzade et al. (\u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eCo-seismic slip distribution models consist of relatively fast rupture sources of Eq.\u0026nbsp;1 and Eq.\u0026nbsp;2 that occurred on a low-angle, blind, pure thrusting (NW-SE)/oblique left-lateral thrusting (NE-SW) in the basement-cover interface, with centroid depths of 12\u0026thinsp;\u0026minus;\u0026thinsp;10 km, along fault lengths of ~\u0026thinsp;40\u0026ndash;50 km, at depth ranges of 3\u0026ndash;16 km and 3\u0026ndash;15 km, respectively. Shallow off-fault deformation implies long wavelength-low amplitude co-seismic surface folding in the detached cover (at depths of 7\u0026ndash;10 km) with a maximum slip of 80 cm to NE. Coulomb stress changes load and trigger both fault planes in areas where faults are brought closer to failure, and influence along-strike co-seismic strain distribution to NE. The SW-NE trending on/off fault stress triggering through shallow (\u0026lt;\u0026thinsp;10 km) to deep (\u0026gt;\u0026thinsp;10 km) sections suggests coupled/decoupled interaction of the co-seismic stress variations along both fault planes, which indicate that stress decoupling propagating from the SW to the NE corresponds to the salt d\u0026eacute;collement (at depths of 10\u0026ndash;12 km).\u003c/p\u003e \u003cp\u003eThe weak salt layer, co-seismically ruptured and rapidly mobilized, compensates for co-seismic strain through lateral thickness changes; the salt flow propagates from the SW through the subsiding area to the folding area to the NE. The pure thrust faulting, with a maximum slip of 30 cm to NE, affecting both basement and cover (at depths of 3\u0026ndash;16 km), and occurring in a particular zone beneath the surface folding, obliquely disrupts the detachment in the cover and generates a single detachment level above the salt d\u0026eacute;collement. This indicates a clear association between causative faulting and overlying detached folding. Rupture decoupling for both events with mechanical stratigraphy can well describe the deformation pattern of basement thrust structure by characterizing the genetically related shallow fold-thrust structure. The Bandar Abbas earthquakes are thus the best examples of the rupture decoupling process that exhibits distinct co-seismic slip pattern geometry of the successive thick-/thin-skinned deformation styles. Thick-skinned Eq.\u0026nbsp;1 ruptured and mobilized the salt layer, then triggered and activated thin-skinned Eq.\u0026nbsp;2 that generated the co-seismic detachment folds, which the ductile salt accommodates in the shallow cover. Thus, basal ductile shear facilitates the change from pure thrust faulting in the basement to oblique thrust faulting in the cover. In the Bandar Abbas area, mechanical stratigraphy more distinctly demonstrates the control on long wavelength surface folding, low-angle blind thrust faulting, and the rupture decoupling process.\u003c/p\u003e \u003cp\u003eAnomalous interference patterns through superimposed fault planes of the Bandar Abbas earthquakes with a ductile salt horizon indicate that the thin-skinned faulting events are predominantly affected by larger wavelength processes of thick-skinned faulting events in the Bandar Abbas area of SFB. This has implications for the deformation chronology of the thick-/thin-skinned phases of Zagros orogeny.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe earthquake data used for teleseismic waveform modeling were downloaded from the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope proposal of the National Science Foundation under Cooperative Agreement EAR-1261681). We are grateful to the Editor in Chief and two anonymous reviewers for their valuable comments and suggestions that helped us to improve the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAdams, A., Brazier, R., Nyblade, A., Rodgers, A. and Al Amri, A., 2009. Source parameters for moderate earthquakes in the Zagros mountains with implications for the depth extent of seismicity, Bull. 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Letouzey (2005), Detachment folding in the Central and Eastern Zagros fold-belt (Iran): salt mobility, multiple detachments and late basement control, J. Struct. Geol., 27, 1680-1696, doi:10.1016/j.jsg.2005.05.010.\u003c/li\u003e\n \u003cli\u003eSt\u0026ouml;cklin, J., 1968. Structural history and tectonics of Iran: a review. Bull. Am. Assoc. Pet.\u003c/li\u003e\n \u003cli\u003eStoneley, R., 1990. The Arabian continental margin in Iran during the Late Cretaceous, Geol. Soc. Lond. Spec. Publ., 49, 787-795.\u003c/li\u003e\n \u003cli\u003eTalbot, C. J., and M. Alavi (1996), The past of a future syntaxis across the Zagros, in Salt Tectonics, edited by J. L. Alsop, D. J. Blundell, and I. Davison, Geol. Soc. Spec. Publ., 100, 89-109.\u003c/li\u003e\n \u003cli\u003eTalebian, M., 2003. Active faulting in the Zagros mountains of Iran, PhD thesis, University of Cambridge.\u003c/li\u003e\n \u003cli\u003eTalebian, M., and J. 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Geodynamics, 61, 138-147.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Co-seismic displacement, Finite-fault source inversion, Teleseismic P-waveforms, Rupture process, Décollement, Co-seismic stress change","lastPublishedDoi":"10.21203/rs.3.rs-2531086/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2531086/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe co-seismic properties of the \u003cem\u003eM\u003c/em\u003ew 6.0 (12:07:03 UTC) and \u003cem\u003eM\u003c/em\u003ew 6.4 (12:08:06 UTC) earthquakes that took place on 14 November 2021, Bandar Abbas Syntaxis, SE-Zagros Simply Folded Belt (SFB), Iran, are thoroughly examined. Understanding the earthquake ruptures and their relationship to the co-seismic deformations, critical to our knowledge about the earthquake source mechanisms, has provided a singular chance to interpret the details of the rupture procedure of these two interrelated earthquakes, to complement previous studies of seismicity. Here, using finite-fault source inversion, we first estimated the co-seismic source models and then the co-seismic displacements during the earthquakes, differentiated into vertical/horizontal components. We inverted the observed teleseismic broadband \u003cem\u003eP\u003c/em\u003e-velocity waveforms of the earthquakes to simultaneously estimate the finite-fault rupture process, the slip distribution, the fault geometry and the stress changes. We found that the earthquakes were typical blind thrust-fault types along NW-SE and NE-SW striking fault lengths of ~40-50 km, widths of ~25-30 km, at a depth range of ~3-16 km and ~3-15 km, respectively, with co-seismic surface folding (~7-10 km) to NE controlled by a salt décollement layer at a depth range of ~10-12 km. We also found that the earthquakes consisted of relatively fast rupture sources (V\u003csub\u003eR\u003c/sub\u003e 3.3 km/s); an initial pure thrust faulting bilateral rupture at a depth of 12 km with a maximum slip of 30 cm and a dip angle of 32\u003csup\u003eo\u003c/sup\u003e, which was followed by a bilateral rupture with an oblique-slip left-lateral thrust faulting at a depth of 10 km, with a maximum slip of 80 cm and a dip angle of 24\u003csup\u003eo\u003c/sup\u003e propagated towards the NE. The joint interpretation of estimated Coulomb stress changes imparted by proposed variable slip rupture models, and the salt layer indicated that the stress increased load, triggered the fault planes of both events and influenced along-strike co-seismic strain distribution, providing evidence for the SW-NE trending activation of the stress decoupling between the ruptures, corresponding to the salt décollement. The initial pure thrust motion ruptured and mobilized the salt layer, then triggered and activated the bilateral rupture that generated the co-seismic detachment folds subparallel to the décollement. The weak salt, co-seismically ruptured and rapidly activated, compensated for co-seismic strain through lateral thickness changes from SW to NE and obliquely accommodated the folding in the shallow cover. Thus, basal ductile shear facilitated the change from pure thrust faulting in the basement to oblique thrust faulting in the cover. This finding clarifies differences in rupturing properties and deformation styles of such low-angle thrust faults. Anomalous interference patterns through superimposed fault planes of the Bandar Abbas earthquakes with the salt horizon have illuminated the rupture decoupling process and stress changes of the successive thick-/thin-skinned earthquakes, typical of the Zagros SFB.\u003c/p\u003e","manuscriptTitle":"Decoupled co-seismic deformation and stress changes during the 2021 (Mw 6.0, 6.4) Bandar Abbas earthquakes, SE-Syntaxis of Zagros, Iran; New insights into the rupture decoupling process","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-02-01 19:36:28","doi":"10.21203/rs.3.rs-2531086/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-06-24T19:46:09+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-06-12T00:14:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"858e9cac-d9ba-4a6b-97de-ec9759c4a6a8","date":"2023-05-15T11:46:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-03-05T09:29:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-01-31T05:33:29+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-01-31T05:33:28+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Earth Sciences","date":"2023-01-30T19:14:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3dab4c60-7fa2-4b0b-8c06-a3d18b36b136","owner":[],"postedDate":"February 1st, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-30T15:07:50+00:00","versionOfRecord":{"articleIdentity":"rs-2531086","link":"https://doi.org/10.1007/s12665-023-11232-3","journal":{"identity":"environmental-earth-sciences","isVorOnly":false,"title":"Environmental Earth Sciences"},"publishedOn":"2023-10-26 15:02:32","publishedOnDateReadable":"October 26th, 2023"},"versionCreatedAt":"2023-02-01 19:36:28","video":"","vorDoi":"10.1007/s12665-023-11232-3","vorDoiUrl":"https://doi.org/10.1007/s12665-023-11232-3","workflowStages":[]},"version":"v1","identity":"rs-2531086","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2531086","identity":"rs-2531086","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}