Tectonic and Morphological Features of a Submarine Negative Flower Structure: In the Sinop Basin (Central Black Sea) and the Evaluation of Regional Seismic Hazard

Tectonic and Morphological Features of a Submarine Negative Flower Structure: In the Sinop Basin (Central Black Sea) and the Evaluation of Regional Seismic Hazard | 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 Tectonic and Morphological Features of a Submarine Negative Flower Structure: In the Sinop Basin (Central Black Sea) and the Evaluation of Regional Seismic Hazard Dr. SEVİNÇ ÖZEL FÜZÜN, Prof. Dr. GÜNAY Çifci, Prof. Dr. HASAN Sözbillir, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8779310/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The southern margin of the Eastern Black Sea is commonly regarded as a region of low seismicity, largely because onshore and offshore fault mapping remains limited. However, focal mechanism solutions from the last century indicate active normal and strike-slip faulting in addition to thrust earthquakes, with the reveal pronounced seismic clustering offshore of the Sinop Basin near Samsun. To investigate the origin of this seismotectonic complexity, approximately 1,300 km of high-resolution multichannel seismic reflection profiles were acquired, processed, and interpreted together with multibeam bathymetric data. This analysis addresses the long-standing debate on whether the basin represents a young foreland basin or a graben-type structure, and evaluates the present-day activity of basin-bounding faults. Fault geometries and their seafloor morphological expressions, particularly negative flower structures-provide key constraints on the regional seismotectonic framework. Four seismic units were identified and correlated with Upper Cretaceous–Paleocene, Eocene, Oligo–Miocene, and Plio–Quaternary successions. Faults that terminate above the Upper Cretaceous–Paleocene units are interpreted as inactive, whereas faults that cut all seismic units and reach the seafloor are considered active. Faults confined to the Plio–Quaternary unit are interpreted as syn-sedimentary. These results indicate that the Sinop Basin is not a passive depression but an actively deforming basin controlled by oblique to strike-slip faulting. The mapped active faults are capable of generating earthquakes with magnitudes of Mw ≈ 6.2–6.9, implying a significant seismic hazard for the central Black Sea region. Black Sea Sinop Basin Arkhangelsky Ridge active faulting negative flower structure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 1. Introduction Turkey is one of the most tectonically active regions on Earth, experiencing intense deformation as a result of the interaction between the Eurasian, Anatolian, Arabian, and African plates. The westward movement of the Anatolian Plate along the right-lateral North Anatolian Fault (NAF) and the left-lateral East Anatolian Fault (EAF), together with ongoing subduction and collision processes along the southern and northern margins of the country, control both terrestrial and marine tectonics (Kalafat, 2017 ; Softa et al., 2018 , 2021 ) (Fig. 1 ). The geological structure of the Black Sea has been under investigation since the publications of regional seismic lines for the entire area in the 1980's (Tugolesov et al.,1985; Finetti et al.,1988; Belousov et al., 1988, 1989). More recent seismic lines were shot in parts of the Black Sea and were published by Robinson et al. ( 1996 ), Dinu et al. (2005), Afanasenkov et al. (2007), Shillington et al. (2008), Rangin et al. ( 2002 ), Khriachtchevskaia et al. (2009, 2010), Munteanu et al. ( 2011 ), Menlikli et al. (2009), Stovba et al. (2009), Tari et al. (2009), Stuart et al. (2011), Nikishin et al. (2010, 2012), Mityukov et al. (2012), Almendinger et al. (2011), Georgiev (2012), TPAO/BP Eastern Black Sea Project Study Group (1997), Gozhik et al. (2010), Graham et al. ( 2013 ). In recent years, various petroleum companies have acquired a very large amount of 2D and 3D seismic data for individual blocks, though results of these operations are not published. As observed in the seismic lines presented in the study by Nikishin et al. ( 2015 ), the Andrusov Ridge clearly has a sedimentary cover of Cretaceous–Cenozoic age and also contains volcanic rocks from the Cretaceous period. In contrast, the seismic data over the Arkhangelsky Ridge do not indicate the presence of a thick Mesozoic cover. Within this framework, the Sinop Basin stands out as an important structural and seismotectonic feature, although its origin remains debated. Some researchers interpret the basin as a forearc basin formed by crustal flexure (Meredith and Egan, 2002 ), while others propose a transtensional graben model (Rangin et al., 2002 ). The Arkhangelsky Ridge, located north of the Sinop Basin and bordered by normal fault zones, is currently buried due to excessive sedimentation in the Black Sea (Dondurur and Çifçi, 2007 ). The researcher argued that none of these fault zones exhibit active faulting that reaches the seafloor, and therefore, the likelihood of earthquakes causing any displacement of the seafloor in these zones is considered very low. Especially, the neotectonic structures of the Black Sea coasts are not as active compared to other regions (İşcan et al., 2019). Additionally, the weak and sparse seismicity observed in the region defined as secondary neotectonic (Şengör, 1980) has not been associated with the main tectonic movements of Anatolia up to the present. The areas between the Black Sea coasts-particularly the tectonic lineaments forming the Central Black Sea Ridge-and the North Anatolian Fault Zone (NAFZ) have long been considered inactive (İşcan et al., 2019). On the other hand, our detailed observations from seismic sections and previous studies indicate that some of these faults do, in fact, cut through to the seafloor and cause significant strike- to dip-slip displacements (Kalafat, 2017 zün-Özel, 2024). It has been suggested that the basement of the two east-west oriented basins formed and influenced by the Arkhangelsky Ridge on the Central Black Sea High consists of thinned continental crust and/or oceanic crust (Belousov, 1988; Finetti et al., 1988 ; Yegorova et al., 2010; Yegorova et al., 2013; Graham et al., 2013 ). However, it is considered necessary to clarify whether this ridge continues to be shaped by active or inactive faults. The aim of this study, (1) detect the morphological features of focused area, (1) define the stratigraphic and structural framework of the basin, (2) classify and map faults located between Bafra (Samsun) offshore and the Central Black Sea Ridge, (3) reveal and regionally assess the submarine negative flower structure, (4) recalculate the potential earthquake magnitudes based on the length-magnitude relationships of the tectonic lineaments revealed in cross-sections, using the mathematical relations proposed by Wells and Coppersmith ( 1994 ). This study was carried out within the framework of the AlerT project (Anatolian Climate and Tectonic Hazards; Project Code: 607996) project. The ALeRT project was designed to investigate the uplift history of the Anatolian Plate, basin development, and the controlling tectonic mechanisms governing these processes. The project was conducted through a consortium comprising 11 academic institutions and 5 private companies, focusing primarily on onshore tectonic and climatic interactions across Anatolia. The marine component of the project in Türkiye was undertaken by Dokuz Eylül University, Institute of Marine Sciences and Technology, providing offshore geophysical data essential for integrating marine and terrestrial tectonic frameworks. In addition to its scientific objectives, ALeRT was structured as an Initial Training Network (ITN), aiming to enhance the research capacity of early-stage researchers by offering advanced training opportunities, fostering integration into established research teams, and supporting long-term academic and professional career development. 2. Regional Geology and Seismotectonic Setting The study area is located along the coast of Samsun, at the point where the Kızılırmak River meets the Black Sea, encompassing a significant portion of the Arkhangelsky Ridge, which extends across the central Black Sea (Fig. 1 b). To the south of the region, along the Sinop coast of Turkey, lies the Kızılırmak River, while the Yeşilırmak River is situated to the east. These two major rivers play a critical role in shaping the hydrological and geomorphological structure of the region. According to Popescu et al. ( 2015 ), the effects of the Kızılırmak and Yeşilırmak rivers on the seafloor are observed in bathymetric data as large submarine canyons. The branches of the Yeşilırmak submarine valley system extend over 100 km, and its drainage basin covers an area of approximately 3,600 km² (Jipa et al., 2020 ). This system exhibits a dendritic structure, resembling vein-like patterns, particularly in areas with gentler slopes (Fig. 8 ). In their deep seismic studies, Dondurur and Çifçi ( 2007 ) successfully mapped the submarine canyons of the Yeşilırmak system in detail, reporting a total length exceeding 120 km, of which approximately 60 km display a dendritic pattern. The Black Sea basin was shaped by an extensional tectonic regime during the Early Cretaceous and transitioned into a compressional regime due to the collision between the Eurasian and Arabian plates in the Early Eocene (Robinson et al., 1995 ; Spadini et al., 1996; Tari et al., 2000). Following this transition, regions along the Black Sea coast, such as the Pontides, the Caucasus to the east, Crimea to the north, and the Balkans to the west, were incorporated into a compressional tectonic system. The Eastern Black Sea Basin (EBSB), bounded by the Arkhangelsky Ridge, and the Western Black Sea Basin (WBSB) differ significantly in terms of their formation processes, tectonic orientations, and sedimentary thicknesses (Robinson et al., 1996 ; Shillington et al., 2008; Nikishin et al., 2015 ). Deep seismic data reveal that sedimentary sequences up to 12–14 km thick have accumulated in the basin from the Late Cretaceous to the present (Nikishin et al., 2015 ; Finetti et al., 1988 ). In the deepest parts of the basin, oceanic crust lies at approximately 10 km below thick sedimentary layers, whereas the coastal and ridge regions are composed of continental crust (Sosson et al., 2010; Anatoly et al., 2015; Yegrova et al., 2010). Multichannel seismic reflection-refraction, gravity, and magnetic data from the region reveal that the eastern and western basins both with oceanic crust exhibit distinct structural characteristics (Rangin et al., 2002 ; Dinu et al., 2005) (Fig. 3 ). Geological and geophysical evidence including offshore seismic reflection profiles (Finetti et al., 1988 ), coastal morphology (Meisner et al., 1995), onshore geology and morphology (Okay and Şahintürk, 1997), and recent seismic activity (Neprochnov and Ross, 1978) indicate that the compressional tectonic regime in the eastern Black Sea region remains active. In contrast, there is no significant evidence of compressional or extensional regimes in the southwestern Black Sea region. The ridge in the central Black Sea represents a zone of thinned continental crust, forming the northwestern boundary of the EBSB. This basin is underlain by oceanic crust and is covered by sediment layers less than 12 km thick. Unlike the western Black Sea, the ridges and basins in the eastern part are intersected by numerous faults (Finetti et al., 1988 ). These two sub-basins are separated by the Central Black Sea Ridge, bounded by the northwest–southeast trending Andrussov Ridge in the north and the Arkhangelsky Ridge in the south (Fig. 1 a). This ridge functioned as a structural barrier until the Oligocene–Early Miocene, after which it became a single depositional center, buried under younger sediments (Kazmin et al., 2000; Nikishin et al., 2015 ). Two major seismic belts influence the study area. The first is the North Anatolian Fault Zone (NAFZ), a prominent right-lateral strike-slip fault located near the coast (Fig. 2 a). The second involves the first seismological evidence of an active thrust structure along the southern coast. Focal mechanism solutions indicate the coexistence of thrusting and strike-slip faulting in the region (Kalafat, 2017 ). Between 2006 and 2015, moment tensor (CMT) solutions were obtained for earthquakes with M > 3.7 using broadband station data (Alptekin et al., 1985; HRV, 1977–2013; Kalafat, 1998). These solutions were computed using regional broadband velocity waveform data (Dreger, 2002; Sokos and Zahradnik, 2013). Only events recorded by at least four digital broadband seismic stations were analyzed. For events between 1968 and 2006, global datasets or published solutions were used. The focal mechanisms of events with M > 3.7 predominantly indicate north–south compression with a minor east–west component. 3. Material and Method To investigate the fault architecture and stratigraphic framework of the Sinop Basin, high-resolution multichannel seismic and multibeam bathymetric data were utilized. These datasets were collected during a marine survey aboard the R/V Koca Piri Reis, operated by the Institute of Marine Sciences and Technology at Dokuz Eylül University in 2015. The survey performed in the frame of the ALERT (Anatolian Plateau Climate and Tectonic Hazards) Project, funded by the European Union’s 7th Framework Programme (Project Code: 607996), which aimed to evaluate tectonic and climatic hazards across the broader Anatolian region. 3.1 Seismic Data Acquisition and Processing As the sole marine partner in the ALERT Project, Dokuz Eylül University acquired approximately 1300 km of multichannel seismic reflection, CHIRP sub-bottom profiling (which resolves shallow stratigraphy at high resolution), and multibeam bathymetric data (used to map seafloor morphology). The survey was conducted along a total of 17 lines 13 oriented NW–SE and 4 NE–SW using the R/V K. Piri Reis research vessel (Fig. 1 c). A 216 channel seismic recorder with a 1350 m digital streamer was used for the acquisition. The seismic source consisted of a GI gun with a volume of 45 + 105 inc³. Shot spacing was 25 m, with a sampling rate of 1 ms and a record length of 6000 ms. The data were processed at the Marine Geophysics SeisLab laboratory using Landmark Graphics ProMAX software and analyzed with Seismic Micro Tech’s Kingdom Suite software. 3.2. Bathymetry Data Multibeam bathymetry data were collected using the ELAC-SeaBeam 1050D system, with 50Hz transdusers, mounted on the hull of the R/V Piri Reis research vessel, belonging to Dokuz Eylül University’s Institute of Marine Sciences and Technology. The DM505 sensor, which detects and immediately corrects the vessel’s movement in all three dimensions during data collection, was also used. Echosounder system is designed to collect data in both deep and shallow waters and features 126 beams with a total scanning width of 153° when all beams are utilized. The instrument operates with a beam angle of 1.5 × 1.5˚ and the footprint varies between 13 and 40m. The collected data were also processed and edited using the Caraibes program and gridded with 100-m cell size for this area (Fig. 1 c). 3.3. Seismicity The study area and the earthquake epicenter locations along the Black Sea coastal zone were mapped in two separate groups: historical earthquakes and instrumental-period earthquakes. All earthquake records were obtained from the Historical and Instrumental Earthquake Catalog available on the official website of the Disaster and Emergency Management Authority (AFAD). The spatial distribution density of historical earthquakes was classified based on intensity (I) into different categories, namely I < 6 and 6 < I 4 that occurred between 01 January 1900 and 01 January 2025 (Fig. 2 ). Earthquake maps were generated using the Geographic Information System (GIS)-based ArcGIS 10.8 software. To investigate the relationship between earthquake depth and seismicity, a 3D block model was constructed using earthquake data with magnitudes Mw > 1 and focal depths shallower than 40 km (Fig. 3 ). The model was generated using QGIS software. The geodetic parameters adopted for the study area are the Universal Transverse Mercator (UTM) projection, Zone 36N, and the World Geodetic System 1984 (WGS84) datum. 3 .4 Potential Earthquake Magnitude Calculation Formulations for estimating maximum earthquake magnitudes on fault segments have been derived based on empirical relationships between magnitude, rupture length, rupture width, rupture area, and surface displacement (Emre et al., 2016). In assessing the seismic potential of active tectonic structures in the study area, empirical relationships based on surface rupture length are among the commonly used methods. Four different formulas have been proposed for estimating the potential for possible earthquake generation: Utsu and Seki (1954), Wells and Coppersmith ( 1994 ), Ellsworth (2003), and Christophersen and Smith (2000). However, considering the surface rupture and fault types present in the region, the formulation developed by Wells and Coppersmith ( 1994 ), which covers all fault types, was selected as the most appropriate and is presented below: M = 4.86 + 1.32 x log(SRL) (1) in the Eq. (1), M and SRL represents the moment magnitude (Mw) and denotes the surface rupture length (in kilometers), respectively. This relationship was developed and applied based on surface rupture data from numerous historical and instrumental earthquakes, covering normal, reverse, and strike-slip fault types (REF). Due to its empirical nature, the maximum moment magnitude that a tectonic structure with a known fault length can produce can be estimated through this formulation. Such estimates are of great importance for seismic hazard analyses, engineering geology studies, and the development of earthquake scenarios (Bonilla et al., 1984; Ulusoy et al., 2004; Wesnousky, 2008; Irsyam et al., 2020; Cremen and Galasso, 2020; Gürboğa et al., 2024). However, it should be noted that this relationship is empirical and relies solely on surface rupture length, independent of the geometric and kinematic characteristics of the fault. Therefore, it is recommended to evaluate its applicability in different tectonic regimes before use. 4. Results 4 .1 B athymetry Map According to bathymetry data, the water depth within the study area is between 50 and 2000 m. The shelf break lies at approximately 200 m, while the Arkhangelsky Ridge is located at a depth of approximately 300 m. After the Arkhangelsky Ridge, it joins the deepest part of the Black Sea, which has an almost ideally flat bottom. On the onshore part of the study area, it is observed that the deep valleys of the Kızılırmak and Yeşilırmak rivers were formed on the shores of Sinop and Bafra, respectively. At the same time, it is observed that these rivers flow into both the central Black Sea ridge and the Sinop Graben and become a single channel towards the NW. In addition, a total of four submarine channels are identified within the study area, which merge to form a larger and wider U-shaped channel. The study also revealed the existence of a second submarine channel, trending NNE-SSW, connected to the Yeşilırmak submarine canyon. This channel extends northeastward, starting from the Kızılırmak River delta, and joins the Yeşilırmak channel. Bathymetric data also indicate that the Yeşilırmak submarine channel is the axial submarine canyon of the Sinop Basin, trending northwest. In Fig. 5, continental margin structures are evaluated based on the depth–slope graphs of Profiles 1–3 (Fig. 5a). Accordingly, Profile 1, located at the termination of the Arkhangelsky Ridge in the northern part of the study area, exhibits a relatively wide continental shelf, followed by the development of canyon/channel systems beyond the shelf break (Fig. 5b). In Profiles 1 and 3, the canyon structures appear to be more prominent, indicating enhanced erosional activity and sediment transport pathways along these sectors of the continental slope break (Fig. 5c-e). Two distinct submarine channel systems fed by the Yeşilırmak River are clearly identifiable on the seafloor based on multibeam bathymetric data (Özel Füzün et al. 2024). These channels display markedly different along-axis continuities, with the main channel extending for more than 120 km and a secondary channel reaching approximately 40 km in length, consistent with previous regional observations (Dondurur and Çifçi 2007; Özel Füzün et al. 2024). The secondary channel, which branches from the Yeşilırmak canyon and trends toward the mouth of the Kızılırmak River delta, has been identified through detailed morphometric analysis of multibeam bathymetric data and is interpreted as representing a paleochannel associated with the former course of the Kızılırmak River (Özel Füzün et al. 2024). The high sediment load supplied by the Yeşilırmak River facilitates the development and sustained activity of deep-sea fan systems, allowing the main channel to function as a major sediment transport pathway extending toward the central Black Sea basin (Dondurur and Çifçi 2007; Jipa et al. 2020). In addition, a third submarine feature characterized by a well-developed canyon morphology and related to the Kızılırmak River extends for approximately 44 km and is interpreted as a paleochannel based on its geomorphic configuration and stratigraphic context (Algan et al. 2002; Özel Füzün et al. 2024). These submarine channel and canyon systems become prominent approximately 15–20 km offshore of the Samsun coastline, coinciding with the transition from the continental shelf to the continental slope, where slope gradients increase and erosional processes intensify (Popescu et al. 2015; Özel Füzün et al. 2024). The evolution and activity of these channel systems are strongly influenced by the stratified hydrodynamic structure of the Black Sea, characterized by low-salinity surface waters overlying denser, anoxic deep waters (Jipa et al. 2020).During the Late Pleistocene (Würm glacial stage), a relative sea-level fall of approximately 120–150 m caused major rivers to discharge directly onto the continental slope, promoting canyon incision and enhanced downslope sediment transport (Lericolais et al. 2011).Sediment distribution within the canyons has been controlled by a combination of bottom-current activity, slope instability, and episodic turbidity currents, resulting in a complex internal sedimentary architecture (Dondurur and Çifçi 2007).The canyon floors are dominated by sandy to coarse-grained deposits associated with high-energy turbidity flows, whereas canyon walls and inter-canyon ridges are characterized by fine-grained, organic-rich hemipelagic sediments and locally developed sapropel layers (Dondurur and Çifçi 2007; Jipa et al. 2020).High-resolution seismic data further reveal the presence of shallow gas accumulations and gas-hydrate indicators within the sedimentary succession, particularly along canyon flanks and levee-like features (Dondurur and Çifçi 2007). The maximum water depth of the submarine canyon system reaches approximately 1450 m, while the Yeşilırmak-related channel networks are traceable within a depth range of 850–1700 m (Özel Füzün et al. 2024). Submarine extensions of both the Yeşilırmak and Kızılırmak river systems originate near the shelf edge and continue downslope between 850 and 1450 m water depths, merging at approximately 1450 m and extending basinward toward the basin plain, where their morphological influence gradually diminishes (Popescu et al. 2015; Özel Füzün et al. 2024).Paleochannel segments have been rapidly infilled by fine-grained sediments during Holocene sea-level rise, producing chaotic to discontinuous seismic facies and locally developed graded bedding observed in high-resolution seismic profiles (Algan et al. 2002; Özel Füzün et al. 2024). Table 1 . Morphometric characteristics of submarine channel systems related to the Yeşilırmak and Kızılırmak Rivers in the central Black Sea (based on multibeam bathymetric map, Fig. 3). Length and depth values are derived from the bathymetric data and supporting literature. The Yeşilırmak system is larger and more dendritic, while the Kızılırmak system is slightly smaller but of comparable depth extent. All values are cited from this study (Özel Füzün et al. 2024) and previous works (e.g. Dondurur & Çifçi 2007; Algan et al. 2002; Jipa & Panin 2020). Both canyon systems incise the continental shelf and extend from near the river delta mouths (tens of meters water depth) to the base of the continental slope (approximately 1.8–2.0 km deep) in the Sinop Basin. The Yeşilırmak canyon network has an overall length exceeding 120 km with extensive dendritic tributaries, whereas the Kızılırmak canyon is slightly shorter (over 90 km) and joins the Yeşilırmak system mid-slope. (Measurements based on Fig. 3 and data from Özel Füzün et al. 2024). Multibeam bathymetric data acquired from the Sinop Basin reveal the presence of a secondary, NE–SW trending paleo-channel that is morphologically linked to the Yeşilırmak submarine canyon. This configuration suggests that the modern canyon-channel system may not represent a stable, long-term sediment transport pattern, but rather records a reorganization of fluvial-to-marine sediment pathways across the continental shelf. 4.2 Seismic Units and Faults The seismic sections in project area were conducted along a total of 17 lines 13 oriented NW–SE and 4 NE–SW (Fig. 1c). In total, 1300km seismic profiles were interpreted and evaluated; however, the interpretations presented in this study focus on seismic lines with 2, 6, 8, 9, 10 and 11. During the stratigraphic interpretation of the seismic sections from the study area, four distinct seismic units were identified based on the structural characteristics of the region, seismic velocity data from the Central Black Sea Ridge (Finetti et al., 1988), and recent literature (İşcan et al., 2019). The oldest seismic unit is associated with the acoustic basement (U4). This unit generally exhibits undulating reflections that are subparallel to the seafloor. Overlying this, Unit U3 covers the U4 unit; however, its lateral continuity could not be fully traced across the region due to erosion or mass-wasting processes. Unit U3 has been interpreted as Eocene-aged strata. The overlying Unit U2, which blankets the U3 unit, is distributed more widely and represents a thicker sedimentary cover throughout the area. This unit consists of Oligocene–Miocene sediments and appears as a single, coherent seismic package. The uppermost and youngest unit, designated as U1, is separated from the underlying units by a distinct unconformity surface. Unit U1 is typically interpreted as progradational deltaic deposits that developed on and around the shelf break and the Arkhangelsky Ridge. This unit corresponds to the youngest sedimentary sequence deposited during the Pliocene–Quaternary period. In terms of thickness, Unit U1 reaches a maximum of approximately 0.75 s (two-way travel time) along Line 6, while Unit U2 attains about 0.5 s toward the northeastern termination of the Arkhangelsky Ridge. Additionally, the seismic sections reveal that in the shelf region—particularly along Lines 2 and 6—a well-defined shelf structure could not be observed. This is attributed to prolonged fluvial erosion near the coastal margins caused by river systems flowing seaward. The boundary of the acoustic basement observed in the seismic sections is neither continuous nor uniform, owing to its disruption by faults and its extension into deeper levels. In some profiles, this basal unit does not maintain downward continuity; instead, it locally rises upward, indicating displacement and offset resulting from faulting. Along the NE–SW-oriented seismic lines (Line 2, Line 6, Line 10, and Line 11) (Fig. 6-10), which are approximately perpendicular to the Central Black Sea Ridge, three distinct fault sets cutting across different depths and stratigraphic units have been identified. The tectonic structures are classified as follows: First group faults terminate within the upper portion of the acoustic basement and do not cut the overlying units. These faults are interpreted as structures that became inactive during the early Tertiary. Second group faults are located within Unit U1 but do not reach the seafloor. They are interpreted as syn-sedimentary faults, active contemporaneously with sedimentation. Third group faults are observed along the southwestern and northeastern margins of the Sinop Basin. The northeastern faults delineate the boundary between the Central Black Sea Ridge and the Sinop Basin, whereas the southwestern ones are located near the shelf break. These fault systems on both sides of the basin exhibit a converging geometry and collectively resemble a negative flower structure. Based on their characteristics, the third group faults are interpreted as active fault zones (Fig. 14). The Cretaceous-aged sedimentary basement, classified as the acoustic basement in the seismic sections, has been identified at a maximum depth of approximately 4 km within the study area. Toward the Arkhangelsky Ridge, the thickness of the overlying sedimentary cover decreases to about 1 km. The most significant tectonic structures identified in the region are the fault systems that delineate the southern boundary of the Central Black Sea Ridge and the Sinop Graben. The seismic packages spanning from the Eocene to the Pliocene–Quaternary have been displaced along these faults and uplifted in the profile, forming a graben-like geometry. In seismic line 11, the structure extending from the seafloor down to the acoustic basement is interpreted as a negative flower structure, typical of strike-slip fault systems (Fig. s 4 and 5). A closer examination of the ridge area reveals that the acoustic basement is well defined and overlain by three distinct stratigraphic units corresponding to the Eocene, Oligocene–Miocene, and Pliocene–Quaternary periods, each separated by prominent unconformity surfaces. Moreover, the stratigraphic succession atop the ridge differs in thickness from that within the displaced blocks, suggesting that the ridge units have undergone substantial erosion (Fig. 6). Within the region, several NW–SE-trending, oblique-to strike-slip dominated tectonic lineaments of varying lengths have been identified. Three of these lineaments are aligned along the Sinop coastal margin, while the others occur along the slopes shaping the morphology of the Arkhangelsky Ridge. As these tectonic structures are located within the Sinop Basin, they have been designated SB1–SB6. Faults SB1, SB2, and SB3 have been traced and interpreted along the NE–SW-oriented seismic profiles. These faults intersect small submarine channel structures and are characterized by offsets that extend up to the seafloor, indicating that they are active faults with a high potential for earthquake generation. On NE-SW direction of Lines 2 and 6, chaotic appearance with low reflectivity and irregular reflectors are identified at the river channel border. (Fig. s 6 and 7). These structures, are sliding material observed as a result of the giant mass movement downwards especially on higher slopes that limits the canyon structures, The sliding surface on which the sliding material slips is observed in Fig. 6e and 7. These structures appear on seismic sections as a continuous reflective surface that is smooth, horizontal, or slightly inclined due to the influence of in Line 2 (Fig. 6), the sliding material and the slip surface are observed together in the northern part of the Arkhangelsky Ridge. Another notable morphological feature in the region related to mass-movement processes is the presence of steep or inclined scarps formed at the initiation zones of these movements. In seismic Line 5, the structure observed at the upper boundary of the displaced mass has been identified as a head scarp (Fig. 5). This area exhibits a distinct break and steep surface, likely enhanced by the influence of faulting. Bathymetric mapping and seismic profiles from the study area reveal the presence of deep valleys incised by both active and paleo-fluvial systems. In the seismic sections, these features appear as deep depressions with laterally discontinuous and downward-inclined stratigraphic geometries, interpreted as submarine canyons or canyon floors. Two distinct canyon systems with differing depths and morphological characteristics have been identified, trending predominantly NE–SW, while a third canyon-like depression extends NW–SE, with depths ranging between approximately –900 m and –2000 m (Fig. 4). In the NE–SW-trending Line 17, which extends parallel to both the coastline and the Arkhangelsky Ridge, a relay ramp structure was observed at the northeastern boundary of the study area, formed above a fault interpreted as buried (Fig. 11). 4.3 S eismicity Data Analysis Analyses based on AFAD data, the distribution of earthquakes with Mw > 0 between 1900 and 2025 show that seismic activity is concentrated between the North Anatolian Fault Zone (NAFZ) and the coastal zone. (Fig. 2). Many earthquakes exceeding magnitude Mw>3 occurred in the study area. (Fig. 2). The depth distribution of these earthquakes indicates the existence of three separate and parallel fault segments with an uncertainty of depth approximately 35 km. Fig. 3). Although focal mechanism solutions are limited, a significant increase in the number of events detected has been observed since 2006 with the expansion of seismic stations. (Kalafat et al., 2005; Kalafat, 2017). Focal mechanism solutions are available for the earthquakes with magnitude Mw = 4.0 that occurred in the Sinop Basin in 2014 and 2025 (Fig. 2b). Epicentral analyses revealed that a distinct earthquake cluster occurred on the Arkhangelsky Ridge. The active fault segments identified along the northeastern and southwestern coastal margins of the Sinop Basin, based on interpretations integrating seismic profiles and bathymetric contours, range between 10 km and 40 km (Fig. 4). In the coastal area of Samsun, three active strike-slip fault segments trending approximately parallel to the shoreline have been identified. In addition, three oblique to strike-slip fault segments with an approximate NE–SW orientation have been mapped along the Arkhangelsky Ridge. Furthermore, these faults are estimated to be capable of generating earthquakes with magnitudes ranging from Mw 6.2 to Mw 6.97, according to Equation (1) proposed by Wells and Coppersmith (1994). Furthermore, when the faults delineated from seismic profiles are evaluated together with bathymetric data, three fault segments located between the Sinop Basin and the Mid-Black Sea Ridge, with lengths of approximately 10 km and 20 km, are interpreted to have the potential to generate earthquakes with magnitudes of Mw 6.2 and Mw 6.58. Considering that the seismogenic threshold is generally accepted as Mw ≥ 6.0 (McCalpin, 2009), these faults are therefore classified as potentially hazardous. 5. Discussion 5 .1 Bathymetric interpretations and Structural Control of the Sinop Basin Based on bathymetric data, a second submarine channel located in the Yeşilırmak canyon and extending in the NNE-SSW direction is identified. (Fig. 4). This channel heads south towards the mouth of the Kızılırmak River delta. Accordingly, this channel is interpreted as a paleochannel of the Kızılırmak River, indicating that the active bed of the river shifted towards the NW over time. The tributaries of the Yeşilırmak River, which reaches the sea along the Bafra coast, have been observed to have eroded, and the seafloor morphology has been significantly disrupted in certain seismic lines (Fig. 8 and 9). Significant deformation has also been observed in the Pliocene-Quaternary units beneath the seafloor in these areas. Four main seismic units ranging from the Upper Cretaceous – Paleocene to the Plio-Quaternary present are identified in the seismic lines. The acoustic basement unit (U4), defined as Upper Cretaceous-Paleocene, is generally cut and/or bounded by inactive faults, which are defined as the third group in our study. (Fig. 8 and 9). This accumulation was interrupted at the end of the Early Eocene by compressional tectonics resulting from the closure of Neotethys (Robinson et al., 1996; Görür et al., 1997). Therefore, the internal structure of unit U4 is wavy, sinuous and sometimes chaotic, and its contact with the overlying units is manifested by a strong reflection. This contact forms an anticline on the Arkhangelsky Ridge and a syncline beneath the Sinop Basin. This fold contact, which corresponds to the main unconformity reflection in seismic lines, is cut by several faults in many places. The U3 Unit which is symbolized by semi-horizontal reflections on the unconformity plane, presents a very thin geometry on the ridge and thickens from the edge to the middle of the basin. This unit may correspond to deposition related to the initial isolation of the Paratethys at the end of the Eocene, and the beginning of the Oligocene is characterized by the Maykop Series, which contains prominent, generally fine-grained organic-rich sediments and sandstone packages. (Simmons et al., 2018). The U3 unit, defined as Eocene unit, overlies the acoustic basement. This unit is thought to have been eroded or transported to other areas within the study area due to erosion/landslides. They are particularly visible on the Arkhangelsky Ridge in Lines 2 and 6, and below both the Arkhangelsky Rridge and Yeşilırmak canyon floors in Lines 10 and 11. The sediment thickness in the Black Sea Ridge is approximately 5–6 km (Nikishin et al. 2003). The Sinop Basin is filled with Pliocene and Quaternary sediments that lie conformably with the basement (Meredith and Egan 2002). Rangin et al. (2002) suggested that the Sinop Basin formed as a side effect of recent movements of the North Anatolian Fault. Meredith and Egan (2002) demonstrated the existence of major extensional faults that form half-graben structures on both flanks of the Black Sea Ridge. Based on the interpretation of high-resolution seismic data, Dondurur and Çifçi (2007) indicated that the tectonic setting upper and middle continental slope of the Central Black Sea is controlled by the Arkhangelsky Ridge. Accordingly, the upper part of the ridge and the upper sediment units were affected by normal faults that formed small-scale graben structures. Dondurur and Çifçi (2007) also suggested that a second uplift formed on the northern mid-slope of the ridge. Maden and Dondurur (2013) reported that positive and negative gravity anomalies lie parallel to each other and are closely related to the tectonic structure of the region. However, according to their studies the normal fault zones surrounding the Arkhangelsky Ridge have been buried due to excessive sedimentation in the Black Sea. According to this definition, none of these fault zones show active faulting reaching to the sea floor, and therefore, earthquakes occurring in these fault zones are very unlikely to cause displacement on the sea floor. However, in this study, in all seismic lines the faults that reach and cut the seafloor in are identified and mapped. The mapped fault systems along the northeastern and southwestern margins of the Sinop basin converge downward and diverge upward, forming a characteristic negative flower structure (Fig. 10). Fig. 12 and 13 show determination of the continuity of active faults identified. Three strike-slip fault zones (sb1-3), parallel to the Sinop coast and parallel to each other, are identified. On the Arkhangelsky Ridge, NW-SE oriented oblique- to strike-slip faults (sb-4-6) that shape the ridge and indirectly affect the Central Black Sea Ridge are also mapped. Among these structures, the fault zone defined as sb6 is determined to extend along the Arkhangelsky Ridge without interruption in all sections perpendicular to the ridge and therefore the fault. However, parallel faults sb4 and sb5 are identified in the sections that cut the Archangeslky Ridge perpendicularly (Line 2, 8 and 9). These structures, as defined in the literature, are a characteristic type of structural deformation observed in the shape of a 'V' due to the effect of blocks developing around the fault plane and collapsing downwards, and are evaluated as negative flower structures. Negative flower structure and reverse fault structures are also mapped in the deep seismic lines off the Cide-Sinop coast in the east of the area (İşcan et al., 2018; 2019). Considering that reverse fault structures are a type of fault formed as a result of the earth's crust moving towards each other under the effect of compression forces and provided by large-scale dynamic processes of the earth, it can be interpreted that this situation occurred due to extension in our study area and compression on the Sinop-Cide side (İşcan et al., 2019). Fig. 14 shows location map of the regional tectonic lineaments. The dark blue strike-slip faults are interpreted in this study. Fault structures have been identified in seismic lines as a result of marine seismic studies and basin modeling conducted in the region (Meredith and Egan 2002; Rangin et al. 2002; Finetti et al. 1988; Cloetingh et al. 2003; Robinson et al. 1995; Robinson et al. 1996; Dondurur and Çifçi 2007). Active tectonic structures, particularly those located along the coasts of Sinop and Samsun provinces, that have not been identified in the existing literature have been observed and mapped as a result of the present study. When we examine the study area on a regional scale, we can see that, in addition to strike-slip faults, reverse faults and normal faults are also active. This indicates that the Sinop basin is deformed within a right-lateral brittle shear zone. In this zone, where the North Anatolian Fault forms the main structure, east-west trending lines cause reverse/thrust faults, while northwest-southeast trending lines cause oblique faults. Accordingly, sigma 1 should be in the northwest-southeast direction, the smallest stress axis (sigma 3) should be in the northeast-southwest direction, and sigma 2 should be close to vertical. The proposed right-lateral shear zone can be tested with multidisciplinary studies. In previous researches, a conceptual model based on the positive flower structure developed in the North Anatolian Fault was presented (Yıldırım et al., 2013). This situation is thought to be due to the presence of a northward-trending thrust system and a negative flower structure associated with the transpressional deformation associated with the NAF. The depth of the Andrusov Ridge was observed as 14 s in the seismic sections in the study by Nikishin et al. (2014). Due to the signal penetration capacity of the seismic source equipment used in the project, the ridge structure could not be observed as depth of the ridge structure is around 4 s. Several earlier studies proposed that faults bordering the Arkhangelsky Ridge and the Sinop Basin are inactive or buried beneath thick sedimentary cover. However, our seismic profiles clearly show that multiple fault segments cut Plio–Quaternary units and locally offset the seafloor. These observations satisfy widely accepted criteria for active faulting, including deformation of young sediments, morphological expression on the seafloor, and spatial association with recent seismicity. The discrepancy with earlier interpretations primarily arises from differences in data resolution and coverage. The present study employs higher-resolution seismic data and integrates bathymetric observations, allowing the detection of subtle but continuous fault-related deformation that was previously unresolved. Consequently, the southern Black Sea margin cannot be regarded as tectonically quiescent, and fault activity must be re-evaluated within a neotectonic framework. 5 .2 Seismicity and Fault–Earthquake Relationships This study documents the geometry and length of active negative flower structures mapped offshore of Bafra and Samsun and evaluates their earthquake generating potential using the empirical relationships of Wells and Coppersmith (1994). The estimated maximum moment magnitudes range between Mw 6.2 and 6.97, indicating the capacity of these structures to generate moderate to large earthquakes. An assessment of historical seismicity together with instrumental earthquake records spanning the period 1900–2025 reveals a pronounced concentration of seismic activity along the southern Black Sea margin (Fig. 2). Numerous earthquakes with magnitudes exceeding M > 3 have been recorded within the study area and its vicinity. Spatial analysis of epicentral distributions highlights distinct seismic clusters associated with the North Anatolian Fault Zone, the Arkhangelsky Ridge within the study area, and the boundary faults of the Sinop Basin (Fig. 2). Historical accounts indicate that a major earthquake affecting the Amasya and Çorum regions in 1598 was followed by tsunami waves impacting the coastal sector between Sinop and Samsun (Altınok and Ersoy, 2000; Altınok et al., 2009; Nikonov, 1997). These waves reportedly propagated up to approximately 1.6 km inland, resulting in the loss of several thousand lives in coastal settlements (Ambraseys and Finkel, 1995). Additional historical sources similarly describe tsunami effects along the Sinop–Samsun coastline following destructive earthquakes in the Amasya–Çorum region, located east of the study area (Altınok and Ersoy, 2000). One of the most significant instrumental-period tsunami events documented in the Black Sea occurred after the Mw ~6.2–6.5 earthquake offshore Bartın on 3 September 1968. In the aftermath of this event, tsunami wave heights of up to ~3 m were reported, with coastal inundation distances ranging between 50 and 100 m (Altınok and Ersoy, 2000). Despite these observations, the potential impacts of this and similar events on the Samsun and Bafra coastlines have not been systematically investigated. Seismic studies conducted in the Sinop Basin and along the Central Black Sea Ridge suggest the presence of active fault systems and inherited structural frameworks capable of generating large-magnitude earthquakes. Recent high-resolution seismic reflection profiles and multibeam bathymetric data provide compelling evidence for the existence of active fault systems characterized by negative and hybrid flower structures offshore of Sinop and Samsun. These structures exhibit complex kinematic behavior, incorporating strike-slip, normal, and reverse components, and thus reflect a superposition of transtensional and transpressional deformation regimes. Comparable fault systems worldwide are known to be capable of generating earthquakes with magnitudes of Mw ≥ 6, underscoring the seismic significance of the identified structures. The 1939 Erzincan–Fatsa earthquake (Mw 8.0) remains one of the most destructive seismic events affecting northern Türkiye, causing approximately 40,000 fatalities and more than 12,000 injuries (Jackson and McKenzie, 1988). This earthquake also triggered a tsunami along the eastern Black Sea coast, resulting in measurable shoreline modifications. At Fatsa, the coastline reportedly retreated by approximately 50 m immediately after the event and subsequently advanced by about 20 m (Eyidoğan et al., 1991). Although the Black Sea coastal region is generally regarded as an area of relatively low seismicity, historical documentation, instrumental records, and recent tectonic analyses collectively demonstrate that the regional earthquake and tsunami hazard cannot be neglected. The spatial distribution of instrumental and historical earthquakes correlates strongly with the mapped active fault segments within and around the Sinop Basin. Earthquake clusters align with the basin-bounding strike-slip faults and with fault splays forming the negative flower structure (Fig. 2d). This spatial correspondence supports a mechanical linkage between observed seafloor faulting and regional seismicity. Although focal mechanism solutions remain limited offshore, available data indicate a combination of strike-slip and compressional components, consistent with the hybrid transtensional–transpressional deformation inferred from seismic interpretation. These findings demonstrate that the Sinop Basin participates actively in the regional strain field associated with the westward motion of the Anatolian Plate and its interaction with the Central Black Sea Ridge. The primary tsunami-generating mechanisms in the Black Sea are associated with offshore fault rupture and secondary processes triggered by strong onshore earthquakes. In addition, submarine mass movements represent a plausible but still debated source of tsunami generation and should be considered in regional hazard assessments, particularly along the southern Black Sea margin. Given the dense population and critical infrastructure concentrated along the Samsun coastal corridor, the potential consequences of future seismic and tsunamigenic events are significant. The active submarine faults identified in this study therefore constitute a credible source for earthquakes with magnitudes exceeding Mw 6 and for associated tsunami hazards in the central Black Sea region. 5 .3 Comparison of the Sinop Basin with similar negative flower structures worldwide The Sinop Basin is defined as a marine pull-apart basin developed between active strike-slip fault segments in the northern part of the Black Sea (Temel, 2015). Owing to its structural characteristics, the basin is comparable to other examples of negative flower structures developed in both continental and marine tectonic settings. In this section, the structural properties of the Sinop Basin are evaluated through a comparative analysis with ten pull-apart basins formed in different terrestrial and marine tectonic environments (Table 1). The Sinop Basin occupies a tectonic setting characterized by NW–SE trending active oblique to strike-slip fault segments and represents the product of a predominantly transtensional deformation regime (Temel, 2015). In this respect, it exhibits strong structural similarities with pull-apart basins developed along major transform fault systems, such as the Salton Trough along the San Andreas Fault (Lachenbruch, 1985), San Diego Bay (Singleton et al., 2021), and the Alpine Fault of New Zealand (Barnes et al., 2001). Likewise, the Çınarcık and Tekirdağ basins in the Sea of Marmara formed along the offshore segments of the North Anatolian Fault (NAF) and similarly reflect extensional deformation within a strike-slip tectonic framework (Carton et al., 2007; Pondard et al., 2007). The Sinop Basin contains an approximately 4 km–thick sedimentary infill (Temel, 2015). This thickness exceeds that of relatively shallow pull-apart basins such as the Salton Trough (~2–3 km; Lachenbruch, 1985) and San Diego Bay (~1–2 km; Singleton et al., 2021), while remaining lower than that of deeper basins including the Dead Sea Basin (~11 km; Smit, 2008), Erzincan Basin (~6–7 km; NOAA, 1939), and the Tekirdağ Basin (~5 km; Pondard et al., 2007). The marine setting of the Sinop Basin, combined with ongoing tectonic activity and deep-water conditions, provides a favorable environment for substantial sediment accumulation. The horizontal width of the Sinop Basin is estimated to range between approximately 10 and 15 km (Temel, 2015), which is comparable to the dimensions of the Kazova Basin (~5–10 km; Şengör et al., 2005), the Tekirdağ Basin (~10–20 km; Pondard et al., 2007), and the Alpine Fault pull-apart basins (~15–25 km; Barnes et al., 2001). This width is interpreted as the result of extensional deformation localized between strike-slip fault segments. An evaluation of seismicity and tectonic activity associated with the basins listed in Table 1 indicates that the Sinop Basin is situated within an active fault zone and possesses the potential to generate earthquakes of up to Mw ~6.6 (Temel, 2015). In this context, it is comparable to basins associated with major seismic events, such as the 1939 Erzincan earthquake (Mw 7.8; NOAA, 1939) and the 1999 İzmit earthquake (Mw 7.4; Pondard et al., 2007), both of which occurred in highly active strike-slip tectonic settings. Similarly, basins developed within the Andaman Sea (Diehl et al., 2013) and the Salton Trough (Lachenbruch, 1985) are located in transform fault zones characterized by elevated seismicity, suggesting a comparable tectonic risk profile to that of the Sinop Basin. The formation of the Sinop Basin is interpreted to have been governed by extensional deformation occurring between strike-slip fault segments, resulting in the development of a negative flower structure geometry (Temel, 2015). In this regard, the basin shares direct structural similarities with documented negative flower structures in the Tekirdağ Basin (Le Pichon et al., 2001), the Salton Trough (Lachenbruch, 1985), the Andaman Sea (Diehl et al., 2013), and the complex fault systems of the Sea of Marmara (Aksu et al., 2000; Armijo et al., 2005). Negative flower structures form as a consequence of extensional stress within strike-slip fault systems, where fault splays diverge upward, typically producing a pull-apart basin geometry (Sylvester, 1988; Bozkurt, 2001). Table 1 The table summarizes and compares the key structural, morphological, and seismotectonic characteristics of terrestrial and marine pull-apart basins formed in different tectonic settings. Feature Lut Lake Basin (Terrestrial) Erzincan Basin (Terrestrial) Kazova Basin (Terrestrial) Salton Trough (Terrestrial) Andaman Sea Basin (Marine) Alpine Fault –New Zealand (Marine) San Diego Bay Pull-Apart/USA (Marine) Çınarcık Basin (Marine) Tekirdağ Basin (Marine) This Study (Sinop Basin) Tectonic Setting Transtensional pull-apart basin on the left-lateral Dead Sea Fault (Garfunkel, 1996) Strike-slip and extensional segment on the North Anatolian Fault (NAF) (NOAA, 1939) Releasing bend on the Almus segment of the NAF (Şengör et al., 2005) Pull-apart basin on the San Andreas Fault Zone (Lachenbruch, 1985) Back-arc setting, submarine strike-slip basins (Diehl et al., 2013) Submarine releasing segment on a transform fault zone (Barnes et al., 2001) Pull-apart basin in a transform system linked to San Andreas (Singleton et al., 2021) Submarine releasing structure on the NAF segment in the Marmara Sea (Carton et al., 2007) Extensional segment under the Marmara Sea along the NAF (Pondard et al., 2007) Basin bounded by NW-SE active faults (Temel, 2015) Depth / Vertical Dimension ~11 km of sediment, ~8 km sedimentary fill (Smit, 2008) ~6–7 km sedimentary fill (NOAA, 1939) ~3–5 km sedimentary fill (Şengör et al., 2005) ~2–3 km deep (Lachenbruch, 1985 Thick sediment accumulation under seafloor (Diehl et al., 2013) ~5–6 km sedimentary fill (Barnes et al., 2001) Shallow basin with ~1–2 km sedimentary fill (Singleton et al., 2021) ~1200 m water + several km sediment (Carton et al., 2007) ~1000+ m water, ~4–5 km sediment (Pondard et al., 2007) ~4 km sediment fill (Temel, 2015) Width / Horizontal Dimension ~15–20 km wide, ~100 km long (Smit, 2008) ~10 km wide, ~30 km long (NOAA, 1939) ~5–10 km wide (NOAA, 1939) ~10–15 km wide (Crowell et al., 2013) ~10–20 km wide (Diehl et al., 2013) ~15–25 km wide Barnes et al., 2001) ~5–10 km wide (Singleton et al., 2021) ~10–20 km wide ~10–20 km wide (Pondard et al., 2007) ~10–15 km wide (Temel, 2015) Seismicity Moderate to large earthquakes (Garfunkel, 1996) 1939 Erzincan Mw 7.8 earthquake (NOAA, 1939) Moderate-scale earthquakes Şengör et al., (2005) M6+ earthquakes on active segments (Lachenbruch, 1985) High seismicity, tsunami risk (Diehl et al., 2013) Mw 7+ earthquakes; submarine surface ruptures (Howarth et al., 2018) Mw ~6 earthquakes with surface ruptures (USGS, 2021) 1999 Mw 7.4 earthquake and aftershocks Aftershocks along active fault segments (Pondard et al., 2007) Active faults, potential for M6.6 earthquakes (Temel, 2015) Formation Mechanism Releasing bend with normal faults on a left-lateral fault; block subsidence (Smit, 2008) Extension and sedimentation through step-over on strike-slip fault (NOAA, 1939) Graben structure at releasing bend (Şengör et al., 2005) Extension and sedimentation in a transform fault zone (Lachenbruch, 1985) Strike-slip related back-arc rifting and extension (Morley, 2015) Releasing bend morphology; negative flower structure on the seafloor (Barnes et al., 2001) Pull-apart mechanism, graben-type depressions (Maloney, 2019) Submarine releasing bend normal faults (Carton et al., 2007) Sediment accumulation between extensional fault branches (Le Pichon et al., 2001) Opening between active strike-slip faults (Temel, 2015) Such structures play a fundamental role in the development of major sedimentary basins, both in terms of their morphological expression and their capacity to accommodate thick sedimentary successions (Özel Füzün, 2024; Turko, 2024). The structural characteristics of the Sinop Basin closely resemble other well-documented negative flower structures developed along major strike-slip systems worldwide, including basins in the Sea of Marmara, the Dead Sea Transform, the Salton Trough, and the Andaman Sea. Similarities in basin geometry, sediment thickness, fault architecture, and seismic behavior indicate that the Sinop Basin represents a marine analogue of classic pull-apart basins formed in transtensional environments. This comparison places the Sinop Basin within a broader geodynamic context and underscores its relevance as a natural laboratory for studying strike-slip–related basin development in submarine settings. The results discussed above demonstrate that the Sinop Basin is not a passive sedimentary depression but an actively deforming tectonic system shaped by oblique to strike-slip–dominated deformation. The integration of seismic stratigraphy, fault geometry, seafloor morphology, and seismicity provides a consistent framework in which basin evolution, present-day deformation, and seismic hazard are directly linked. These findings form the basis for the conclusions presented below. 6. Conclusions The integration of high-resolution multichannel seismic reflection profiles and multibeam bathymetric data reveals that the Sinop Basin is an actively deforming tectonic depression governed by the offshore extension of the North Anatolian Fault Zone. Stratigraphic analysis identifies four distinct seismic units ranging from the Eocene to the Plio-Quaternary, which have been shaped by a complex interplay of strike-slip and extensional tectonics. Interpretation of multibeam bathymetric data and multichannel high resolution seismic reflection profiles acquired in the offshore Sinop study area allowed the identification of four principal seismic units. Four main seismic units, ranging from Eocene to Plio-Quaternary, were identified and correlated across the basin. The lowermost unit is interpreted as the acoustic basement, whereas the overlying units are dated from the Eocene to the Plio–Quaternary. Throughout this stratigraphic interval observed in the seismic sections, multiple deformation phases associated with active faulting have resulted in the development of uplifted ridges and anticline structures around the basin margins. Although extensional structures are dominant, well-developed anticlines affecting even the youngest sedimentary units—particularly within the U1 seismic unit in the southwestern sector—record localized compressional deformation indicative of a local transpressional regime. These folds are interpreted to have formed either prior to or contemporaneously with transtensional deformation. Accordingly, while the overall bathymetric expression of the basin is characterized by a pull-apart depression morphology, the structural architecture indicates that it should also be considered a negative flower structure. Bathymetric and seismic data demonstrate that the basin has developed a complex submarine morphology controlled by active tectonic deformation associated with the offshore continuation of the North Anatolian Fault Zone. The steeply dipping strike-slip fault zones bounding the basin along its northeastern and southwestern margins merge at depth and splay upward, forming a palm-shaped geometry characteristic of negative flower structures (Fig. 15). Figure 15 shows 3D block model of the study area showing batymetric, stratigraphic and structural features of Sinop basin. This structural configuration indicates that the basin evolved under a predominantly transtensional tectonic regime, in which strike-slip motion and extensional deformation acted simultaneously, consistent with development within releasing bends of a major strike-slip fault system. Seismic sections show that the marine study area is intensely deformed by active faulting. Three distinct fault types have been identified in the region, and the active fault groups were systematically traced and mapped in detail on the seismic profiles. Among these, reverse faults constitute the second group of active faults. These reverse faults are identified by the upward displacement of reflectors on one side of the fault relative to the other. Based on this geometry, the affected branch is interpreted as a probable former (paleo-) channel. This observation suggests a progressive northwestward migration of the active channel of the Kızılırmak River over time. Such migration is interpreted as evidence of westward tilting of the region occurring contemporaneously with fault-related uplift driven by active tectonism. The Sinop Basin exhibits strong structural similarities with other basins hosting negative flower structures developed in both continental and marine environments, in terms of its tectonic setting, sediment thickness, fault geometry, and seismic potential (Table 1). In particular, comparisons with the Tekirdağ, Çınarcık, Salton, and Andaman basins indicate that the formation mechanism and morphology of the Sinop Basin display the characteristic features of strike-slip–related pull-apart systems. Accordingly, the Sinop Basin represents a valuable natural laboratory for investigating the geodynamic evolution of pull-apart basins developed within active fault zones. Slip surfaces identified in the regional seismic data clearly indicate the presence of mechanically weak layers along which mass movement has occurred. The slip surface observed in the northern sector of the Arkhangelsky Ridge, in particular, suggests that mass movements in this area were dominated by lateral sliding mechanisms. This observation confirms the complex nature of deformation and the presence of structurally controlled weak zones within the basin. The continuity of these slip surfaces provides important constraints for identifying mechanically weak domains and for assessing the potential risk of submarine landslides or large-scale mass movement processes. Overall, this study challenges previous interpretations that regarded the southern Black Sea margin as tectonically quiescent. Instead, it demonstrates that the Sinop Basin represents an active component of the regional neotectonic framework and should be incorporated into future seismic and coastal hazard assessments. The Sinop Basin thus provides a key example of strike-slip–related basin development in a submarine setting and contributes to a broader understanding of deformation processes along continental margins. Collectively this study provides the first integrated geophysical evidence that the Sinop Basin is located in actively deforming strike-slip system with significant seismic hazard implications for the southern Black Sea margin. By reconciling the dominant transtensional geometry (negative flower structure) with localized compressional features (transpression), this aligns well with modern structural interpretations of evolving strike-slip basins. The inclusion of the Kızılırmak paleo-channel migration serves as compelling independent evidence, effectively linking deep-seated structural deformation (tilting and uplift) to surface geomorphological processes. Furthermore, placing the basin in the context of major global analogues, such as the Sea of Marmara and Salton Trough, validates the proposed kinematic model and substantiates the challenge to the region's historical interpretation as tectonically quiescent. Declarations Financing Statement This study is financially supported by 7th European Marie-Curie ITN 607996 no. Anatolian pLateau climatE and Tectonic Hazards (ALErT) Project. Conflict of Interest Statement The authors declare that they have no conflict of interest. Author Contribution S.Ö. , G.Ç., H.S. ,S.O. wrote the main manuscript text Ö.B. prepared figuresÖ.C prepared figuresC.E. prepared figuresÖ.Ö. and O.A. data collection1-9 All authors reviewed the manuscript Acknowledgements This study constitutes part of the PhD thesis of Sevinç Özel Füzün. The multichannel seismic and multibeam bathmetry data presented in this article were collected within the framework of the 7th European Marie-Curie ITN Anatolian pLateau climatE and Tectonic Hazards (ALErT) Project. Data processing was carried out using the facilities of the Marine Geophysics Laboratory (SeisLab), affiliated with the Institute of Marine Sciences and Technology, Dokuz Eylül University. We are deeply indebted to the State Planning Organization (DPT) for their invaluable support in procuring equipment and establishing the data acquisition, processing and interpretation SeisLab through project 2003K120360. Furthermore, we would like to express our profound appreciation to SEAMAP company for their technical support regarding the laboratory instrumentation utilized during marine data acquisition campaigns. Also, we would like to thank Europe Commission, European Marine Observation and Data Network (EMODnet Geology) for their excellent cooperation. Data Availability The authors do not have permission to share data. References Ajala R, Persaud P, Stock JM, Fuis GS, Hole JA, Goldman M, Scheirer D (2019) Three-dimensional basin and fault structure from a detailed seismic velocity model of Coachella Valley, Southern California. J Geophys Res Solid Earth 124(5):4728–4750. https://doi.org/10.1029/2018JB016260 Aksoy E, İnceöz M, Koçyiğit A (2007) Lake Hazar Basin: a negative flower structure on the East Anatolian Fault System (EAFS), SE Türkiye. Turk J Earth Sci 16(3):319–338 Algan O, Gökaşan E, Gazioğlu ZY, Yücel B, Alpar B, Güneysu C, Kırcı E, Demirel S, Sarı E, Ongan D (2002) A high-resolution seismic study in Sakarya Delta and Submarine Canyon, southern Black Sea shelf. Cont Shelf Res 22(10):1511–1527. https://doi.org/10.1016/S0278-4343(02)00012-2 Altınok Y, Alpar B, Özer N, Ünlü S, Meriç E, Nazik A, Avşar N, Balkıs N, Aykurt H, Taş S (2009) Black Sea tsunamis and paleotsunami studies on the Thrace Coasts of Turkey. In: Proceedings of MEDCOAST 2009 International Conference , Sochi, Russia, 10–14 November 2009, pp 931–942 Altınok Y, Ersoy Ş (2000) Tsunamis observed on and near the Turkish coast. Nat Hazards 21:185–205. https://doi.org/10.1023/A:1008130512498 Ambraseys NN, Finkel CA (1995) The seismicity of Turkey and adjacent areas: a historical review: 1500–1800 . Eren Yayıncılık, İstanbul Armijo R, Pondard N, Meyer B, Uçarkuş G, de Lépinay BM, Malavieille J, Dominguez S, Gustcher MA, Schmidt S, Beck C et al (2005) Submarine fault scarps in the Sea of Marmara pull-apart (North Anatolian Fault): implications for seismic hazard in Istanbul. Geochem Geophys Geosyst 6(6):Q06009. https://doi.org/10.1029/2004GC000896 Barka AA, Kadinsky-Cade K (1988) Strike-slip fault geometry in Türkiye and its influence on earthquake activity. Tectonics 7(3):663–684. https://doi.org/10.1029/TC007i003p00663 Ben-Avraham Z, Ten Brink US (1989) Transverse faults and segmentation of strike-slip faults: examples from the Dead Sea Transform. Tectonophysics 180:37–47. https://doi.org/10.1016/0040-1951(90)90370-N Bozkurt E, Koçyiğit A (1996) The Kazova basin: an active negative flower structure on the Almus Fault Zone, a splay fault system of the North Anatolian Fault Zone, Türkiye. Tectonophysics 265(1–2):239–254. https://doi.org/10.1016/S0040-1951(96)00045-5 Brothers DS, Harding AJ, Babcock JM (2009) Tectonic evolution of the Salton Sea inferred from seismic reflection data. Nat Geosci 2(8):581–584. https://doi.org/10.1038/ngeo590 Christie-Blick N, Biddle KT (1985) Deformation and basin formation along strike-slip faults. In: Biddle KT, Christie-Blick N (eds) Strike-slip deformation, basin formation, and sedimentation . SEPM Special Publication 37, pp 1–34 Curray JR (2005) Tectonics and history of the Andaman Sea region. J Asian Earth Sci 25(1):187–232. https://doi.org/10.1016/j.jseaes.2004.09.001 Dondurur D, Çifçi G (2007) Acoustic structure and recent sediment transport processes on the continental slope of Yeşilırmak River fan, Eastern Black Sea. Mar Geol 237(1–2):37–53. https://doi.org/10.1016/j.margeo.2006.10.035 Dondurur D, Çifçi G (2007) Acoustic evidence of shallow gas and gas hydrates in the Black Sea sediments off the coast of Samsun. Geo-Marine Letters 27:311–320. https://doi.org/10.1007/s00367-007-0084-9 Dondurur D, Küçük HM, Çifçi G (2013) Quaternary mass wasting on the western Black Sea margin, offshore of Amasra. Glob Planet Change 103:248–260. https://doi.org/10.1016/j.gloplacha.2012.05.009 Elmas A, Karslı H (2021) Tectonic and crustal structure of Arkhangelsky ridge using Bouguer gravity data. Mar Geophys Res 42:21. https://doi.org/10.1007/s11001-021-09443-z Fialko Y (2006) Interseismic strain accumulation and the earthquake potential on the southern San Andreas fault system. Nature 441(7096):968–971. https://doi.org/10.1038/nature04797 Finetti I, Bricchi G, Ben AD, Pipan M, Xuan Z (1988) Geophysical study of the Black Sea. Boll Geofis Teor Appl 30(117):197–324 Garfunkel Z, Ben-Avraham Z (1996) The structure of the Dead Sea basin. Tectonophysics 266(1–4):155–176. https://doi.org/10.1016/S0040-1951(96)00188-6 Gartman A, Hein JR (2019) Mineralization at oceanic transform faults and fracture zones. In: Duarte JC (ed) Transform Plate Boundaries and Fracture Zones . Elsevier, pp 105–118. https://doi.org/10.1016/B978-0-12-812064-4.00005-0 Görür N (1988) Timing of opening of the Black Sea basin. Tectonophysics 147(3–4):247–262. https://doi.org/10.1016/0040-1951(88)90189-8 Görür N, Monod O, Okay AI, Şengör AMC, Tüysüz O, Yiğitbaş E, Sakınç M, Akkök R (1997) Palaeogeographic and tectonic position of the Carboniferous rocks of the Western Pontides (Türkiye) in the frame of the Variscan belt. Bull Soc Géol Fr 168(2):197–205 Graham R, Kaymakci N, Horn B (2013) Revealing the mysteries of the Black Sea. GEO ExPro 10(5):58–63 Harding TP (1985) Seismic characteristics and identification of negative flower structures, positive flower structures, and positive structural inversion. AAPG Bull 69(4):582–600. https://doi.org/10.1306/AD462538-16F7-11D7-8645000102C1865D Harris PT, Macmillan-Lawler M, Rupp J, Baker EK (2014) Geomorphology of the oceans. Mar Geol 352:4–24. https://doi.org/10.1016/j.margeo.2014.01.011 Haşimoğlu BY, Çifçi G, Lacassin R, Fernández-Blanco D, Özel Ö (2016) Tectonics of the Kızılırmak delta and Sinop Basin offshore Pontides, evidence from new high-resolution seismic and bathymetric data. Paper presented at the AGU Fall Meeting 2016 , San Francisco, USA, 12–16 December 2016 Huang Q, Liu Y (2017) Hybrid flower structures in strike-slip fault systems: insights from sandbox modeling. Tectonophysics 721:237–251. https://doi.org/10.1016/j.tecto.2017.10.017 Hubert A, Garcia D, Moernaut J, Van Daele M, Damci E, Cagatay N, De Batist M (2008) The Hazar pull-apart along the East Anatolian Fault: structure and active deformation. Paper presented at the Tectonic Studies Group Annual Meeting , La Roche-en-Ardenne, Belgium, 8–10 January 2008 Jipa DC, Panin N (2020) Narrow shelf canyons vs. wide shelf canyons: two distinct types of Black Sea submarine canyons. Quat Int 540:120–136. https://doi.org/10.1016/j.quaint.2018.08.006 Jipa DC, Panin N, Olariu C, Pop C (2020) Black Sea submarine valleys—patterns, systems, networks. Geo-Eco-Marina 26:15–40. https://doi.org/10.5281/zenodo.4682752 Kalafat D (2017) Seismicity and tectonics of the Black Sea. Int J Earth Sci Geophys 3(11):1–8. https://doi.org/10.35840/2631-5033/1811 Kalafat D, Güneş Y, Kara M, Deniz P, Kekovalı K, Kuleli HS, Gülen L, Yılmazer M, Özel NM (2007) A revised and extended earthquake catalogue for Türkiye since 1900 (M ≥ 4.0) . Boğaziçi University, Kandilli Observatory and Earthquake Research Institute, İstanbul (Report) Kennedy MP, Clarke SH (1999) Analysis of late Quaternary faulting in San Diego Bay and hazard implications for the San Diego region, California. Bull Seismol Soc Am 89(6):1465–1477 Le Pichon X, Chamot-Rooke N, Lallemant S (2001) The Western Mediterranean Basin. J Geophys Res Solid Earth 106(B8):16119–16130. https://doi.org/10.1029/2000JB900403 Lericolais G, Popescu I, Guichard F, Popescu SM (2011) Assessment of Black Sea water-level fluctuations since the Last Glacial Maximum based on seismic and core data. Marine Geology 284:1–16. https://doi.org/10.1016/j.margeo.2011.03.003 Letouzey J, Biju-Duval B, Dorkel A, Gonnard R, Krischev K, Montadert L, Sungurlu O (1977) The Black Sea: a marginal basin—geophysical and geological data. In: Biju-Duval B, Montadert L (eds) Structural History of the Mediterranean Basins . Editions Technip, Paris, pp 363–376 Maden N, Öztürk S (2015) Seismic b-values, Bouguer gravity and heat flow data beneath Eastern Anatolia, Türkiye: tectonic implications. Surv Geophys 36:549–570. https://doi.org/10.1007/s10712-015-9327-1 Maloney JM, Driscoll NW, Kent G, Duke S, Freeman T, Bormann JM (2016) Segmentation and step-overs along strike-slip fault systems in the inner California borderlands: implications for fault architecture and basin formation. In: Applied Geology in California , Environmental Engineering Geologists 26, pp 655–677 McCalpin JP (2009) Paleoseismology , 2nd edn. Academic Press Mechie J, Abu-Ayyash K, Ben-Avraham Z, El-Kelani R, Qabbani I, Weber M, DESIRE Group (2009) Crustal structure of the southern Dead Sea basin derived from project DESIRE wide-angle seismic data. Geophys J Int 178(1):457–478. https://doi.org/10.1111/j.1365-246X.2009.04161.x Meisner LB, Tugolesov DA (2003) Basic reflections from sedimentary filling of Black Sea depression (correlation and stratigraphic tying). Stratigr Geol Correl 11(6):595–608 Meredith DJ, Egan SS (2002) The geological and geodynamic evolution of the Eastern Black Sea Basin: insights from 2-D and 3-D tectonic modelling. Tectonophysics 350(2):157–179. https://doi.org/10.1016/S0040-1951(02)00121-X Munteanu I, Matenco L, Dinu C, Cloetingh S (2011) Kinematics of back-arc inversion of the Western Black Sea basin. Tectonics 30(5):TC5004. https://doi.org/10.1029/2011TC002865 Nikonov A (1997) Tsunami—A threat from the south? Search and Development, Science in Russia 6:13–19 Nikishin AM, Okay AI, Tüysüz O, Demirer A, Wannier M, Amelin N, Petrov E (2015) The Black Sea basins structure and history: new model based on new deep penetration regional seismic data. Part 2: tectonic history and palaeogeography. Mar Pet Geol 59:656–670. https://doi.org/10.1016/j.marpetgeo.2014.08.018 Oaie G, Seghedi A, Rădulescu V (2016) Natural marine hazards in the Black Sea and the system of their monitoring and real-time warning. Geo-Eco-Marina 22:5–28. https://doi.org/10.5281/zenodo.889593 Ocakoğlu N, İşcan Y, Gül FK (2022) Mapping onland river channels up to the seafloor along offshore Cide-Sinop in the Southern Black Sea from the perspective of the Black Sea flooding. Int J Environ Geoinformatics 9(1):116–126. https://doi.org/10.30897/ijegeo.948042 Ocakoğlu N, İşcan Y, Kılıç Y, Özel O (2018) Morphologic and seismic evidence of rapid submergence offshore Cide-Sinop in the southern Black Sea shelf. Geomorphology 311:76–89. https://doi.org/10.1016/j.geomorph.2018.03.008 Okay AI, Şengör AMC, Görür N (1994) Kinematic history of the opening of the Black Sea and its effect on the surrounding regions. Geology 22(3):267–270. https://doi.org/10.1130/0091-7613(1994)0222.3.CO;2 Özel Füzün, S. (2024l). Investigation Of Mid-Black Sea Ridge/Sinop trough with marine geophysical methods . PhD Thesis, (Publication No. 905319) Dokuz Eylül University The Graduate School of Natural and Applied Sciences , İzmir, Türkiye. Özel Füzün S, Çifçi G, Sözbilir H, Okay Günaydın S, Atgın O, Özel Ö (2024) Stratigraphic and structural features of the Sinop Basin close to the Mid Black Sea Ridge using multi-channel seismic and multibeam bathymetric data. Recep Tayyip Erdoğan University Journal of Science and Engineering 5:49–59. https://doi.org/10.53501/rteufemud.1469379 Panin N, Ion E, Ion G (1997) Black Sea GIS (CD-ROM). GEF Black Sea Environmental Programme Panin N, Jipa D (2002) Danube River sediment input and its interaction with the North-western Black Sea. Estuar Coast Shelf Sci 54(3):551–562. https://doi.org/10.1006/ecss.2000.0664 Pondard N, Armijo R, King GCP, Meyer B, Flerit F (2007) Fault interactions in the Sea of Marmara pull-apart (North Anatolian Fault): earthquake clustering and propagating earthquake sequences. Geophys J Int 171(3):1185–1197. https://doi.org/10.1111/j.1365-246X.2007.03580.x Popescu I (2002) Analyse des processus sédimentaires récents dans l'éventail profond du Danube (mer noire) [Analysis of recent sedimentary processes in the Danube deep-sea fan (Black Sea)]. PhD thesis, Université de Bretagne Occidentale, Brest, France & University of Bucharest, Bucharest, Romania, 282 pp. Available at: http://www.theses.fr/2002BRES2012 Popescu I (2008) Processus sédimentaires récents dans l’éventail profond du Danube (Mer Noire) [Recent sedimentary processes in the Danube deep-sea fan (Black Sea)]. Geo-Eco-Marina 15(Special Publication 2):202 pp Popescu I, Lericolais G, Panin N, Normand A, Dinu C, Le Drezen E (2004) The Danube submarine canyon (Black Sea): morphology and sedimentary processes. Mar Geol 206:249–265. https://doi.org/10.1016/j.margeo.2004.03.003 Popescu I, Panin N, Jipa D, Lericolais G, Ion G (2015) Submarine canyons of the Black Sea basin. In: Briand F (ed) Submarine Canyons of the Mediterranean Sea and the Black Sea , CIESM Monograph 47, Monaco, pp 143–152. Racano S, Schildgen T, Ballato P, Yıldırım C, Wittmann H (2023) Rock-uplift history of the Central Pontides from river-profile inversions and implications for development of the North Anatolian Fault. Earth Planet Sci Lett 616:118231. https://doi.org/10.1016/j.epsl.2023.118231 Rangin C, Bader AG, Pascal G, Ecevitoğlu B, Görür N (2002) Deep structure of the Mid Black Sea High (offshore Türkiye) imaged by multi-channel seismic survey (BLACKSIS cruise). Mar Geol 182(3–4):265–278. https://doi.org/10.1016/S0025-3227(01)00236-5 Robinson AG, Banks CJ, Rutherford MM, Hirst JPP (1995) Stratigraphic and structural development of the Eastern Pontides, Türkiye. J Geol Soc London 152(5):861–872. https://doi.org/10.1144/gsjgs.152.5.0861 Robinson AG, Kerusov E (1997) Regional and petroleum geology of the Black Sea and surrounding region . American Association of Petroleum Geologists Robinson AG, Rudat JH, Banks CJ, Wiles RLF (1996) Petroleum geology of the Black Sea. Mar Pet Geol 13(2):195–223. https://doi.org/10.1016/0264-8172(95)00042-9 Ross DA, Uchupi E, Prada KE, MacIlvaine JC (1974) Bathymetry and microphotography of Black Sea. American Association of Petroleum Geologists Salcher BC, Meurers B, Decker K, Hölzel M, Wagreich M (2012) Strike-slip tectonics and Quaternary basin formation along the Vienna Basin fault system inferred from Bouguer gravity derivatives. Tectonics 31(3):TC3005. https://doi.org/10.1029/2011TC002979 Schleder Z, Krezsek C, Turi V, Tari G, Kosi W, Fallah M (2015) Regional structure of the Western Black Sea Basin: constraints from cross-section balancing. In: Post PJ, Coleman JJ et al (eds) Petroleum systems in “Rift” basins . GCSSEPM Foundation, pp 396–411. https://doi.org/10.5724/gcs.15.34.0396 Seeber L, Armbruster JG (2000) Earthquakes and asperities in the transition fault of the Marmara Sea: possible source of the next great earthquake. Seismol Res Lett 71(3):374–388. https://doi.org/10.1785/gssrl.71.3.374 Simmons MD, Tari GC, Okay AI (2018) Petroleum geology of the Black Sea: introduction. Geol Soc London Spec Publ 464:1–18. https://doi.org/10.1144/SP464.16 Singh SC, Moeremans R (2017) Anatomy of the Andaman–Nicobar subduction system from seismic reflection data. Geol Soc London Mem 47(1):193–204. https://doi.org/10.1144/M47.13 Singleton DM, Maloney JM, Brothers DS, Klotsko S, Driscoll NW, Rockwell TK (2021) Pull-apart basin, fault structure, marine paleoseismology, marine geophysics in the Newport-Inglewood–Rose Canyon fault system, inner California continental borderland, San Diego Bay. Front Earth Sci 9:641346. https://doi.org/10.3389/feart.2021.641346 Sipahioğlu NO, Karahanoğlu N, Altıner D (2013) Analysis of Plio-Quaternary deep marine systems and their evolution in a compressional tectonic regime, Eastern Black Sea Basin. Mar Pet Geol 43:187–207. https://doi.org/10.1016/j.marpetgeo.2013.02.008 Smit J, Brun JP, Cloetingh S, Ben-Avraham Z (2008) Pull-apart basin formation and development in narrow transform zones with application to the Dead Sea Basin. Tectonics 27(6):TC6018. https://doi.org/10.1029/2007TC002119 Softa M, Emre T, Sözbilir H, Spencer JQ, Turan M (2018) Geomorphic evidence for active tectonic deformation in the coastal part of Eastern Black Sea, Eastern Pontides, Türkiye. Geodin Acta 30(1):249–264. https://doi.org/10.1080/09853111.2018.1494776 Softa M, Spencer JQ, Sözbilir H, Huot S, Emre T (2021) Luminescence dating of Quaternary marine terraces from the coastal part of Eastern Black Sea and their tectonic implications for the Eastern Pontides, Türkiye. Turk J Earth Sci 30(3):359–378. https://doi.org/10.3906/yer-2005-21 Somoza L, Medialdea T, Terrinha P, Ramos A, Vázquez JT (2021) Submarine active faults and morphotectonics around the Iberian margins: seismic and tsunami hazards. Front Earth Sci 9:653639. https://doi.org/10.3389/feart.2021.653639 Sylvester AG (1988) Strike-slip faults. Geol Soc Am Bull 100(11):1666–1703. https://doi.org/10.1130/0016-7606(1988)1002.3.CO;2 Tari G, Fallah M, Kosi W, Schleder Z, Turi V, Krezsek C (2015) Regional rift structure of the Western Black Sea Basin: map-view kinematics. Paper presented at the 34th Annual GCSSEPM Foundation Perkins-Rosen Research Conference , Houston, USA, 13–16 December 2015 Tari GC, Simmons MD (2018) History of deepwater exploration in the Black Sea and an overview of deepwater petroleum play types. Geol Soc London Spec Publ 464:439–475. https://doi.org/10.1144/SP464.16 Thierry S, Dick S, George S, Benoit L, Cyrille P (2019) EMODnet bathymetry: a compilation of bathymetric data in the European waters. Paper presented at OCEANS 2019 , Marseille, France, 17–20 June 2019 Tugolesov DA, Gorshkov AS, Meysner LB, Soloviov VV, Khakhalev EM, Akilova YuV, Akentieva GP, Gabidulina TI, Kolomeytseva SA, Kochneva TYu, Pereturina IG, Plashihina IN (1985) Tectonics of the Mesozoic sediments of the Black Sea Basin . Nedra, Moscow (in Russian), 215 pp Turko M (2024) Strike-slip kinematics for pop-ups and pull-aparts. GeoExPro Magazine . https://geoexpro.com/strike-slip-kinematics-for-pop-ups-and-pull-aparts/. Accessed 10 Sep 2024 U.S. Geological Survey (2014) SRTM 1 Arc-Second Global (30 m) [Digital Elevation Model]. U.S. Geological Survey. https://earthexplorer.usgs.gov Wei EA, Holmes JJ, Driscoll NW (2020) Strike-slip transpressional uplift offshore San Onofre, California inhibits sediment delivery to the deep sea. Front Earth Sci 8:51. https://doi.org/10.3389/feart.2020.00051 Wells DL, Coppersmith KJ (1994) New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bull Seismol Soc Am 84(4):974–1002 Yaltırak C, Alpar B, Yüce H (2002) Tectonic elements controlling the evolution of the Gulf of Saros, NE Aegean Sea, Türkiye. Mar Geol 190(1–2):261–282. https://doi.org/10.1016/S0025-3227(02)00350-4 Yıldırım C, Schildgen TF, Echtler H, Melnick D, Strecker MR (2011) Late Neogene and active orogenic uplift in the Central Pontides associated with the North Anatolian Fault: implications for the northern margin of the Central Anatolian Plateau, Türkiye. Tectonics 30(5):TC5005. https://doi.org/10.1029/2010TC002756 Yıldırım C, Schildgen TF, Echtler H, Melnick D, Strecker MR et al (2013) Tectonic implications of fluvial incision and pediment deformation at the northern margin of the Central Anatolian Plateau based on multiple cosmogenic nuclides. Tectonics 32:1107–1120. https://doi.org/10.1002/tect.20066 Zonenshain LP, Le Pichon X (1986) Deep basins of the Black Sea and Caspian Sea as remnants of Mesozoic back-arc basins. Tectonophysics 123(1–4):181–211. https://doi.org/10.1016/0040-1951(86)90197-6 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-8779310","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":588892158,"identity":"3e59a6a4-01aa-4452-abfe-70b15cb108f8","order_by":0,"name":"Dr. SEVİNÇ ÖZEL FÜZÜN","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIie3RIQvCQBTA8TcWLDesz7J9hROjgl/FIWgxCJaFBWVwK/sABsHPYDfceLB0H2Bi0bK0oNjFsYHN26Lh/uWu/HiPOwCT6U+TzWHvbqy+zDoTK+JfIrsNswR2Il6cDGkdguvFOxGUAUG/t+L28/ybcKU47TMYWUkqLgdFMEhKDrLQEFzMyNmCH6Evro4g4PmqIprNvGPREOHdxcZ5E0zbCOS2rEmClrCdbTUFWwhXc0kswxEyPxocsiVDVayl0i0Wp9GLhZPqxSh9lOHY7cfz0y3QLdaE31v9Ne3AZDKZTNo+J19TGRkA5LAAAAAASUVORK5CYII=","orcid":"","institution":"Dokuz Eylul University, Institute of Marine Sciences and Technology, 35340 İzmir, Türkiye","correspondingAuthor":true,"prefix":"Dr.","firstName":"SEVİNÇ","middleName":"ÖZEL","lastName":"FÜZÜN","suffix":""},{"id":588892159,"identity":"01cc0c9f-72b1-4d5d-9196-a5bd516775d3","order_by":1,"name":"Prof. Dr. GÜNAY Çifci","email":"","orcid":"","institution":"Dokuz Eylul University, Institute of Marine Sciences and Technology, 35340 İzmir, Türkiye","correspondingAuthor":false,"prefix":"","firstName":"Prof.","middleName":"Dr. GÜNAY","lastName":"Çifci","suffix":""},{"id":588892160,"identity":"9cfc5a11-5753-4bfe-be47-d2b34aaa1aa0","order_by":2,"name":"Prof. Dr. HASAN Sözbillir","email":"","orcid":"","institution":"Earthquake Research and Application Center, Dokuz Eylül University","correspondingAuthor":false,"prefix":"","firstName":"Prof.","middleName":"Dr. HASAN","lastName":"Sözbillir","suffix":""},{"id":588892161,"identity":"71e69716-d13f-469f-9a71-4cbaf9af97f4","order_by":3,"name":"Associate.Prof. Seda Okay Günaydın","email":"","orcid":"","institution":"Dokuz Eylul University, Institute of Marine Sciences and Technology, 35340 İzmir, Türkiye","correspondingAuthor":false,"prefix":"","firstName":"Associate.Prof.","middleName":"Seda Okay","lastName":"Günaydın","suffix":""},{"id":588892162,"identity":"100d5d20-62e1-474a-9361-3d86fc51e015","order_by":4,"name":"Dr. Özkan Özel","email":"","orcid":"","institution":"Dokuz Eylul University, Institute of Marine Sciences and Technology, 35340 İzmir, Türkiye","correspondingAuthor":false,"prefix":"Dr. Ö","firstName":"zkan","middleName":"","lastName":"Özel","suffix":""},{"id":588892163,"identity":"92cc8547-d358-4697-8666-d3e51af3dd94","order_by":5,"name":"Dr. Orhan Atgın","email":"","orcid":"","institution":"Dokuz Eylul University, Institute of Marine Sciences and Technology, 35340 İzmir, Türkiye","correspondingAuthor":false,"prefix":"Dr.","firstName":"Orhan","middleName":"","lastName":"Atgın","suffix":""},{"id":588892164,"identity":"8052866e-2e1a-4e5a-aa2e-b2d10953fb2e","order_by":6,"name":"Dr. Özde Bakak","email":"","orcid":"","institution":"Dokuz Eylul University, Institute of Marine Sciences and Technology, 35340 İzmir, Türkiye","correspondingAuthor":false,"prefix":"Dr. Ö","firstName":"zde","middleName":"","lastName":"Bakak","suffix":""},{"id":588892165,"identity":"39e3c841-5402-482e-8c65-c49c5b634fec","order_by":7,"name":"Dr. Özkan Cevdet Özdağ","email":"","orcid":"","institution":"Department of Geophysics Engineering, Faculty of Engineering","correspondingAuthor":false,"prefix":"Dr. Ö","firstName":"zkan","middleName":"Cevdet","lastName":"Özdağ","suffix":""},{"id":588892166,"identity":"ef7ea3fe-279c-4a19-984d-753ddb1467bb","order_by":8,"name":"Can Eytemiz","email":"","orcid":"","institution":"Dokuz Eylul University, Institute of Marine Sciences and Technology, 35340 İzmir, Türkiye","correspondingAuthor":false,"prefix":"","firstName":"Can","middleName":"","lastName":"Eytemiz","suffix":""}],"badges":[],"createdAt":"2026-02-03 18:53:44","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8779310/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8779310/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102388061,"identity":"cdddc004-d99f-4b3c-a401-399449622a76","added_by":"auto","created_at":"2026-02-11 08:19:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1716817,"visible":true,"origin":"","legend":"\u003cp\u003eLocation map of the study area (Modified from Robinson et al., 1996 and Oaie et al., 2016). a) Main tectonic elements of Türkiye (modified from Finetti et al., 1988; Robinson et al., 1995; Kazmin et al., 2000; Hippolyte et al., 2018). Abbreviations: ArR – Arkhangelsky Ridge, AnR – Andrusov Ridge, SR – Shatsky Ridge, Ttr – Tuapse Trough, WSB – Western Black Sea, EBS – Eastern Black Sea, NAF – North Anatolian Fault, EAF – Eastern Anatolian Fault, DSF – Dead Sea Fault. Topographic and bathymetric data were obtained from the SRTM Worldwide Elevation Online Data/Global Mapper and NOAA - GEBCO 2022 free online bathymetric database (U.S. Geological Survey, 2014), b) Location of the Sinop Trough, major tectonic lineaments, and ridge structures, c) Locations of multi-channel seismic profiles overlaid on the multibeam bathymetric map.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/feb5c832f220c83d9cf565ff.png"},{"id":102388065,"identity":"83769277-c49d-4ea0-971e-f4ef1c589d9a","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2472706,"visible":true,"origin":"","legend":"\u003cp\u003eDifferent distribution maps for earthquake epicenter points in focused area and the coastal zone of Black Sea, a) the spatial distribution of historical earthquakes catalogue through the coastal zone, b) the instrumental earthquakes catalogue (Mw \u0026gt; 4) through the coastal zone, c) the spatial distribution of historical earthquakes catalogue in the focused area and its surroundings, d) the instrumental earthquakes catalogue (Mw \u0026gt; 4) of focused area, and e) earthquake point located only in the sea and the focal mechanism solutions (AFAD Catalogue). The instrumental earthquake data were obtained from the Disaster and Emergency Management Authority (AFAD – in Turkey) website Earthquake Catalog, covering the period from 01/01/1900 to 01/01/2025. The tectonic structures shown were taken from Hippolyte et al. (2018).\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/334411e59f77f655ba496f70.png"},{"id":102398249,"identity":"3dbbbf77-2b21-4f99-93a2-c53042a2113f","added_by":"auto","created_at":"2026-02-11 10:21:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":317091,"visible":true,"origin":"","legend":"\u003cp\u003e3D block model of earthquakes (M \u0026gt; 1, depth \u0026lt; 40 km) in the study area between May 1900 and May 2025. Seismicity is mainly concentrated along the North Anatolian Fault zone, with sparse activity in offshore areas of the Black Sea. The map was created using QGIS with the UTM Zone 36N projection and WGS84 datum. The geodetic parameters employed were the Universal Transverse Mercator (UTM) Zone 36N projection and the World Geodetic System 1984 (WGS84) datum.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/7863576cbdf94c6ca1c2436f.png"},{"id":102388063,"identity":"dc9ff024-1550-454c-8264-f859e35c6acf","added_by":"auto","created_at":"2026-02-11 08:19:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1614994,"visible":true,"origin":"","legend":"\u003cp\u003ea) The bathymetry map of project area obtained using the ELAC-SeaBeam 1050D system. and b)\u003cstrong\u003e \u003c/strong\u003eThe map illustrates the bathymetric and morphotectonic features of the Sinop Basin. Multibeam bathymetric data reveal the presence of a secondary paleo-channel aligned in a NE–SW direction, which connects to the Yeşilırmak submarine canyon. It is suggested that this channel may have once been fed by the Kızılırmak River. Dashed black lines on the map represent active faults, some of which reach to the seafloor, forming morphologically distinct fault scarps.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/f8aaf60017c246177d17053c.png"},{"id":102398262,"identity":"c54826c2-ae4f-4adf-8f1e-6aa687c1d437","added_by":"auto","created_at":"2026-02-11 10:21:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":339798,"visible":true,"origin":"","legend":"\u003cp\u003eThe morphological structures of the study area are investigated through (a) a schematic illustration of a typical continental margin cross-section, (b) NE–SW oriented profiles are selected for the analysis of seafloor morphology, and (c–e) are depth–slope variations along these profiles. Distinct morphological units such as the continental shelf, canyon/channel systems, the Arkhangelsky Ridge, and the abyssal plain are clearly observable. These morphological features provide valuable insights into the seafloor evolution and sedimentary accumulation processes. The Arkhangelsky Ridge forms a prominent morphological high, beyond which the abyssal plain begins.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/a47b705722d3146167a60a86.png"},{"id":102388071,"identity":"52109690-ab13-414b-a0d0-0240d951016e","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2590381,"visible":true,"origin":"","legend":"\u003cp\u003eNE-SW-oriented Line2 seismic reflection section and morphological structures, a) NW-SE direction sb1 active fault segment located in the shallow region of Sinop Through, b) NW-SE directional sb2 active fault segment, c) sliding material and sliding surface, d) the head scarp, also called the scarp at the upper edge of a landslide or the main scarp, and the material that slides from here is defined as sliding material, e) active negative flower structure and f) the mode of active negative flower and g) the active fault group defined as sb6, a strike-slip fault observerd toward the termination point east of the Arkhangelsky Ridge.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/04861394a0a1667625f27a88.png"},{"id":102398226,"identity":"4f4e251e-3a5e-40fd-adaa-3384c53299e0","added_by":"auto","created_at":"2026-02-11 10:21:50","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2270788,"visible":true,"origin":"","legend":"\u003cp\u003eSeismic reflection section (NE-SW-oriented Line6). On Line 6, one of the cross-sections perpendicular to the Mid-Black Sea Ridge, it is similarly observed that some faults do not reach the seabed.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/3feb7ac01824bf613bafb6ce.png"},{"id":102388075,"identity":"f328560f-bd2d-4393-840f-66c7c419ace5","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":2050700,"visible":true,"origin":"","legend":"\u003cp\u003eSeismic reflection section profile (SW-NE Line10) showing interpreted and uninterested versions. Line 10, extending perpendicular to the Mid Black Sea Ridge in a NE-SW direction, shows the stratigraphic and structural features of the Sinop basin. Faults are observed cross-cutting the Plio-Quaternary unit and the seafloor. The seismic profile reveals three principal stratigraphic successions: an upper Plio-Quaternary unit (U1), a middle Oligo-Miocene unit (U2), and a lower Eocene unit (U3). Beneath these units lies an acoustic basement characterized by weak and chaotic reflections. Within the U1 (Plio-Quaternary) unit, the observed channel structures are interpreted as sedimentary deposits from submarine current systems that developed during the late Quaternary period. Regarding the U2 (Oligo-Miocene) unit, the local thickness changes are inferred to have resulted from differential subsidence or block movements associated with faulting throughout the depositional history.\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/d6f3a757b91a827caf134248.png"},{"id":102398493,"identity":"3bb5a4ed-82ec-450d-a9fa-ee8df3478535","added_by":"auto","created_at":"2026-02-11 10:23:03","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1493635,"visible":true,"origin":"","legend":"\u003cp\u003eSeismic reflection sections showing interpreted and uninterpreted versions of Line 11 showing interpreted and uninterpreted versions of Line 11. This line, extending perpendicular to the Central Black Sea Ridge in a SW-NE direction, shows the stratigraphic and structural features of the Sinop basin. Faults that reach the surface and cross-cut the seafloor represent tectonic structures that may still be active. These faults deform the Plio-Quaternary unit, thereby controlling modern sedimentation patterns. Notable changes in the fault structure are observed at the transition between the Oligo-Miocene and Eocene units. The acoustic basement (U4) is identified as the zone with weak/chaotic reflections beginning after 2.5–3.5 seconds (s) TWT (Two-Way Travel Time). This basement is interpreted as the oldest stratigraphic unit, composed of Cenozoic (Paleocene or older) rocks.\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/15a056d744e118f998b74d0a.png"},{"id":102397930,"identity":"977ba3fb-4b09-4dc4-92a1-c70208967084","added_by":"auto","created_at":"2026-02-11 10:20:11","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1592733,"visible":true,"origin":"","legend":"\u003cp\u003ea-b) The interpreted sections of seismic Lines 8 and 9, c) the locations of \u003cu\u003eprofiles on\u003c/u\u003e bathymetry map. In these sections, a fault system identified as SB5 exhibits characteristics of a negative flower structure. This tectonic feature, located particularly along the Arkhangelsky Ridge, is known to influence the extensional regime within the Central Black Sea Ridge and the study area.\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/30dd78d949d4a75c03fd8ce5.png"},{"id":102388076,"identity":"397de809-5f0d-4340-8e89-a7f3c58a30e7","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":833163,"visible":true,"origin":"","legend":"\u003cp\u003eNW-SE oriented seismic line parallel to the coastline Line17. The seismic section illustrates the configuration of a transfer ramp developed at a step-over of NW-SE trending faults. In our coast-parallel section, we observe the ridge. Furthermore, in our coast-parallel sections running along the ridge, we can state that the fault bounding the Sinop Basin to the south is an en-echelon fault. It can also be stated that at step-overs within certain segments of this fault, faults corresponding to (or forming) a transfer ramp have developed.\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/0a90779fa4e5c175002b2b54.png"},{"id":102388073,"identity":"7fdbad69-cae6-44d3-bf83-3b6136e93469","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":2925776,"visible":true,"origin":"","legend":"\u003cp\u003eDetermination of the continuity of active faults identified in Line 2 – Line 6 from seismic sections. Fault definitions are defined as “sb” since the study area is located within the Sinop Basin.\u003c/p\u003e","description":"","filename":"image12.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/2d7acbb22e8597982b46ffe2.png"},{"id":102388067,"identity":"f9109008-2969-4c24-bf8e-f2b72be3fc13","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":2884929,"visible":true,"origin":"","legend":"\u003cp\u003eDetermination of the continuity of active faults identified in Line 8 – Line 11 from seismic sections. Fault definitions are defined as “sb” since the study area is located within the Sinop Basin.\u003c/p\u003e","description":"","filename":"image13.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/ee8a4e7a821346eb2ca9529b.png"},{"id":102388069,"identity":"1094c754-8663-4b24-a325-32291946c74a","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":1425015,"visible":true,"origin":"","legend":"\u003cp\u003eLocation map of the regional tectonic lineaments. The dark blue strike-slip faults are interpreted in a resulting of this paper. The offshore fault lines (shown in black) are simplified from İşcan et al. (2019), Ocakoğlu et al. (2018) and Kalafat (2017). The onshore faults are compiled from Yıldırım et al. (2011) and \u003cbr\u003e\nAbbreviations: \u003cstrong\u003eBF\u003c/strong\u003e – Balıfakı Fault; \u003cstrong\u003eEF\u003c/strong\u003e – Erikli Fault.\u003c/p\u003e","description":"","filename":"image14.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/548139efe3fba1842699d3d1.png"},{"id":102388074,"identity":"57903e26-02c1-4a0e-8d85-141bd3d4043c","added_by":"auto","created_at":"2026-02-11 08:19:11","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":2373620,"visible":true,"origin":"","legend":"\u003cp\u003ea) 3D block model of the study area showing batymetric, stratigraphic and structural features of Sinop basin, b) a syntethic cross section showing a pair of negative and positive flower structures across the Sinop basin.\u003c/p\u003e","description":"","filename":"image15.png","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/6b19f9e7ed7a959b18d77f3e.png"},{"id":102962114,"identity":"f5cd0cb7-98e4-43ef-94f1-7c31c97cf87a","added_by":"auto","created_at":"2026-02-19 04:02:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":27148229,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8779310/v1/ff9bb30c-e57d-4f8a-a0f4-9b2ff24f53bb.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Tectonic and Morphological Features of a Submarine Negative Flower Structure: In the Sinop Basin (Central Black Sea) and the Evaluation of Regional Seismic Hazard ","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eTurkey is one of the most tectonically active regions on Earth, experiencing intense deformation as a result of the interaction between the Eurasian, Anatolian, Arabian, and African plates. The westward movement of the Anatolian Plate along the right-lateral North Anatolian Fault (NAF) and the left-lateral East Anatolian Fault (EAF), together with ongoing subduction and collision processes along the southern and northern margins of the country, control both terrestrial and marine tectonics (Kalafat, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Softa et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe geological structure of the Black Sea has been under investigation since the publications of regional seismic lines for the entire area in the 1980's (Tugolesov et al.,1985; Finetti et al.,1988; Belousov et al., 1988, 1989). More recent seismic lines were shot in parts of the Black Sea and were published by Robinson et al. (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e1996\u003c/span\u003e), Dinu et al. (2005), Afanasenkov et al. (2007), Shillington et al. (2008), Rangin et al. (\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), Khriachtchevskaia et al. (2009, 2010), Munteanu et al. (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), Menlikli et al. (2009), Stovba et al. (2009), Tari et al. (2009), Stuart et al. (2011), Nikishin et al. (2010, 2012), Mityukov et al. (2012), Almendinger et al. (2011), Georgiev (2012), TPAO/BP Eastern Black Sea Project Study Group (1997), Gozhik et al. (2010), Graham et al. (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In recent years, various petroleum companies have acquired a very large amount of 2D and 3D seismic data for individual blocks, though results of these operations are not published.\u003c/p\u003e \u003cp\u003eAs observed in the seismic lines presented in the study by Nikishin et al. (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), the Andrusov Ridge clearly has a sedimentary cover of Cretaceous\u0026ndash;Cenozoic age and also contains volcanic rocks from the Cretaceous period. In contrast, the seismic data over the Arkhangelsky Ridge do not indicate the presence of a thick Mesozoic cover. Within this framework, the Sinop Basin stands out as an important structural and seismotectonic feature, although its origin remains debated. Some researchers interpret the basin as a forearc basin formed by crustal flexure (Meredith and Egan, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), while others propose a transtensional graben model (Rangin et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). The Arkhangelsky Ridge, located north of the Sinop Basin and bordered by normal fault zones, is currently buried due to excessive sedimentation in the Black Sea (Dondurur and \u0026Ccedil;if\u0026ccedil;i, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The researcher argued that none of these fault zones exhibit active faulting that reaches the seafloor, and therefore, the likelihood of earthquakes causing any displacement of the seafloor in these zones is considered very low. Especially, the neotectonic structures of the Black Sea coasts are not as active compared to other regions (İşcan et al., 2019). Additionally, the weak and sparse seismicity observed in the region defined as secondary neotectonic (Şeng\u0026ouml;r, 1980) has not been associated with the main tectonic movements of Anatolia up to the present. The areas between the Black Sea coasts-particularly the tectonic lineaments forming the Central Black Sea Ridge-and the North Anatolian Fault Zone (NAFZ) have long been considered inactive (İşcan et al., 2019).\u003c/p\u003e \u003cp\u003eOn the other hand, our detailed observations from seismic sections and previous studies indicate that some of these faults do, in fact, cut through to the seafloor and cause significant strike- to dip-slip displacements (Kalafat, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003ez\u0026uuml;n-\u0026Ouml;zel, 2024). It has been suggested that the basement of the two east-west oriented basins formed and influenced by the Arkhangelsky Ridge on the Central Black Sea High consists of thinned continental crust and/or oceanic crust (Belousov, 1988; Finetti et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Yegorova et al., 2010; Yegorova et al., 2013; Graham et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). However, it is considered necessary to clarify whether this ridge continues to be shaped by active or inactive faults.\u003c/p\u003e \u003cp\u003eThe aim of this study,\u003c/p\u003e \u003cp\u003e(1) detect the morphological features of focused area,\u003c/p\u003e \u003cp\u003e(1) define the stratigraphic and structural framework of the basin,\u003c/p\u003e \u003cp\u003e(2) classify and map faults located between Bafra (Samsun) offshore and the Central Black Sea Ridge,\u003c/p\u003e \u003cp\u003e(3) reveal and regionally assess the submarine negative flower structure,\u003c/p\u003e \u003cp\u003e(4) recalculate the potential earthquake magnitudes based on the length-magnitude relationships of the tectonic lineaments revealed in cross-sections, using the mathematical relations proposed by Wells and Coppersmith (\u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e1994\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis study was carried out within the framework of the AlerT project (Anatolian Climate and Tectonic Hazards; Project Code: 607996) project. The ALeRT project was designed to investigate the uplift history of the Anatolian Plate, basin development, and the controlling tectonic mechanisms governing these processes. The project was conducted through a consortium comprising 11 academic institutions and 5 private companies, focusing primarily on onshore tectonic and climatic interactions across Anatolia. The marine component of the project in T\u0026uuml;rkiye was undertaken by Dokuz Eyl\u0026uuml;l University, Institute of Marine Sciences and Technology, providing offshore geophysical data essential for integrating marine and terrestrial tectonic frameworks. In addition to its scientific objectives, ALeRT was structured as an Initial Training Network (ITN), aiming to enhance the research capacity of early-stage researchers by offering advanced training opportunities, fostering integration into established research teams, and supporting long-term academic and professional career development.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Regional Geology and Seismotectonic Setting","content":"\u003cp\u003eThe study area is located along the coast of Samsun, at the point where the Kızılırmak River meets the Black Sea, encompassing a significant portion of the Arkhangelsky Ridge, which extends across the central Black Sea (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). To the south of the region, along the Sinop coast of Turkey, lies the Kızılırmak River, while the Yeşilırmak River is situated to the east. These two major rivers play a critical role in shaping the hydrological and geomorphological structure of the region. According to Popescu et al. (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), the effects of the Kızılırmak and Yeşilırmak rivers on the seafloor are observed in bathymetric data as large submarine canyons. The branches of the Yeşilırmak submarine valley system extend over 100 km, and its drainage basin covers an area of approximately 3,600 km\u0026sup2; (Jipa et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This system exhibits a dendritic structure, resembling vein-like patterns, particularly in areas with gentler slopes (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). In their deep seismic studies, Dondurur and \u0026Ccedil;if\u0026ccedil;i (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) successfully mapped the submarine canyons of the Yeşilırmak system in detail, reporting a total length exceeding 120 km, of which approximately 60 km display a dendritic pattern. The Black Sea basin was shaped by an extensional tectonic regime during the Early Cretaceous and transitioned into a compressional regime due to the collision between the Eurasian and Arabian plates in the Early Eocene (Robinson et al., \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Spadini et al., 1996; Tari et al., 2000). Following this transition, regions along the Black Sea coast, such as the Pontides, the Caucasus to the east, Crimea to the north, and the Balkans to the west, were incorporated into a compressional tectonic system. The Eastern Black Sea Basin (EBSB), bounded by the Arkhangelsky Ridge, and the Western Black Sea Basin (WBSB) differ significantly in terms of their formation processes, tectonic orientations, and sedimentary thicknesses (Robinson et al., \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Shillington et al., 2008; Nikishin et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Deep seismic data reveal that sedimentary sequences up to 12\u0026ndash;14 km thick have accumulated in the basin from the Late Cretaceous to the present (Nikishin et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Finetti et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). In the deepest parts of the basin, oceanic crust lies at approximately 10 km below thick sedimentary layers, whereas the coastal and ridge regions are composed of continental crust (Sosson et al., 2010; Anatoly et al., 2015; Yegrova et al., 2010). Multichannel seismic reflection-refraction, gravity, and magnetic data from the region reveal that the eastern and western basins both with oceanic crust exhibit distinct structural characteristics (Rangin et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Dinu et al., 2005) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Geological and geophysical evidence including offshore seismic reflection profiles (Finetti et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1988\u003c/span\u003e), coastal morphology (Meisner et al., 1995), onshore geology and morphology (Okay and Şahint\u0026uuml;rk, 1997), and recent seismic activity (Neprochnov and Ross, 1978) indicate that the compressional tectonic regime in the eastern Black Sea region remains active. In contrast, there is no significant evidence of compressional or extensional regimes in the southwestern Black Sea region. The ridge in the central Black Sea represents a zone of thinned continental crust, forming the northwestern boundary of the EBSB. This basin is underlain by oceanic crust and is covered by sediment layers less than 12 km thick. Unlike the western Black Sea, the ridges and basins in the eastern part are intersected by numerous faults (Finetti et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). These two sub-basins are separated by the Central Black Sea Ridge, bounded by the northwest\u0026ndash;southeast trending Andrussov Ridge in the north and the Arkhangelsky Ridge in the south (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). This ridge functioned as a structural barrier until the Oligocene\u0026ndash;Early Miocene, after which it became a single depositional center, buried under younger sediments (Kazmin et al., 2000; Nikishin et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Two major seismic belts influence the study area. The first is the North Anatolian Fault Zone (NAFZ), a prominent right-lateral strike-slip fault located near the coast (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). The second involves the first seismological evidence of an active thrust structure along the southern coast. Focal mechanism solutions indicate the coexistence of thrusting and strike-slip faulting in the region (Kalafat, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Between 2006 and 2015, moment tensor (CMT) solutions were obtained for earthquakes with M\u0026thinsp;\u0026gt;\u0026thinsp;3.7 using broadband station data (Alptekin et al., 1985; HRV, 1977\u0026ndash;2013; Kalafat, 1998). These solutions were computed using regional broadband velocity waveform data (Dreger, 2002; Sokos and Zahradnik, 2013). Only events recorded by at least four digital broadband seismic stations were analyzed. For events between 1968 and 2006, global datasets or published solutions were used. The focal mechanisms of events with M\u0026thinsp;\u0026gt;\u0026thinsp;3.7 predominantly indicate north\u0026ndash;south compression with a minor east\u0026ndash;west component.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. Material and Method","content":"\u003cp\u003eTo investigate the fault architecture and stratigraphic framework of the Sinop Basin, high-resolution multichannel seismic and multibeam bathymetric data were utilized. These datasets were collected during a marine survey aboard the R/V Koca Piri Reis, operated by the Institute of Marine Sciences and Technology at Dokuz Eyl\u0026uuml;l University in 2015. The survey performed in the frame of the ALERT (Anatolian Plateau Climate and Tectonic Hazards) Project, funded by the European Union\u0026rsquo;s 7th Framework Programme (Project Code: 607996), which aimed to evaluate tectonic and climatic hazards across the broader Anatolian region.\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Seismic Data Acquisition and Processing\u003c/h2\u003e \u003cp\u003eAs the sole marine partner in the ALERT Project, Dokuz Eyl\u0026uuml;l University acquired approximately 1300 km of multichannel seismic reflection, CHIRP sub-bottom profiling (which resolves shallow stratigraphy at high resolution), and multibeam bathymetric data (used to map seafloor morphology). The survey was conducted along a total of 17 lines 13 oriented NW\u0026ndash;SE and 4 NE\u0026ndash;SW using the R/V K. Piri Reis research vessel (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). A 216 channel seismic recorder with a 1350 m digital streamer was used for the acquisition. The seismic source consisted of a GI gun with a volume of 45\u0026thinsp;+\u0026thinsp;105 inc\u0026sup3;. Shot spacing was 25 m, with a sampling rate of 1 ms and a record length of 6000 ms. The data were processed at the Marine Geophysics SeisLab laboratory using Landmark Graphics ProMAX software and analyzed with Seismic Micro Tech\u0026rsquo;s Kingdom Suite software.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Bathymetry Data\u003c/h2\u003e \u003cp\u003eMultibeam bathymetry data were collected using the ELAC-SeaBeam 1050D system, with 50Hz transdusers, mounted on the hull of the R/V Piri Reis research vessel, belonging to Dokuz Eyl\u0026uuml;l University\u0026rsquo;s Institute of Marine Sciences and Technology. The DM505 sensor, which detects and immediately corrects the vessel\u0026rsquo;s movement in all three dimensions during data collection, was also used. Echosounder system is designed to collect data in both deep and shallow waters and features 126 beams with a total scanning width of 153\u0026deg; when all beams are utilized. The instrument operates with a beam angle of 1.5 \u0026times; 1.5˚ and the footprint varies between 13 and 40m. The collected data were also processed and edited using the Caraibes program and gridded with 100-m cell size for this area (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Seismicity\u003c/h2\u003e \u003cp\u003eThe study area and the earthquake epicenter locations along the Black Sea coastal zone were mapped in two separate groups: historical earthquakes and instrumental-period earthquakes. All earthquake records were obtained from the Historical and Instrumental Earthquake Catalog available on the official website of the Disaster and Emergency Management Authority (AFAD). The spatial distribution density of historical earthquakes was classified based on intensity (I) into different categories, namely I\u0026thinsp;\u0026lt;\u0026thinsp;6 and 6\u0026thinsp;\u0026lt;\u0026thinsp;I\u0026thinsp;\u0026lt;\u0026thinsp;12. The instrumental earthquake dataset includes events with moment magnitude Mw\u0026thinsp;\u0026gt;\u0026thinsp;4 that occurred between 01 January 1900 and 01 January 2025 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Earthquake maps were generated using the Geographic Information System (GIS)-based ArcGIS 10.8 software. To investigate the relationship between earthquake depth and seismicity, a 3D block model was constructed using earthquake data with magnitudes Mw\u0026thinsp;\u0026gt;\u0026thinsp;1 and focal depths shallower than 40 km (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The model was generated using QGIS software. The geodetic parameters adopted for the study area are the Universal Transverse Mercator (UTM) projection, Zone 36N, and the World Geodetic System 1984 (WGS84) datum.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3\u003c/b\u003e\u003cb\u003e.4 Potential Earthquake Magnitude Calculation\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eFormulations for estimating maximum earthquake magnitudes on fault segments have been derived based on empirical relationships between magnitude, rupture length, rupture width, rupture area, and surface displacement (Emre et al., 2016). In assessing the seismic potential of active tectonic structures in the study area, empirical relationships based on surface rupture length are among the commonly used methods. Four different formulas have been proposed for estimating the potential for possible earthquake generation: Utsu and Seki (1954), Wells and Coppersmith (\u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e1994\u003c/span\u003e), Ellsworth (2003), and Christophersen and Smith (2000). However, considering the surface rupture and fault types present in the region, the formulation developed by Wells and Coppersmith (\u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e1994\u003c/span\u003e), which covers all fault types, was selected as the most appropriate and is presented below:\u003c/p\u003e \u003cp\u003eM\u0026thinsp;=\u0026thinsp;4.86\u0026thinsp;+\u0026thinsp;1.32 x log(SRL) (1)\u003c/p\u003e \u003cp\u003ein the Eq.\u0026nbsp;(1), M and SRL represents the moment magnitude (Mw) and denotes the surface rupture length (in kilometers), respectively. This relationship was developed and applied based on surface rupture data from numerous historical and instrumental earthquakes, covering normal, reverse, and strike-slip fault types (REF). Due to its empirical nature, the maximum moment magnitude that a tectonic structure with a known fault length can produce can be estimated through this formulation.\u003c/p\u003e \u003cp\u003eSuch estimates are of great importance for seismic hazard analyses, engineering geology studies, and the development of earthquake scenarios (Bonilla et al., 1984; Ulusoy et al., 2004; Wesnousky, 2008; Irsyam et al., 2020; Cremen and Galasso, 2020; G\u0026uuml;rboğa et al., 2024). However, it should be noted that this relationship is empirical and relies solely on surface rupture length, independent of the geometric and kinematic characteristics of the fault. Therefore, it is recommended to evaluate its applicability in different tectonic regimes before use.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results","content":"\u003cp\u003e\u003cem\u003e4\u003c/em\u003e\u003cem\u003e.1 B\u003c/em\u003e\u003cem\u003eathymetry Map\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAccording to bathymetry data, the water depth within the study area is between 50 and 2000 m. The shelf break lies at approximately 200 m, while the Arkhangelsky Ridge is located at a depth of approximately 300 m. After the Arkhangelsky Ridge, it joins the deepest part of the Black Sea, which has an almost ideally flat bottom. On the onshore part of the study area, it is observed that the deep valleys of the Kızılırmak and Yeşilırmak rivers were formed on the shores of Sinop and Bafra, respectively. At the same time, it is observed that these rivers flow into both the central Black Sea ridge and the Sinop Graben and become a single channel towards the NW. In addition, a total of four submarine channels are identified within the study area, which merge to form a larger and wider U-shaped channel. The study also revealed the existence of a second submarine channel, trending NNE-SSW, connected to the Yeşilırmak submarine canyon. This channel extends northeastward, starting from the Kızılırmak River delta, and joins the Yeşilırmak channel. Bathymetric data also indicate that the Yeşilırmak submarine channel is the axial submarine canyon of the Sinop Basin, trending northwest.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn Fig. \u0026nbsp;5, continental margin structures are evaluated based on the depth\u0026ndash;slope graphs of Profiles 1\u0026ndash;3 (Fig. \u0026nbsp; 5a). Accordingly, Profile 1, located at the termination of the Arkhangelsky Ridge in the northern part of the study area, exhibits a relatively wide continental shelf, followed by the development of canyon/channel systems beyond the shelf break (Fig. \u0026nbsp;5b). In Profiles 1 and 3, the canyon structures appear to be more prominent, indicating enhanced erosional activity and sediment transport pathways along these sectors of the continental slope break (Fig. \u0026nbsp;5c-e).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTwo distinct submarine channel systems fed by the Yeşilırmak River are clearly identifiable on the seafloor based on multibeam bathymetric data (\u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024). These channels display markedly different along-axis continuities, with the main channel extending for more than 120 km and a secondary channel reaching approximately 40 km in length, consistent with previous regional observations (Dondurur and \u0026Ccedil;if\u0026ccedil;i 2007; \u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024).\u003c/p\u003e\n\u003cp\u003eThe secondary channel, which branches from the Yeşilırmak canyon and trends toward the mouth of the Kızılırmak River delta, has been identified through detailed morphometric analysis of multibeam bathymetric data and is interpreted as representing a paleochannel associated with the former course of the Kızılırmak River (\u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024). The high sediment load supplied by the Yeşilırmak River facilitates the development and sustained activity of deep-sea fan systems, allowing the main channel to function as a major sediment transport pathway extending toward the central Black Sea basin (Dondurur and \u0026Ccedil;if\u0026ccedil;i 2007; Jipa et al. 2020). In addition, a third submarine feature characterized by a well-developed canyon morphology and related to the Kızılırmak River extends for approximately 44 km and is interpreted as a paleochannel based on its geomorphic configuration and stratigraphic context (Algan et al. 2002; \u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024). These submarine channel and canyon systems become prominent approximately 15\u0026ndash;20 km offshore of the Samsun coastline, coinciding with the transition from the continental shelf to the continental slope, where slope gradients increase and erosional processes intensify (Popescu et al. 2015; \u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024).\u003c/p\u003e\n\u003cp\u003eThe evolution and activity of these channel systems are strongly influenced by the stratified hydrodynamic structure of the Black Sea, characterized by low-salinity surface waters overlying denser, anoxic deep waters (Jipa et al. 2020).During the Late Pleistocene (W\u0026uuml;rm glacial stage), a relative sea-level fall of approximately 120\u0026ndash;150 m caused major rivers to discharge directly onto the continental slope, promoting canyon incision and enhanced downslope sediment transport (Lericolais et al. 2011).Sediment distribution within the canyons has been controlled by a combination of bottom-current activity, slope instability, and episodic turbidity currents, resulting in a complex internal sedimentary architecture (Dondurur and \u0026Ccedil;if\u0026ccedil;i 2007).The canyon floors are dominated by sandy to coarse-grained deposits associated with high-energy turbidity flows, whereas canyon walls and inter-canyon ridges are characterized by fine-grained, organic-rich hemipelagic sediments and locally developed sapropel layers (Dondurur and \u0026Ccedil;if\u0026ccedil;i 2007; Jipa et al. 2020).High-resolution seismic data further reveal the presence of shallow gas accumulations and gas-hydrate indicators within the sedimentary succession, particularly along canyon flanks and levee-like features (Dondurur and \u0026Ccedil;if\u0026ccedil;i 2007).\u003c/p\u003e\n\u003cp\u003eThe maximum water depth of the submarine canyon system reaches approximately 1450 m, while the Yeşilırmak-related channel networks are traceable within a depth range of 850\u0026ndash;1700 m (\u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024).\u003c/p\u003e\n\u003cp\u003eSubmarine extensions of both the Yeşilırmak and Kızılırmak river systems originate near the shelf edge and continue downslope between 850 and 1450 m water depths, merging at approximately 1450 m and extending basinward toward the basin plain, where their morphological influence gradually diminishes (Popescu et al. 2015; \u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024).Paleochannel segments have been rapidly infilled by fine-grained sediments during Holocene sea-level rise, producing chaotic to discontinuous seismic facies and locally developed graded bedding observed in high-resolution seismic profiles (Algan et al. 2002; \u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024).\u003c/p\u003e\n\u003cp\u003eTable 1\u003cstrong\u003e.\u003c/strong\u003e Morphometric characteristics of submarine channel systems related to the Yeşilırmak and Kızılırmak Rivers in the central Black Sea (based on multibeam bathymetric map, Fig. 3). Length and depth values are derived from the bathymetric data and supporting literature. The Yeşilırmak system is larger and more dendritic, while the Kızılırmak system is slightly smaller but of comparable depth extent. All values are cited from this study (\u0026Ouml;zel F\u0026uuml;z\u0026uuml;n et al. 2024) and previous works (e.g. Dondurur \u0026amp; \u0026Ccedil;if\u0026ccedil;i 2007; Algan et al. 2002; Jipa \u0026amp; Panin 2020).\u003c/p\u003e\n\u003cp\u003eBoth canyon systems incise the continental shelf and extend from near the river delta mouths (tens of meters water depth) to the base of the continental slope (approximately 1.8\u0026ndash;2.0 km deep) in the Sinop Basin. The Yeşilırmak canyon network has an overall length exceeding 120 km with extensive dendritic tributaries, whereas the Kızılırmak canyon is slightly shorter (over 90 km) and joins the Yeşilırmak system mid-slope. (Measurements based on Fig. 3 and data from \u0026Ouml;zel F\u0026uuml;z\u0026uuml;n \u003cem\u003eet al.\u003c/em\u003e 2024).\u003c/p\u003e\n\u003cp\u003eMultibeam bathymetric data acquired from the Sinop Basin reveal the presence of a secondary, NE\u0026ndash;SW trending paleo-channel that is morphologically linked to the Yeşilırmak submarine canyon. This configuration suggests that the modern canyon-channel system may not represent a stable, long-term sediment transport pattern, but rather records a reorganization of fluvial-to-marine sediment pathways across the continental shelf.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.2 Seismic Units and Faults\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe seismic sections in project area were conducted along a total of 17 lines 13 oriented NW\u0026ndash;SE and 4 NE\u0026ndash;SW \u0026nbsp;(Fig. \u0026nbsp;1c). In total, 1300km seismic profiles were interpreted and evaluated; however, the interpretations presented in this study focus on seismic lines with 2, 6, 8, 9, 10 and 11.\u0026nbsp;During the stratigraphic interpretation of the seismic sections from the study area, four distinct seismic units were identified based on the structural characteristics of the region, seismic velocity data from the Central Black Sea Ridge (Finetti et al., 1988), and recent literature (İşcan et al., 2019). The oldest seismic unit is associated with the acoustic basement (U4). This unit generally exhibits undulating reflections that are subparallel to the seafloor. Overlying this, Unit U3 covers the U4 unit; however, its lateral continuity could not be fully traced across the region due to erosion or mass-wasting processes. Unit U3 has been interpreted as Eocene-aged strata. The overlying Unit U2, which blankets the U3 unit, is distributed more widely and represents a thicker sedimentary cover throughout the area. This unit consists of Oligocene\u0026ndash;Miocene sediments and appears as a single, coherent seismic package. The uppermost and youngest unit, designated as U1, is separated from the underlying units by a distinct unconformity surface. Unit U1 is typically interpreted as progradational deltaic deposits that developed on and around the shelf break and the Arkhangelsky Ridge. This unit corresponds to the youngest sedimentary sequence deposited during the Pliocene\u0026ndash;Quaternary period.\u003c/p\u003e\n\u003cp\u003eIn terms of thickness, Unit U1 reaches a maximum of approximately 0.75 s (two-way travel time) along Line 6, while Unit U2 attains about 0.5 s toward the northeastern termination of the Arkhangelsky Ridge. Additionally, the seismic sections reveal that in the shelf region\u0026mdash;particularly along Lines 2 and 6\u0026mdash;a well-defined shelf structure could not be observed. This is attributed to prolonged fluvial erosion near the coastal margins caused by river systems flowing seaward.\u003c/p\u003e\n\u003cp\u003eThe boundary of the acoustic basement observed in the seismic sections is neither continuous nor uniform, owing to its disruption by faults and its extension into deeper levels. In some profiles, this basal unit does not maintain downward continuity; instead, it locally rises upward, indicating displacement and offset resulting from faulting. Along the NE\u0026ndash;SW-oriented seismic lines (Line 2, Line 6, Line 10, and Line 11) (Fig. \u0026nbsp;6-10), which are approximately perpendicular to the Central Black Sea Ridge, three distinct fault sets cutting across different depths and stratigraphic units have been identified.\u003c/p\u003e\n\u003cp\u003eThe tectonic structures are classified as follows:\u003c/p\u003e\n\u003col start=\"1\" type=\"1\"\u003e\n \u003cli\u003e\u003cstrong\u003eFirst group faults\u003c/strong\u003e terminate within the upper portion of the acoustic basement and do not cut the overlying units. These faults are interpreted as structures that became inactive during the early Tertiary.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eSecond group faults\u003c/strong\u003e are located within Unit U1 but do not reach the seafloor. They are interpreted as syn-sedimentary faults, active contemporaneously with sedimentation.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eThird group faults\u003c/strong\u003e are observed along the southwestern and northeastern margins of the Sinop Basin. The northeastern faults delineate the boundary between the Central Black Sea Ridge and the Sinop Basin, whereas the southwestern ones are located near the shelf break. These fault systems on both sides of the basin exhibit a converging geometry and collectively resemble a negative flower structure. Based on their characteristics, the third group faults are interpreted as active fault zones (Fig. \u0026nbsp;14).\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eThe Cretaceous-aged sedimentary basement, classified as the acoustic basement in the seismic sections, has been identified at a maximum depth of approximately 4 km within the study area. Toward the Arkhangelsky Ridge, the thickness of the overlying sedimentary cover decreases to about 1 km. The most significant tectonic structures identified in the region are the fault systems that delineate the southern boundary of the Central Black Sea Ridge and the Sinop Graben. The seismic packages spanning from the Eocene to the Pliocene\u0026ndash;Quaternary have been displaced along these faults and uplifted in the profile, forming a graben-like geometry. In seismic line 11, the structure extending from the seafloor down to the acoustic basement is interpreted as a negative flower structure, typical of strike-slip fault systems (Fig. s 4 and 5). A closer examination of the ridge area reveals that the acoustic basement is well defined and overlain by three distinct stratigraphic units corresponding to the Eocene, Oligocene\u0026ndash;Miocene, and Pliocene\u0026ndash;Quaternary periods, each separated by prominent unconformity surfaces. Moreover, the stratigraphic succession atop the ridge differs in thickness from that within the displaced blocks, suggesting that the ridge units have undergone substantial erosion (Fig. \u0026nbsp;6).\u003c/p\u003e\n\u003cp\u003eWithin the region, several NW\u0026ndash;SE-trending, oblique-to strike-slip dominated tectonic lineaments of varying lengths have been identified. Three of these lineaments are aligned along the Sinop coastal margin, while the others occur along the slopes shaping the morphology of the Arkhangelsky Ridge. As these tectonic structures are located within the Sinop Basin, they have been designated SB1\u0026ndash;SB6. Faults SB1, SB2, and SB3 have been traced and interpreted along the NE\u0026ndash;SW-oriented seismic profiles. These faults intersect small submarine channel structures and are characterized by offsets that extend up to the seafloor, indicating that they are active faults with a high potential for earthquake generation.\u003c/p\u003e\n\u003cp\u003eOn NE-SW direction of Lines 2 and 6, chaotic appearance with low reflectivity and irregular reflectors are identified at the river channel border. (Fig. s 6 and 7). These structures, are sliding material observed as a result of the giant mass movement downwards especially on higher slopes that limits the canyon structures, \u0026nbsp; The sliding surface on which the sliding material slips is observed in Fig. \u0026nbsp;6e and 7. These structures appear on seismic sections as a continuous reflective surface that is smooth, horizontal, or slightly inclined due to the influence of in Line 2 (Fig. \u0026nbsp;6), the sliding material and the slip surface are observed together in the northern part of the Arkhangelsky Ridge.\u003c/p\u003e\n\u003cp\u003eAnother notable morphological feature in the region related to mass-movement processes is the presence of steep or inclined scarps formed at the initiation zones of these movements. In seismic Line 5, the structure observed at the upper boundary of the displaced mass has been identified as a head scarp (Fig. \u0026nbsp;5). This area exhibits a distinct break and steep surface, likely enhanced by the influence of faulting.\u003c/p\u003e\n\u003cp\u003eBathymetric mapping and seismic profiles from the study area reveal the presence of deep valleys incised by both active and paleo-fluvial systems. In the seismic sections, these features appear as deep depressions with laterally discontinuous and downward-inclined stratigraphic geometries, interpreted as submarine canyons or canyon floors. Two distinct canyon systems with differing depths and morphological characteristics have been identified, trending predominantly NE\u0026ndash;SW, while a third canyon-like depression extends NW\u0026ndash;SE, with depths ranging between approximately \u0026ndash;900 m and \u0026ndash;2000 m (Fig. \u0026nbsp;4).\u003c/p\u003e\n\u003cp\u003eIn the NE\u0026ndash;SW-trending Line 17, which extends parallel to both the coastline and the Arkhangelsky Ridge, a relay ramp structure was observed at the northeastern boundary of the study area, formed above a fault interpreted as buried (Fig. \u0026nbsp;11).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.3 S\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eeismicity Data Analysis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnalyses based on AFAD data, the distribution of earthquakes with Mw \u0026gt; 0 between 1900 and 2025 show that seismic activity is concentrated between the North Anatolian Fault Zone (NAFZ) and the coastal zone. (Fig. \u0026nbsp;2). Many earthquakes exceeding magnitude Mw\u0026gt;3 occurred in the study area. (Fig. \u0026nbsp;2). The depth distribution of these earthquakes indicates the existence of three separate and parallel fault segments with an uncertainty of depth approximately 35 km. Fig. \u0026nbsp;3). Although focal mechanism solutions are limited, a significant increase in the number of events detected has been observed since 2006 with the expansion of seismic stations. (Kalafat et al., 2005; Kalafat, 2017). Focal mechanism solutions are available for the earthquakes with magnitude Mw = 4.0 that occurred in the Sinop Basin in 2014 and 2025 (Fig. \u0026nbsp;2b). Epicentral analyses revealed that a distinct earthquake cluster occurred on the Arkhangelsky Ridge.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe active fault segments identified along the northeastern and southwestern coastal margins of the Sinop Basin, based on interpretations integrating seismic profiles and bathymetric contours, range between 10 km and 40 km (Fig. \u0026nbsp;4). In the coastal area of Samsun, three active strike-slip fault segments trending approximately parallel to the shoreline have been identified. In addition, three oblique to strike-slip fault segments with an approximate NE\u0026ndash;SW orientation have been mapped along the Arkhangelsky Ridge. Furthermore, these faults are estimated to be capable of generating earthquakes with magnitudes ranging from Mw 6.2 to Mw 6.97, according to Equation (1) proposed by Wells and Coppersmith (1994). Furthermore, when the faults delineated from seismic profiles are evaluated together with bathymetric data, three fault segments located between the Sinop Basin and the Mid-Black Sea Ridge, with lengths of approximately 10 km and 20 km, are interpreted to have the potential to generate earthquakes with magnitudes of Mw 6.2 and Mw 6.58. Considering that the seismogenic threshold is generally accepted as Mw \u0026ge; 6.0 (McCalpin, 2009), these faults are therefore classified as potentially hazardous.\u003c/p\u003e"},{"header":"5. Discussion","content":"\u003cp\u003e\u003cem\u003e5\u003c/em\u003e\u003cem\u003e.1\u0026nbsp;\u003c/em\u003e\u003cem\u003eBathymetric interpretations and Structural Control of the Sinop Basin\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eBased on bathymetric data, a second submarine channel located in the Yeşilırmak canyon and extending in the NNE-SSW direction is identified. (Fig. \u0026nbsp;4). This channel heads south towards the mouth of the Kızılırmak River delta. Accordingly, this channel is interpreted as a paleochannel of the Kızılırmak River, indicating that the active bed of the river shifted towards the NW over time. The tributaries of the Yeşilırmak River, which reaches the sea along the Bafra coast, have been observed to have eroded, and the seafloor morphology has been significantly disrupted in certain seismic lines (Fig. \u0026nbsp;8 and 9). \u0026nbsp;Significant deformation has also been observed in the Pliocene-Quaternary units beneath the seafloor in these areas.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFour main seismic units ranging from the Upper Cretaceous \u0026ndash; Paleocene to the Plio-Quaternary present are identified in the seismic lines. The acoustic basement unit (U4), defined as Upper Cretaceous-Paleocene, is generally cut and/or bounded by inactive faults, which are defined as the third group in our study. (Fig. \u0026nbsp;8 and 9). This accumulation was interrupted at the end of the Early Eocene by compressional tectonics resulting from the closure of Neotethys (Robinson et al., 1996; G\u0026ouml;r\u0026uuml;r et al., 1997). Therefore, the internal structure of unit U4 is wavy, sinuous and sometimes chaotic, and its contact with the overlying units is manifested by a strong reflection. This contact forms an anticline on the Arkhangelsky Ridge and a syncline beneath the Sinop Basin. This fold contact, which corresponds to the main unconformity reflection in seismic lines, is cut by several faults in many places. The U3 Unit which is symbolized by semi-horizontal reflections on the unconformity plane, presents a very thin geometry on the ridge and thickens from the edge to the middle of the basin. This unit may correspond to deposition related to the initial isolation of the Paratethys at the end of the Eocene, and the beginning of the Oligocene is characterized by the Maykop Series, which contains prominent, generally fine-grained organic-rich sediments and sandstone packages. (Simmons et al., 2018). The U3 unit, defined as Eocene unit, overlies the acoustic basement. This unit is thought to have been eroded or transported to other areas within the study area due to erosion/landslides. They are particularly visible on the Arkhangelsky Ridge in Lines 2 and 6, and below both the Arkhangelsky Rridge and Yeşilırmak canyon floors in Lines 10 and 11.\u003c/p\u003e\n\u003cp\u003eThe sediment thickness in the Black Sea Ridge is approximately 5\u0026ndash;6 km (Nikishin et al. 2003). The Sinop Basin is filled with Pliocene and Quaternary sediments that lie conformably with the basement (Meredith and Egan 2002). Rangin et al. (2002) suggested that the Sinop Basin formed as a side effect of recent movements of the North Anatolian Fault. Meredith and Egan (2002) demonstrated the existence of major extensional faults that form half-graben structures on both flanks of the Black Sea Ridge. Based on the interpretation of high-resolution seismic data, Dondurur and \u0026Ccedil;if\u0026ccedil;i (2007) indicated that the tectonic setting upper and middle continental slope of the Central Black Sea is controlled by the Arkhangelsky Ridge. Accordingly, the upper part of the ridge and the upper sediment units were affected by normal faults that formed small-scale graben structures. Dondurur and \u0026Ccedil;if\u0026ccedil;i (2007) also suggested that a second uplift formed on the northern mid-slope of the ridge. Maden and Dondurur (2013) reported that positive and negative gravity anomalies lie parallel to each other and are closely related to the tectonic structure of the region. However, according to their studies the normal fault zones surrounding the Arkhangelsky Ridge have been buried due to excessive sedimentation in the Black Sea. According to this definition, none of these fault zones show active faulting reaching to the sea floor, and therefore, earthquakes occurring in these fault zones are very unlikely to cause displacement on the sea floor. However, in this study, in all seismic lines the faults that reach and cut the seafloor in are identified and mapped. The mapped fault systems along the northeastern and southwestern margins of the Sinop basin converge downward and diverge upward, forming a characteristic negative flower structure (Fig. \u0026nbsp;10). Fig. \u0026nbsp;12 and 13 show determination of the continuity of active faults identified. Three strike-slip fault zones (sb1-3), parallel to the Sinop coast and parallel to each other, are identified. On the Arkhangelsky Ridge, NW-SE oriented oblique- to strike-slip faults (sb-4-6) that shape the ridge and indirectly affect the Central Black Sea Ridge are also mapped. Among these structures, the fault zone defined as sb6 is determined to extend along the Arkhangelsky Ridge without interruption in all sections perpendicular to the ridge and therefore the fault. However, parallel faults sb4 and sb5 are identified in the sections that cut the Archangeslky Ridge perpendicularly (Line 2, 8 and 9). These structures, as defined in the literature, are a characteristic type of structural deformation observed in the shape of a \u0026apos;V\u0026apos; due to the effect of blocks developing around the fault plane and collapsing downwards, and are evaluated as negative flower structures. Negative flower structure and reverse fault structures are also mapped in the deep seismic lines off the Cide-Sinop coast in the east of the area (İşcan et al., 2018; 2019). Considering that reverse fault structures are a type of fault formed as a result of the earth\u0026apos;s crust moving towards each other under the effect of compression forces and provided by large-scale dynamic processes of the earth, it can be interpreted that this situation occurred due to extension in our study area and compression on the Sinop-Cide side (İşcan et al., 2019).\u003c/p\u003e\n\u003cp\u003eFig. \u0026nbsp;14 shows location map of the regional tectonic lineaments. The dark blue strike-slip faults are interpreted in this study. Fault structures have been identified in seismic lines as a result of marine seismic studies and basin modeling conducted in the region (Meredith and Egan 2002; Rangin et al. 2002; Finetti et al. 1988; Cloetingh et al. 2003; Robinson et al. 1995; Robinson et al. 1996; Dondurur and \u0026Ccedil;if\u0026ccedil;i 2007). Active tectonic structures, particularly those located along the coasts of Sinop and Samsun provinces, that have not been identified in the existing literature have been observed and mapped as a result of the present study. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWhen we examine the study area on a regional scale, we can see that, in addition to strike-slip faults, reverse faults and normal faults are also active. This indicates that the Sinop basin is deformed within a right-lateral brittle shear zone. In this zone, where the North Anatolian Fault forms the main structure, east-west trending lines cause reverse/thrust faults, while northwest-southeast trending lines cause oblique faults. Accordingly, sigma 1 should be in the northwest-southeast direction, the smallest stress axis (sigma 3) should be in the northeast-southwest direction, and sigma 2 should be close to vertical. The proposed right-lateral shear zone can be tested with multidisciplinary studies.\u003c/p\u003e\n\u003cp\u003eIn previous researches, a conceptual model based on the positive flower structure developed in the North Anatolian Fault was presented (Yıldırım et al., 2013). This situation is thought to be due to the presence of a northward-trending thrust system and a negative flower structure associated with the transpressional deformation associated with the NAF. The depth of the Andrusov Ridge was observed as 14 s in the seismic sections in the study by Nikishin et al. (2014). Due to the signal penetration capacity of the seismic source equipment used in the project, the ridge structure could not be observed as depth of the ridge structure is around 4 s.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSeveral earlier studies proposed that faults bordering the Arkhangelsky Ridge and the Sinop Basin are inactive or buried beneath thick sedimentary cover. However, our seismic profiles clearly show that multiple fault segments cut Plio\u0026ndash;Quaternary units and locally offset the seafloor. These observations satisfy widely accepted criteria for active faulting, including deformation of young sediments, morphological expression on the seafloor, and spatial association with recent seismicity.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe discrepancy with earlier interpretations primarily arises from differences in data resolution and coverage. The present study employs higher-resolution seismic data and integrates bathymetric observations, allowing the detection of subtle but continuous fault-related deformation that was previously unresolved. Consequently, the southern Black Sea margin cannot be regarded as tectonically quiescent, and fault activity must be re-evaluated within a neotectonic framework.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003cstrong\u003e.2\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eSeismicity and Fault\u0026ndash;Earthquake Relationships\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study documents the geometry and length of active negative flower structures mapped offshore of Bafra and Samsun and evaluates their earthquake generating potential using the empirical relationships of Wells and Coppersmith (1994). The estimated maximum moment magnitudes range between Mw 6.2 and 6.97, indicating the capacity of these structures to generate moderate to large earthquakes. An assessment of historical seismicity together with instrumental earthquake records spanning the period 1900\u0026ndash;2025 reveals a pronounced concentration of seismic activity along the southern Black Sea margin (Fig. \u0026nbsp;2). Numerous earthquakes with magnitudes exceeding M \u0026gt; 3 have been recorded within the study area and its vicinity. Spatial analysis of epicentral distributions highlights distinct seismic clusters associated with the North Anatolian Fault Zone, the Arkhangelsky Ridge within the study area, and the boundary faults of the Sinop Basin (Fig. \u0026nbsp;2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHistorical accounts indicate that a major earthquake affecting the Amasya and \u0026Ccedil;orum regions in 1598 was followed by tsunami waves impacting the coastal sector between Sinop and Samsun (Altınok and Ersoy, 2000; Altınok et al., 2009; Nikonov, 1997). These waves reportedly propagated up to approximately 1.6 km inland, resulting in the loss of several thousand lives in coastal settlements (Ambraseys and Finkel, 1995). Additional historical sources similarly describe tsunami effects along the Sinop\u0026ndash;Samsun coastline following destructive earthquakes in the Amasya\u0026ndash;\u0026Ccedil;orum region, located east of the study area (Altınok and Ersoy, 2000).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOne of the most significant instrumental-period tsunami events documented in the Black Sea occurred after the Mw ~6.2\u0026ndash;6.5 earthquake offshore Bartın on 3 September 1968. In the aftermath of this event, tsunami wave heights of up to ~3 m were reported, with coastal inundation distances ranging between 50 and 100 m (Altınok and Ersoy, 2000). Despite these observations, the potential impacts of this and similar events on the Samsun and Bafra coastlines have not been systematically investigated. Seismic studies conducted in the Sinop Basin and along the Central Black Sea Ridge suggest the presence of active fault systems and inherited structural frameworks capable of generating large-magnitude earthquakes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRecent high-resolution seismic reflection profiles and multibeam bathymetric data provide compelling evidence for the existence of active fault systems characterized by negative and hybrid flower structures offshore of Sinop and Samsun. These structures exhibit complex kinematic behavior, incorporating strike-slip, normal, and reverse components, and thus reflect a superposition of transtensional and transpressional deformation regimes. Comparable fault systems worldwide are known to be capable of generating earthquakes with magnitudes of Mw \u0026ge; 6, underscoring the seismic significance of the identified structures. The 1939 Erzincan\u0026ndash;Fatsa earthquake (Mw 8.0) remains one of the most destructive seismic events affecting northern T\u0026uuml;rkiye, causing approximately 40,000 fatalities and more than 12,000 injuries (Jackson and McKenzie, 1988). This earthquake also triggered a tsunami along the eastern Black Sea coast, resulting in measurable shoreline modifications. At Fatsa, the coastline reportedly retreated by approximately 50 m immediately after the event and subsequently advanced by about 20 m (Eyidoğan et al., 1991). Although the Black Sea coastal region is generally regarded as an area of relatively low seismicity, historical documentation, instrumental records, and recent tectonic analyses collectively demonstrate that the regional earthquake and tsunami hazard cannot be neglected.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe spatial distribution of instrumental and historical earthquakes correlates strongly with the mapped active fault segments within and around the Sinop Basin. Earthquake clusters align with the basin-bounding strike-slip faults and with fault splays forming the negative flower structure (Fig. \u0026nbsp;2d). This spatial correspondence supports a mechanical linkage between observed seafloor faulting and regional seismicity. Although focal mechanism solutions remain limited offshore, available data indicate a combination of strike-slip and compressional components, consistent with the hybrid transtensional\u0026ndash;transpressional deformation inferred from seismic interpretation. These findings demonstrate that the Sinop Basin participates actively in the regional strain field associated with the westward motion of the Anatolian Plate and its interaction with the Central Black Sea Ridge.\u003c/p\u003e\n\u003cp\u003eThe primary tsunami-generating mechanisms in the Black Sea are associated with offshore fault rupture and secondary processes triggered by strong onshore earthquakes. In addition, submarine mass movements represent a plausible but still debated source of tsunami generation and should be considered in regional hazard assessments, particularly along the southern Black Sea margin. Given the dense population and critical infrastructure concentrated along the Samsun coastal corridor, the potential consequences of future seismic and tsunamigenic events are significant. The active submarine faults identified in this study therefore constitute a credible source for earthquakes with magnitudes exceeding Mw 6 and for associated tsunami hazards in the central Black Sea region.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003cstrong\u003e.3\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eComparison of the Sinop Basin with similar negative flower structures worldwide\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Sinop Basin is defined as a marine pull-apart basin developed between active strike-slip fault segments in the northern part of the Black Sea (Temel, 2015). Owing to its structural characteristics, the basin is comparable to other examples of negative flower structures developed in both continental and marine tectonic settings. In this section, the structural properties of the Sinop Basin are evaluated through a comparative analysis with ten pull-apart basins formed in different terrestrial and marine tectonic environments (Table 1). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Sinop Basin occupies a tectonic setting characterized by NW\u0026ndash;SE trending active oblique to strike-slip fault segments and represents the product of a predominantly transtensional deformation regime (Temel, 2015). In this respect, it exhibits strong structural similarities with pull-apart basins developed along major transform fault systems, such as the Salton Trough along the San Andreas Fault (Lachenbruch, 1985), San Diego Bay (Singleton et al., 2021), and the Alpine Fault of New Zealand (Barnes et al., 2001). Likewise, the \u0026Ccedil;ınarcık and Tekirdağ basins in the Sea of Marmara formed along the offshore segments of the North Anatolian Fault (NAF) and similarly reflect extensional deformation within a strike-slip tectonic framework (Carton et al., 2007; Pondard et al., 2007). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Sinop Basin contains an approximately 4 km\u0026ndash;thick sedimentary infill (Temel, 2015). This thickness exceeds that of relatively shallow pull-apart basins such as the Salton Trough (~2\u0026ndash;3 km; Lachenbruch, 1985) and San Diego Bay (~1\u0026ndash;2 km; Singleton et al., 2021), while remaining lower than that of deeper basins including the Dead Sea Basin (~11 km; Smit, 2008), Erzincan Basin (~6\u0026ndash;7 km; NOAA, 1939), and the Tekirdağ Basin (~5 km; Pondard et al., 2007). The marine setting of the Sinop Basin, combined with ongoing tectonic activity and deep-water conditions, provides a favorable environment for substantial sediment accumulation. The horizontal width of the Sinop Basin is estimated to range between approximately 10 and 15 km (Temel, 2015), which is comparable to the dimensions of the Kazova Basin (~5\u0026ndash;10 km; Şeng\u0026ouml;r et al., 2005), the Tekirdağ Basin (~10\u0026ndash;20 km; Pondard et al., 2007), and the Alpine Fault pull-apart basins (~15\u0026ndash;25 km; Barnes et al., 2001). This width is interpreted as the result of extensional deformation localized between strike-slip fault segments.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAn evaluation of seismicity and tectonic activity associated with the basins listed in Table 1 indicates that the Sinop Basin is situated within an active fault zone and possesses the potential to generate earthquakes of up to Mw ~6.6 (Temel, 2015). In this context, it is comparable to basins associated with major seismic events, such as the 1939 Erzincan earthquake (Mw 7.8; NOAA, 1939) and the 1999 İzmit earthquake (Mw 7.4; Pondard et al., 2007), both of which occurred in highly active strike-slip tectonic settings. Similarly, basins developed within the Andaman Sea (Diehl et al., 2013) and the Salton Trough (Lachenbruch, 1985) are located in transform fault zones characterized by elevated seismicity, suggesting a comparable tectonic risk profile to that of the Sinop Basin. The formation of the Sinop Basin is interpreted to have been governed by extensional deformation occurring between strike-slip fault segments, resulting in the development of a negative flower structure geometry (Temel, 2015). In this regard, the basin shares direct structural similarities with documented negative flower structures in the Tekirdağ Basin (Le Pichon et al., 2001), the Salton Trough (Lachenbruch, 1985), the Andaman Sea (Diehl et al., 2013), and the complex fault systems of the Sea of Marmara (Aksu et al., 2000; Armijo et al., 2005). Negative flower structures form as a consequence of extensional stress within strike-slip fault systems, where fault splays diverge upward, typically producing a pull-apart basin geometry (Sylvester, 1988; Bozkurt, 2001).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Table 1 The table summarizes and compares the key structural, morphological, and seismotectonic characteristics of terrestrial and marine pull-apart basins formed in different tectonic settings.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" align=\"\" width=\"950\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFeature\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLut Lake Basin (Terrestrial)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eErzincan Basin (Terrestrial)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eKazova Basin (Terrestrial)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSalton Trough (Terrestrial)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAndaman Sea Basin (Marine)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAlpine Fault \u0026ndash;New Zealand (Marine)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSan Diego Bay Pull-Apart/USA\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(Marine)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Ccedil;ınarcık Basin (Marine)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTekirdağ Basin (Marine)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eThis Study \u0026nbsp;(Sinop Basin)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTectonic Setting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eTranstensional pull-apart basin on the left-lateral Dead Sea Fault (Garfunkel, 1996)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eStrike-slip and extensional segment on the North Anatolian Fault (NAF) (NOAA, 1939)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eReleasing bend on the Almus segment of the NAF (Şeng\u0026ouml;r et al., 2005)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003ePull-apart basin on the San Andreas Fault Zone (Lachenbruch, 1985)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eBack-arc setting, submarine strike-slip basins (Diehl et al., 2013)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003eSubmarine releasing segment on a transform fault zone (Barnes et al., 2001)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003ePull-apart basin in a transform system linked to San Andreas (Singleton et al., 2021)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eSubmarine releasing structure on the NAF segment in the Marmara Sea (Carton et al., 2007)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eExtensional segment under the Marmara Sea along the NAF \u0026nbsp;(Pondard et al., 2007)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eBasin bounded by NW-SE active faults (Temel, 2015)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDepth / Vertical Dimension\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e~11 km of sediment, ~8 km sedimentary fill (Smit, 2008)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e~6\u0026ndash;7 km sedimentary fill (NOAA, 1939)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e~3\u0026ndash;5 km sedimentary fill (Şeng\u0026ouml;r et al., 2005)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e~2\u0026ndash;3 km deep \u0026nbsp; (Lachenbruch, 1985\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eThick sediment accumulation under seafloor (Diehl et al., 2013)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e~5\u0026ndash;6 km sedimentary fill (Barnes et al., 2001)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003eShallow basin with ~1\u0026ndash;2 km sedimentary fill (Singleton et al., 2021)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e~1200 m water + several km sediment (Carton et al., 2007)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e~1000+ m water, ~4\u0026ndash;5 km sediment (Pondard et al., 2007)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e~4 km sediment fill (Temel, 2015)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWidth / Horizontal Dimension\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e~15\u0026ndash;20 km wide, ~100 km long (Smit, 2008)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e~10 km wide, ~30 km long \u0026nbsp;(NOAA, 1939)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e~5\u0026ndash;10 km wide (NOAA, 1939)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e~10\u0026ndash;15 km wide (Crowell et al., 2013)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e~10\u0026ndash;20 km wide (Diehl et al., 2013)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e~15\u0026ndash;25 km wide \u0026nbsp;Barnes et al., 2001)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e~5\u0026ndash;10 km wide \u0026nbsp;(Singleton et al., 2021)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e~10\u0026ndash;20 km wide\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e~10\u0026ndash;20 km wide (Pondard et al., 2007)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e~10\u0026ndash;15 km wide (Temel, 2015)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSeismicity\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eModerate to large earthquakes (Garfunkel, 1996)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e1939 Erzincan Mw 7.8 earthquake (NOAA, 1939)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eModerate-scale earthquakes \u0026nbsp;Şeng\u0026ouml;r et al., (2005)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003eM6+ earthquakes on active segments (Lachenbruch, 1985)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eHigh seismicity, tsunami risk \u0026nbsp;(Diehl et al., 2013)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003eMw 7+ earthquakes; submarine surface ruptures (Howarth et al., 2018)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003eMw ~6 earthquakes with surface ruptures (USGS, 2021)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e1999 Mw 7.4 earthquake and aftershocks\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eAftershocks along active fault segments (Pondard et al., 2007)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eActive faults, potential for M6.6 earthquakes (Temel, 2015)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFormation Mechanism\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eReleasing bend with normal faults on a left-lateral fault; block subsidence (Smit, 2008)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eExtension and sedimentation through step-over on strike-slip fault (NOAA, 1939)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eGraben structure at releasing bend (Şeng\u0026ouml;r et al., 2005)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003eExtension and sedimentation in a transform fault zone (Lachenbruch, 1985)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eStrike-slip related back-arc rifting and extension (Morley, 2015)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003eReleasing bend morphology; negative flower structure on the seafloor \u0026nbsp;(Barnes et al., 2001)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003ePull-apart mechanism, graben-type depressions (Maloney, 2019)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eSubmarine releasing bend normal faults (Carton et al., 2007)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eSediment accumulation between extensional fault branches (Le Pichon et al., 2001)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eOpening between active strike-slip faults (Temel, 2015)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eSuch structures play a fundamental role in the development of major sedimentary basins, both in terms of their morphological expression and their capacity to accommodate thick sedimentary successions (\u0026Ouml;zel F\u0026uuml;z\u0026uuml;n, 2024; Turko, 2024). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe structural characteristics of the Sinop Basin closely resemble other well-documented negative flower structures developed along major strike-slip systems worldwide, including basins in the Sea of Marmara, the Dead Sea Transform, the Salton Trough, and the Andaman Sea. Similarities in basin geometry, sediment thickness, fault architecture, and seismic behavior indicate that the Sinop Basin represents a marine analogue of classic pull-apart basins formed in transtensional environments. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis comparison places the Sinop Basin within a broader geodynamic context and underscores its relevance as a natural laboratory for studying strike-slip\u0026ndash;related basin development in submarine settings. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe results discussed above demonstrate that the Sinop Basin is not a passive sedimentary depression but an actively deforming tectonic system shaped by oblique to strike-slip\u0026ndash;dominated deformation. The integration of seismic stratigraphy, fault geometry, seafloor morphology, and seismicity provides a consistent framework in which basin evolution, present-day deformation, and seismic hazard are directly linked. These findings form the basis for the conclusions presented below.\u003c/p\u003e"},{"header":"6. Conclusions ","content":"\u003cp\u003eThe integration of high-resolution multichannel seismic reflection profiles and multibeam bathymetric data reveals that the Sinop Basin is an actively deforming tectonic depression governed by the offshore extension of the North Anatolian Fault Zone. Stratigraphic analysis identifies four distinct seismic units ranging from the Eocene to the Plio-Quaternary, which have been shaped by a complex interplay of strike-slip and extensional tectonics. Interpretation of multibeam bathymetric data and multichannel high resolution seismic reflection profiles acquired in the offshore Sinop study area allowed the identification of four principal seismic units. Four main seismic units, ranging from Eocene to Plio-Quaternary, were identified and correlated across the basin. The lowermost unit is interpreted as the acoustic basement, whereas the overlying units are dated from the Eocene to the Plio\u0026ndash;Quaternary. Throughout this stratigraphic interval observed in the seismic sections, multiple deformation phases associated with active faulting have resulted in the development of uplifted ridges and anticline structures around the basin margins. Although extensional structures are dominant, well-developed anticlines affecting even the youngest sedimentary units\u0026mdash;particularly within the U1 seismic unit in the southwestern sector\u0026mdash;record localized compressional deformation indicative of a local transpressional regime. These folds are interpreted to have formed either prior to or contemporaneously with transtensional deformation. Accordingly, while the overall bathymetric expression of the basin is characterized by a pull-apart depression morphology, the structural architecture indicates that it should also be considered a negative flower structure.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBathymetric and seismic data demonstrate that the basin has developed a complex submarine morphology controlled by active tectonic deformation associated with the offshore continuation of the North Anatolian Fault Zone. The steeply dipping strike-slip fault zones bounding the basin along its northeastern and southwestern margins merge at depth and splay upward, forming a palm-shaped geometry characteristic of negative flower structures (Fig. 15). Figure 15 shows 3D block model of the study area showing batymetric, stratigraphic and structural features of Sinop basin. This structural configuration indicates that the basin evolved under a predominantly transtensional tectonic regime, in which strike-slip motion and extensional deformation acted simultaneously, consistent with development within releasing bends of a major strike-slip fault system.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSeismic sections show that the marine study area is intensely deformed by active faulting. Three distinct fault types have been identified in the region, and the active fault groups were systematically traced and mapped in detail on the seismic profiles. Among these, reverse faults constitute the second group of active faults. These reverse faults are identified by the upward displacement of reflectors on one side of the fault relative to the other. Based on this geometry, the affected branch is interpreted as a probable former (paleo-) channel. This observation suggests a progressive northwestward migration of the active channel of the Kızılırmak River over time. Such migration is interpreted as evidence of westward tilting of the region occurring contemporaneously with fault-related uplift driven by active tectonism.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Sinop Basin exhibits strong structural similarities with other basins hosting negative flower structures developed in both continental and marine environments, in terms of its tectonic setting, sediment thickness, fault geometry, and seismic potential (Table 1). In particular, comparisons with the Tekirdağ, \u0026Ccedil;ınarcık, Salton, and Andaman basins indicate that the formation mechanism and morphology of the Sinop Basin display the characteristic features of strike-slip\u0026ndash;related pull-apart systems. Accordingly, the Sinop Basin represents a valuable natural laboratory for investigating the geodynamic evolution of pull-apart basins developed within active fault zones. Slip surfaces identified in the regional seismic data clearly indicate the presence of mechanically weak layers along which mass movement has occurred. The slip surface observed in the northern sector of the Arkhangelsky Ridge, in particular, suggests that mass movements in this area were dominated by lateral sliding mechanisms. This observation confirms the complex nature of deformation and the presence of structurally controlled weak zones within the basin. The continuity of these slip surfaces provides important constraints for identifying mechanically weak domains and for assessing the potential risk of submarine landslides or large-scale mass movement processes.\u003c/p\u003e\n\u003cp\u003eOverall, this study challenges previous interpretations that regarded the southern Black Sea margin as tectonically quiescent. Instead, it demonstrates that the Sinop Basin represents an active component of the regional neotectonic framework and should be incorporated into future seismic and coastal hazard assessments. The Sinop Basin thus provides a key example of strike-slip\u0026ndash;related basin development in a submarine setting and contributes to a broader understanding of deformation processes along continental margins. Collectively this study provides the first integrated geophysical evidence that the Sinop Basin is located in actively deforming strike-slip system with significant seismic hazard implications for the southern Black Sea margin.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBy reconciling the dominant transtensional geometry (negative flower structure) with localized compressional features (transpression), this aligns well with modern structural interpretations of evolving strike-slip basins. The inclusion of the Kızılırmak paleo-channel migration serves as compelling independent evidence, effectively linking deep-seated structural deformation (tilting and uplift) to surface geomorphological processes. Furthermore, placing the basin in the context of major global analogues, such as the Sea of Marmara and Salton Trough, validates the proposed kinematic model and substantiates the challenge to the region\u0026apos;s historical interpretation as tectonically quiescent.\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFinancing Statement\u003c/h2\u003e\n\u003cp\u003eThis study is financially supported by 7th European Marie-Curie ITN 607996 no. Anatolian pLateau climatE and Tectonic Hazards (ALErT) Project.\u003c/p\u003e\n\u003ch2\u003eConflict of Interest Statement\u003c/h2\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eS.\u0026Ouml;. , G.\u0026Ccedil;., H.S. ,S.O. wrote the main manuscript text \u0026Ouml;.B. prepared figures\u0026Ouml;.C prepared figuresC.E. prepared figures\u0026Ouml;.\u0026Ouml;. and O.A. data collection1-9 All authors reviewed the manuscript\u003c/p\u003e\n\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eThis study constitutes part of the PhD thesis of Sevin\u0026ccedil; \u0026Ouml;zel F\u0026uuml;z\u0026uuml;n. The multichannel seismic and multibeam bathmetry data presented in this article were collected within the framework of the 7th European Marie-Curie ITN Anatolian pLateau climatE and Tectonic Hazards (ALErT) Project. Data processing was carried out using the facilities of the Marine Geophysics Laboratory (SeisLab), affiliated with the Institute of Marine Sciences and Technology, Dokuz Eyl\u0026uuml;l University. We are deeply indebted to the State Planning Organization (DPT) for their invaluable support in procuring equipment and establishing the data acquisition, processing and interpretation SeisLab through project 2003K120360. Furthermore, we would like to express our profound appreciation to SEAMAP company for their technical support regarding the laboratory instrumentation utilized during marine data acquisition campaigns. Also, we would like to thank Europe Commission, European Marine Observation and Data Network (EMODnet Geology) for their excellent cooperation.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eThe authors do not have permission to share data.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAjala R, Persaud P, Stock JM, Fuis GS, Hole JA, Goldman M, Scheirer D (2019) Three-dimensional basin and fault structure from a detailed seismic velocity model of Coachella Valley, Southern California. \u003cem\u003eJ Geophys Res Solid Earth\u003c/em\u003e 124(5):4728\u0026ndash;4750. https://doi.org/10.1029/2018JB016260\u003c/li\u003e\n \u003cli\u003eAksoy E, İnce\u0026ouml;z M, Ko\u0026ccedil;yiğit A (2007) Lake Hazar Basin: a negative flower structure on the East Anatolian Fault System (EAFS), SE T\u0026uuml;rkiye. \u003cem\u003eTurk J Earth Sci\u003c/em\u003e 16(3):319\u0026ndash;338\u003c/li\u003e\n \u003cli\u003eAlgan O, G\u0026ouml;kaşan E, Gazioğlu ZY, Y\u0026uuml;cel B, Alpar B, G\u0026uuml;neysu C, Kırcı E, Demirel S, Sarı E, Ongan D (2002) A high-resolution seismic study in Sakarya Delta and Submarine Canyon, southern Black Sea shelf. \u003cem\u003eCont Shelf Res\u003c/em\u003e 22(10):1511\u0026ndash;1527. https://doi.org/10.1016/S0278-4343(02)00012-2\u003c/li\u003e\n \u003cli\u003eAltınok Y, Alpar B, \u0026Ouml;zer N, \u0026Uuml;nl\u0026uuml; S, Meri\u0026ccedil; E, Nazik A, Avşar N, Balkıs N, Aykurt H, Taş S (2009) Black Sea tsunamis and paleotsunami studies on the Thrace Coasts of Turkey. In: \u003cem\u003eProceedings of MEDCOAST 2009 International Conference\u003c/em\u003e, Sochi, Russia, 10\u0026ndash;14 November 2009, pp 931\u0026ndash;942\u003c/li\u003e\n \u003cli\u003eAltınok Y, Ersoy Ş (2000) Tsunamis observed on and near the Turkish coast. \u003cem\u003eNat Hazards\u003c/em\u003e 21:185\u0026ndash;205. https://doi.org/10.1023/A:1008130512498\u003c/li\u003e\n \u003cli\u003eAmbraseys NN, Finkel CA (1995) \u003cem\u003eThe seismicity of Turkey and adjacent areas: a historical review: 1500\u0026ndash;1800\u003c/em\u003e. Eren Yayıncılık, İstanbul\u003c/li\u003e\n \u003cli\u003eArmijo R, Pondard N, Meyer B, U\u0026ccedil;arkuş G, de L\u0026eacute;pinay BM, Malavieille J, Dominguez S, Gustcher MA, Schmidt S, Beck C et al (2005) Submarine fault scarps in the Sea of Marmara pull-apart (North Anatolian Fault): implications for seismic hazard in Istanbul. \u003cem\u003eGeochem Geophys Geosyst\u003c/em\u003e 6(6):Q06009. https://doi.org/10.1029/2004GC000896\u003c/li\u003e\n \u003cli\u003eBarka AA, Kadinsky-Cade K (1988) Strike-slip fault geometry in T\u0026uuml;rkiye and its influence on earthquake activity. \u003cem\u003eTectonics\u003c/em\u003e 7(3):663\u0026ndash;684. https://doi.org/10.1029/TC007i003p00663\u003c/li\u003e\n \u003cli\u003eBen-Avraham Z, Ten Brink US (1989) Transverse faults and segmentation of strike-slip faults: examples from the Dead Sea Transform. \u003cem\u003eTectonophysics\u003c/em\u003e 180:37\u0026ndash;47. https://doi.org/10.1016/0040-1951(90)90370-N\u003c/li\u003e\n \u003cli\u003eBozkurt E, Ko\u0026ccedil;yiğit A (1996) The Kazova basin: an active negative flower structure on the Almus Fault Zone, a splay fault system of the North Anatolian Fault Zone, T\u0026uuml;rkiye. \u003cem\u003eTectonophysics\u003c/em\u003e 265(1\u0026ndash;2):239\u0026ndash;254. https://doi.org/10.1016/S0040-1951(96)00045-5\u003c/li\u003e\n \u003cli\u003eBrothers DS, Harding AJ, Babcock JM (2009) Tectonic evolution of the Salton Sea inferred from seismic reflection data. \u003cem\u003eNat Geosci\u003c/em\u003e 2(8):581\u0026ndash;584. https://doi.org/10.1038/ngeo590\u003c/li\u003e\n \u003cli\u003eChristie-Blick N, Biddle KT (1985) Deformation and basin formation along strike-slip faults. In: Biddle KT, Christie-Blick N (eds) \u003cem\u003eStrike-slip deformation, basin formation, and sedimentation\u003c/em\u003e. SEPM Special Publication 37, pp 1\u0026ndash;34\u003c/li\u003e\n \u003cli\u003eCurray JR (2005) Tectonics and history of the Andaman Sea region. \u003cem\u003eJ Asian Earth Sci\u003c/em\u003e 25(1):187\u0026ndash;232. https://doi.org/10.1016/j.jseaes.2004.09.001\u003c/li\u003e\n \u003cli\u003eDondurur D, \u0026Ccedil;if\u0026ccedil;i G (2007) Acoustic structure and recent sediment transport processes on the continental slope of Yeşilırmak River fan, Eastern Black Sea. \u003cem\u003eMar Geol\u003c/em\u003e 237(1\u0026ndash;2):37\u0026ndash;53. https://doi.org/10.1016/j.margeo.2006.10.035\u003c/li\u003e\n \u003cli\u003eDondurur D, \u0026Ccedil;if\u0026ccedil;i G (2007) Acoustic evidence of shallow gas and gas hydrates in the Black Sea sediments off the coast of Samsun. \u003cem\u003eGeo-Marine Letters\u003c/em\u003e 27:311\u0026ndash;320. https://doi.org/10.1007/s00367-007-0084-9\u003c/li\u003e\n \u003cli\u003eDondurur D, K\u0026uuml;\u0026ccedil;\u0026uuml;k HM, \u0026Ccedil;if\u0026ccedil;i G (2013) Quaternary mass wasting on the western Black Sea margin, offshore of Amasra. \u003cem\u003eGlob Planet Change\u003c/em\u003e 103:248\u0026ndash;260. https://doi.org/10.1016/j.gloplacha.2012.05.009\u003c/li\u003e\n \u003cli\u003eElmas A, Karslı H (2021) Tectonic and crustal structure of Arkhangelsky ridge using Bouguer gravity data. \u003cem\u003eMar Geophys Res\u003c/em\u003e 42:21. https://doi.org/10.1007/s11001-021-09443-z\u003c/li\u003e\n \u003cli\u003eFialko Y (2006) Interseismic strain accumulation and the earthquake potential on the southern San Andreas fault system. \u003cem\u003eNature\u003c/em\u003e 441(7096):968\u0026ndash;971. https://doi.org/10.1038/nature04797\u003c/li\u003e\n \u003cli\u003eFinetti I, Bricchi G, Ben AD, Pipan M, Xuan Z (1988) Geophysical study of the Black Sea. \u003cem\u003eBoll Geofis Teor Appl\u003c/em\u003e 30(117):197\u0026ndash;324\u003c/li\u003e\n \u003cli\u003eGarfunkel Z, Ben-Avraham Z (1996) The structure of the Dead Sea basin. \u003cem\u003eTectonophysics\u003c/em\u003e 266(1\u0026ndash;4):155\u0026ndash;176. https://doi.org/10.1016/S0040-1951(96)00188-6\u003c/li\u003e\n \u003cli\u003eGartman A, Hein JR (2019) Mineralization at oceanic transform faults and fracture zones. In: Duarte JC (ed) \u003cem\u003eTransform Plate Boundaries and Fracture Zones\u003c/em\u003e. Elsevier, pp 105\u0026ndash;118. https://doi.org/10.1016/B978-0-12-812064-4.00005-0\u003c/li\u003e\n \u003cli\u003eG\u0026ouml;r\u0026uuml;r N (1988) Timing of opening of the Black Sea basin. \u003cem\u003eTectonophysics\u003c/em\u003e 147(3\u0026ndash;4):247\u0026ndash;262. https://doi.org/10.1016/0040-1951(88)90189-8\u003c/li\u003e\n \u003cli\u003eG\u0026ouml;r\u0026uuml;r N, Monod O, Okay AI, Şeng\u0026ouml;r AMC, T\u0026uuml;ys\u0026uuml;z O, Yiğitbaş E, Sakın\u0026ccedil; M, Akk\u0026ouml;k R (1997) Palaeogeographic and tectonic position of the Carboniferous rocks of the Western Pontides (T\u0026uuml;rkiye) in the frame of the Variscan belt. \u003cem\u003eBull Soc G\u0026eacute;ol Fr\u003c/em\u003e 168(2):197\u0026ndash;205\u003c/li\u003e\n \u003cli\u003eGraham R, Kaymakci N, Horn B (2013) Revealing the mysteries of the Black Sea. \u003cem\u003eGEO ExPro\u003c/em\u003e 10(5):58\u0026ndash;63\u003c/li\u003e\n \u003cli\u003eHarding TP (1985) Seismic characteristics and identification of negative flower structures, positive flower structures, and positive structural inversion. \u003cem\u003eAAPG Bull\u003c/em\u003e 69(4):582\u0026ndash;600. https://doi.org/10.1306/AD462538-16F7-11D7-8645000102C1865D\u003c/li\u003e\n \u003cli\u003eHarris PT, Macmillan-Lawler M, Rupp J, Baker EK (2014) Geomorphology of the oceans. \u003cem\u003eMar Geol\u003c/em\u003e 352:4\u0026ndash;24. https://doi.org/10.1016/j.margeo.2014.01.011\u003c/li\u003e\n \u003cli\u003eHaşimoğlu BY, \u0026Ccedil;if\u0026ccedil;i G, Lacassin R, Fern\u0026aacute;ndez-Blanco D, \u0026Ouml;zel \u0026Ouml; (2016) Tectonics of the Kızılırmak delta and Sinop Basin offshore Pontides, evidence from new high-resolution seismic and bathymetric data. Paper presented at the \u003cem\u003eAGU Fall Meeting 2016\u003c/em\u003e, San Francisco, USA, 12\u0026ndash;16 December 2016\u003c/li\u003e\n \u003cli\u003eHuang Q, Liu Y (2017) Hybrid flower structures in strike-slip fault systems: insights from sandbox modeling. \u003cem\u003eTectonophysics\u003c/em\u003e 721:237\u0026ndash;251. https://doi.org/10.1016/j.tecto.2017.10.017\u003c/li\u003e\n \u003cli\u003eHubert A, Garcia D, Moernaut J, Van Daele M, Damci E, Cagatay N, De Batist M (2008) The Hazar pull-apart along the East Anatolian Fault: structure and active deformation. Paper presented at the \u003cem\u003eTectonic Studies Group Annual Meeting\u003c/em\u003e, La Roche-en-Ardenne, Belgium, 8\u0026ndash;10 January 2008\u003c/li\u003e\n \u003cli\u003eJipa DC, Panin N (2020) Narrow shelf canyons vs. wide shelf canyons: two distinct types of Black Sea submarine canyons. \u003cem\u003eQuat Int\u003c/em\u003e 540:120\u0026ndash;136. https://doi.org/10.1016/j.quaint.2018.08.006\u003c/li\u003e\n \u003cli\u003eJipa DC, Panin N, Olariu C, Pop C (2020) Black Sea submarine valleys\u0026mdash;patterns, systems, networks. \u003cem\u003eGeo-Eco-Marina\u003c/em\u003e 26:15\u0026ndash;40. https://doi.org/10.5281/zenodo.4682752\u003c/li\u003e\n \u003cli\u003eKalafat D (2017) Seismicity and tectonics of the Black Sea. \u003cem\u003eInt J Earth Sci Geophys\u003c/em\u003e 3(11):1\u0026ndash;8. https://doi.org/10.35840/2631-5033/1811\u003c/li\u003e\n \u003cli\u003eKalafat D, G\u0026uuml;neş Y, Kara M, Deniz P, Kekovalı K, Kuleli HS, G\u0026uuml;len L, Yılmazer M, \u0026Ouml;zel NM (2007) \u003cem\u003eA revised and extended earthquake catalogue for T\u0026uuml;rkiye since 1900 (M \u0026ge; 4.0)\u003c/em\u003e. Boğazi\u0026ccedil;i University, Kandilli Observatory and Earthquake Research Institute, İstanbul (Report)\u003c/li\u003e\n \u003cli\u003eKennedy MP, Clarke SH (1999) Analysis of late Quaternary faulting in San Diego Bay and hazard implications for the San Diego region, California. \u003cem\u003eBull Seismol Soc Am\u003c/em\u003e 89(6):1465\u0026ndash;1477\u003c/li\u003e\n \u003cli\u003eLe Pichon X, Chamot-Rooke N, Lallemant S (2001) The Western Mediterranean Basin. \u003cem\u003eJ Geophys Res Solid Earth\u003c/em\u003e 106(B8):16119\u0026ndash;16130. https://doi.org/10.1029/2000JB900403\u003c/li\u003e\n \u003cli\u003eLericolais G, Popescu I, Guichard F, Popescu SM (2011) Assessment of Black Sea water-level fluctuations since the Last Glacial Maximum based on seismic and core data. \u003cem\u003eMarine Geology\u003c/em\u003e 284:1\u0026ndash;16. https://doi.org/10.1016/j.margeo.2011.03.003\u003c/li\u003e\n \u003cli\u003eLetouzey J, Biju-Duval B, Dorkel A, Gonnard R, Krischev K, Montadert L, Sungurlu O (1977) The Black Sea: a marginal basin\u0026mdash;geophysical and geological data. In: Biju-Duval B, Montadert L (eds) \u003cem\u003eStructural History of the Mediterranean Basins\u003c/em\u003e. Editions Technip, Paris, pp 363\u0026ndash;376\u003c/li\u003e\n \u003cli\u003eMaden N, \u0026Ouml;zt\u0026uuml;rk S (2015) Seismic b-values, Bouguer gravity and heat flow data beneath Eastern Anatolia, T\u0026uuml;rkiye: tectonic implications. \u003cem\u003eSurv Geophys\u003c/em\u003e 36:549\u0026ndash;570. https://doi.org/10.1007/s10712-015-9327-1\u003c/li\u003e\n \u003cli\u003eMaloney JM, Driscoll NW, Kent G, Duke S, Freeman T, Bormann JM (2016) Segmentation and step-overs along strike-slip fault systems in the inner California borderlands: implications for fault architecture and basin formation. In: \u003cem\u003eApplied Geology in California\u003c/em\u003e, Environmental Engineering Geologists 26, pp 655\u0026ndash;677\u003c/li\u003e\n \u003cli\u003eMcCalpin JP (2009) \u003cem\u003ePaleoseismology\u003c/em\u003e, 2nd edn. Academic Press\u003c/li\u003e\n \u003cli\u003eMechie J, Abu-Ayyash K, Ben-Avraham Z, El-Kelani R, Qabbani I, Weber M, DESIRE Group (2009) Crustal structure of the southern Dead Sea basin derived from project DESIRE wide-angle seismic data. \u003cem\u003eGeophys J Int\u003c/em\u003e 178(1):457\u0026ndash;478. https://doi.org/10.1111/j.1365-246X.2009.04161.x\u003c/li\u003e\n \u003cli\u003eMeisner LB, Tugolesov DA (2003) Basic reflections from sedimentary filling of Black Sea depression (correlation and stratigraphic tying). \u003cem\u003eStratigr Geol Correl\u003c/em\u003e 11(6):595\u0026ndash;608\u003c/li\u003e\n \u003cli\u003eMeredith DJ, Egan SS (2002) The geological and geodynamic evolution of the Eastern Black Sea Basin: insights from 2-D and 3-D tectonic modelling. \u003cem\u003eTectonophysics\u003c/em\u003e 350(2):157\u0026ndash;179. https://doi.org/10.1016/S0040-1951(02)00121-X\u003c/li\u003e\n \u003cli\u003eMunteanu I, Matenco L, Dinu C, Cloetingh S (2011) Kinematics of back-arc inversion of the Western Black Sea basin. \u003cem\u003eTectonics\u003c/em\u003e 30(5):TC5004. https://doi.org/10.1029/2011TC002865\u003c/li\u003e\n \u003cli\u003eNikonov A (1997) Tsunami\u0026mdash;A threat from the south? \u003cem\u003eSearch and Development, Science in Russia\u003c/em\u003e 6:13\u0026ndash;19\u003c/li\u003e\n \u003cli\u003eNikishin AM, Okay AI, T\u0026uuml;ys\u0026uuml;z O, Demirer A, Wannier M, Amelin N, Petrov E (2015) The Black Sea basins structure and history: new model based on new deep penetration regional seismic data. Part 2: tectonic history and palaeogeography. \u003cem\u003eMar Pet Geol\u003c/em\u003e 59:656\u0026ndash;670. https://doi.org/10.1016/j.marpetgeo.2014.08.018\u003c/li\u003e\n \u003cli\u003eOaie G, Seghedi A, Rădulescu V (2016) Natural marine hazards in the Black Sea and the system of their monitoring and real-time warning. \u003cem\u003eGeo-Eco-Marina\u003c/em\u003e 22:5\u0026ndash;28. https://doi.org/10.5281/zenodo.889593\u003c/li\u003e\n \u003cli\u003eOcakoğlu N, İşcan Y, G\u0026uuml;l FK (2022) Mapping onland river channels up to the seafloor along offshore Cide-Sinop in the Southern Black Sea from the perspective of the Black Sea flooding. \u003cem\u003eInt J Environ Geoinformatics\u003c/em\u003e 9(1):116\u0026ndash;126. https://doi.org/10.30897/ijegeo.948042\u003c/li\u003e\n \u003cli\u003eOcakoğlu N, İşcan Y, Kılı\u0026ccedil; Y, \u0026Ouml;zel O (2018) Morphologic and seismic evidence of rapid submergence offshore Cide-Sinop in the southern Black Sea shelf. \u003cem\u003eGeomorphology\u003c/em\u003e 311:76\u0026ndash;89. https://doi.org/10.1016/j.geomorph.2018.03.008\u003c/li\u003e\n \u003cli\u003eOkay AI, Şeng\u0026ouml;r AMC, G\u0026ouml;r\u0026uuml;r N (1994) Kinematic history of the opening of the Black Sea and its effect on the surrounding regions. \u003cem\u003eGeology\u003c/em\u003e 22(3):267\u0026ndash;270. https://doi.org/10.1130/0091-7613(1994)022\u0026lt;0267:KHOTOO\u0026gt;2.3.CO;2\u003c/li\u003e\n \u003cli\u003e\u0026Ouml;zel F\u0026uuml;z\u0026uuml;n, S. (2024l). \u003cem\u003eInvestigation Of Mid-Black Sea Ridge/Sinop trough with marine geophysical methods\u003c/em\u003e. PhD Thesis, (Publication No. 905319) Dokuz Eyl\u0026uuml;l University The Graduate School of Natural and Applied Sciences , İzmir, T\u0026uuml;rkiye.\u003c/li\u003e\n \u003cli\u003e\u0026Ouml;zel F\u0026uuml;z\u0026uuml;n S, \u0026Ccedil;if\u0026ccedil;i G, S\u0026ouml;zbilir H, Okay G\u0026uuml;naydın S, Atgın O, \u0026Ouml;zel \u0026Ouml; (2024) Stratigraphic and structural features of the Sinop Basin close to the Mid Black Sea Ridge using multi-channel seismic and multibeam bathymetric data. \u003cem\u003eRecep Tayyip Erdoğan University Journal of Science and Engineering\u003c/em\u003e 5:49\u0026ndash;59. https://doi.org/10.53501/rteufemud.1469379\u003c/li\u003e\n \u003cli\u003ePanin N, Ion E, Ion G (1997) \u003cem\u003eBlack Sea GIS\u003c/em\u003e (CD-ROM). GEF Black Sea Environmental Programme\u003c/li\u003e\n \u003cli\u003ePanin N, Jipa D (2002) Danube River sediment input and its interaction with the North-western Black Sea. \u003cem\u003eEstuar Coast Shelf Sci\u003c/em\u003e 54(3):551\u0026ndash;562. https://doi.org/10.1006/ecss.2000.0664\u003c/li\u003e\n \u003cli\u003ePondard N, Armijo R, King GCP, Meyer B, Flerit F (2007) Fault interactions in the Sea of Marmara pull-apart (North Anatolian Fault): earthquake clustering and propagating earthquake sequences. \u003cem\u003eGeophys J Int\u003c/em\u003e 171(3):1185\u0026ndash;1197. https://doi.org/10.1111/j.1365-246X.2007.03580.x\u003c/li\u003e\n \u003cli\u003ePopescu I (2002) Analyse des processus s\u0026eacute;dimentaires r\u0026eacute;cents dans l\u0026apos;\u0026eacute;ventail profond du Danube (mer noire) [Analysis of recent sedimentary processes in the Danube deep-sea fan (Black Sea)]. PhD thesis, Universit\u0026eacute; de Bretagne Occidentale, Brest, France \u0026amp; University of Bucharest, Bucharest, Romania, 282 pp. Available at: http://www.theses.fr/2002BRES2012\u003c/li\u003e\n \u003cli\u003ePopescu I (2008) Processus s\u0026eacute;dimentaires r\u0026eacute;cents dans l\u0026rsquo;\u0026eacute;ventail profond du Danube (Mer Noire) [Recent sedimentary processes in the Danube deep-sea fan (Black Sea)]. \u003cem\u003eGeo-Eco-Marina\u003c/em\u003e 15(Special Publication 2):202 pp\u003c/li\u003e\n \u003cli\u003ePopescu I, Lericolais G, Panin N, Normand A, Dinu C, Le Drezen E (2004) The Danube submarine canyon (Black Sea): morphology and sedimentary processes. \u003cem\u003eMar Geol\u003c/em\u003e 206:249\u0026ndash;265. https://doi.org/10.1016/j.margeo.2004.03.003\u003c/li\u003e\n \u003cli\u003ePopescu I, Panin N, Jipa D, Lericolais G, Ion G (2015) Submarine canyons of the Black Sea basin. In: Briand F (ed) \u003cem\u003eSubmarine Canyons of the Mediterranean Sea and the Black Sea\u003c/em\u003e, CIESM Monograph 47, Monaco, pp 143\u0026ndash;152.\u003c/li\u003e\n \u003cli\u003eRacano S, Schildgen T, Ballato P, Yıldırım C, Wittmann H (2023) Rock-uplift history of the Central Pontides from river-profile inversions and implications for development of the North Anatolian Fault. \u003cem\u003eEarth Planet Sci Lett\u003c/em\u003e 616:118231. https://doi.org/10.1016/j.epsl.2023.118231\u003c/li\u003e\n \u003cli\u003eRangin C, Bader AG, Pascal G, Ecevitoğlu B, G\u0026ouml;r\u0026uuml;r N (2002) Deep structure of the Mid Black Sea High (offshore T\u0026uuml;rkiye) imaged by multi-channel seismic survey (BLACKSIS cruise). \u003cem\u003eMar Geol\u003c/em\u003e 182(3\u0026ndash;4):265\u0026ndash;278. https://doi.org/10.1016/S0025-3227(01)00236-5\u003c/li\u003e\n \u003cli\u003eRobinson AG, Banks CJ, Rutherford MM, Hirst JPP (1995) Stratigraphic and structural development of the Eastern Pontides, T\u0026uuml;rkiye. \u003cem\u003eJ Geol Soc London\u003c/em\u003e 152(5):861\u0026ndash;872. https://doi.org/10.1144/gsjgs.152.5.0861\u003c/li\u003e\n \u003cli\u003eRobinson AG, Kerusov E (1997) \u003cem\u003eRegional and petroleum geology of the Black Sea and surrounding region\u003c/em\u003e. American Association of Petroleum Geologists\u003c/li\u003e\n \u003cli\u003eRobinson AG, Rudat JH, Banks CJ, Wiles RLF (1996) Petroleum geology of the Black Sea. \u003cem\u003eMar Pet Geol\u003c/em\u003e 13(2):195\u0026ndash;223. https://doi.org/10.1016/0264-8172(95)00042-9\u003c/li\u003e\n \u003cli\u003eRoss DA, Uchupi E, Prada KE, MacIlvaine JC (1974) Bathymetry and microphotography of Black Sea. American Association of Petroleum Geologists\u003c/li\u003e\n \u003cli\u003eSalcher BC, Meurers B, Decker K, H\u0026ouml;lzel M, Wagreich M (2012) Strike-slip tectonics and Quaternary basin formation along the Vienna Basin fault system inferred from Bouguer gravity derivatives. \u003cem\u003eTectonics\u003c/em\u003e 31(3):TC3005. https://doi.org/10.1029/2011TC002979\u003c/li\u003e\n \u003cli\u003eSchleder Z, Krezsek C, Turi V, Tari G, Kosi W, Fallah M (2015) Regional structure of the Western Black Sea Basin: constraints from cross-section balancing. In: Post PJ, Coleman JJ et al (eds) \u003cem\u003ePetroleum systems in \u0026ldquo;Rift\u0026rdquo; basins\u003c/em\u003e. GCSSEPM Foundation, pp 396\u0026ndash;411. https://doi.org/10.5724/gcs.15.34.0396\u003c/li\u003e\n \u003cli\u003eSeeber L, Armbruster JG (2000) Earthquakes and asperities in the transition fault of the Marmara Sea: possible source of the next great earthquake. \u003cem\u003eSeismol Res Lett\u003c/em\u003e 71(3):374\u0026ndash;388. https://doi.org/10.1785/gssrl.71.3.374\u003c/li\u003e\n \u003cli\u003eSimmons MD, Tari GC, Okay AI (2018) Petroleum geology of the Black Sea: introduction. \u003cem\u003eGeol Soc London Spec Publ\u003c/em\u003e 464:1\u0026ndash;18. https://doi.org/10.1144/SP464.16\u003c/li\u003e\n \u003cli\u003eSingh SC, Moeremans R (2017) Anatomy of the Andaman\u0026ndash;Nicobar subduction system from seismic reflection data. \u003cem\u003eGeol Soc London Mem\u003c/em\u003e 47(1):193\u0026ndash;204. https://doi.org/10.1144/M47.13\u003c/li\u003e\n \u003cli\u003eSingleton DM, Maloney JM, Brothers DS, Klotsko S, Driscoll NW, Rockwell TK (2021) Pull-apart basin, fault structure, marine paleoseismology, marine geophysics in the Newport-Inglewood\u0026ndash;Rose Canyon fault system, inner California continental borderland, San Diego Bay. \u003cem\u003eFront Earth Sci\u003c/em\u003e 9:641346. https://doi.org/10.3389/feart.2021.641346\u003c/li\u003e\n \u003cli\u003eSipahioğlu NO, Karahanoğlu N, Altıner D (2013) Analysis of Plio-Quaternary deep marine systems and their evolution in a compressional tectonic regime, Eastern Black Sea Basin. \u003cem\u003eMar Pet Geol\u003c/em\u003e 43:187\u0026ndash;207. https://doi.org/10.1016/j.marpetgeo.2013.02.008\u003c/li\u003e\n \u003cli\u003eSmit J, Brun JP, Cloetingh S, Ben-Avraham Z (2008) Pull-apart basin formation and development in narrow transform zones with application to the Dead Sea Basin. \u003cem\u003eTectonics\u003c/em\u003e 27(6):TC6018. https://doi.org/10.1029/2007TC002119\u003c/li\u003e\n \u003cli\u003eSofta M, Emre T, S\u0026ouml;zbilir H, Spencer JQ, Turan M (2018) Geomorphic evidence for active tectonic deformation in the coastal part of Eastern Black Sea, Eastern Pontides, T\u0026uuml;rkiye. \u003cem\u003eGeodin Acta\u003c/em\u003e 30(1):249\u0026ndash;264. https://doi.org/10.1080/09853111.2018.1494776\u003c/li\u003e\n \u003cli\u003eSofta M, Spencer JQ, S\u0026ouml;zbilir H, Huot S, Emre T (2021) Luminescence dating of Quaternary marine terraces from the coastal part of Eastern Black Sea and their tectonic implications for the Eastern Pontides, T\u0026uuml;rkiye. \u003cem\u003eTurk J Earth Sci\u003c/em\u003e 30(3):359\u0026ndash;378. https://doi.org/10.3906/yer-2005-21\u003c/li\u003e\n \u003cli\u003eSomoza L, Medialdea T, Terrinha P, Ramos A, V\u0026aacute;zquez JT (2021) Submarine active faults and morphotectonics around the Iberian margins: seismic and tsunami hazards. \u003cem\u003eFront Earth Sci\u003c/em\u003e 9:653639. https://doi.org/10.3389/feart.2021.653639\u003c/li\u003e\n \u003cli\u003eSylvester AG (1988) Strike-slip faults. \u003cem\u003eGeol Soc Am Bull\u003c/em\u003e 100(11):1666\u0026ndash;1703. https://doi.org/10.1130/0016-7606(1988)100\u0026lt;1666:SSF\u0026gt;2.3.CO;2\u003c/li\u003e\n \u003cli\u003eTari G, Fallah M, Kosi W, Schleder Z, Turi V, Krezsek C (2015) Regional rift structure of the Western Black Sea Basin: map-view kinematics. Paper presented at the \u003cem\u003e34th Annual GCSSEPM Foundation Perkins-Rosen Research Conference\u003c/em\u003e, Houston, USA, 13\u0026ndash;16 December 2015\u003c/li\u003e\n \u003cli\u003eTari GC, Simmons MD (2018) History of deepwater exploration in the Black Sea and an overview of deepwater petroleum play types. \u003cem\u003eGeol Soc London Spec Publ\u003c/em\u003e 464:439\u0026ndash;475. https://doi.org/10.1144/SP464.16\u003c/li\u003e\n \u003cli\u003eThierry S, Dick S, George S, Benoit L, Cyrille P (2019) EMODnet bathymetry: a compilation of bathymetric data in the European waters. Paper presented at \u003cem\u003eOCEANS 2019\u003c/em\u003e, Marseille, France, 17\u0026ndash;20 June 2019\u003c/li\u003e\n \u003cli\u003eTugolesov DA, Gorshkov AS, Meysner LB, Soloviov VV, Khakhalev EM, Akilova YuV, Akentieva GP, Gabidulina TI, Kolomeytseva SA, Kochneva TYu, Pereturina IG, Plashihina IN (1985) \u003cem\u003eTectonics of the Mesozoic sediments of the Black Sea Basin\u003c/em\u003e. Nedra, Moscow (in Russian), 215 pp\u003c/li\u003e\n \u003cli\u003eTurko M (2024) Strike-slip kinematics for pop-ups and pull-aparts. \u003cem\u003eGeoExPro Magazine\u003c/em\u003e. https://geoexpro.com/strike-slip-kinematics-for-pop-ups-and-pull-aparts/. Accessed 10 Sep 2024\u003c/li\u003e\n \u003cli\u003eU.S. Geological Survey (2014) SRTM 1 Arc-Second Global (30 m) [Digital Elevation Model]. U.S. Geological Survey. https://earthexplorer.usgs.gov\u003c/li\u003e\n \u003cli\u003eWei EA, Holmes JJ, Driscoll NW (2020) Strike-slip transpressional uplift offshore San Onofre, California inhibits sediment delivery to the deep sea. \u003cem\u003eFront Earth Sci\u003c/em\u003e 8:51. https://doi.org/10.3389/feart.2020.00051\u003c/li\u003e\n \u003cli\u003eWells DL, Coppersmith KJ (1994) New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. \u003cem\u003eBull Seismol Soc Am\u003c/em\u003e 84(4):974\u0026ndash;1002\u003c/li\u003e\n \u003cli\u003eYaltırak C, Alpar B, Y\u0026uuml;ce H (2002) Tectonic elements controlling the evolution of the Gulf of Saros, NE Aegean Sea, T\u0026uuml;rkiye. \u003cem\u003eMar Geol\u003c/em\u003e 190(1\u0026ndash;2):261\u0026ndash;282. https://doi.org/10.1016/S0025-3227(02)00350-4\u003c/li\u003e\n \u003cli\u003eYıldırım C, Schildgen TF, Echtler H, Melnick D, Strecker MR (2011) Late Neogene and active orogenic uplift in the Central Pontides associated with the North Anatolian Fault: implications for the northern margin of the Central Anatolian Plateau, T\u0026uuml;rkiye. \u003cem\u003eTectonics\u003c/em\u003e 30(5):TC5005. https://doi.org/10.1029/2010TC002756\u003c/li\u003e\n \u003cli\u003eYıldırım C, Schildgen TF, Echtler H, Melnick D, Strecker MR et al (2013) Tectonic implications of fluvial incision and pediment deformation at the northern margin of the Central Anatolian Plateau based on multiple cosmogenic nuclides. \u003cem\u003eTectonics\u003c/em\u003e 32:1107\u0026ndash;1120. https://doi.org/10.1002/tect.20066\u003c/li\u003e\n \u003cli\u003eZonenshain LP, Le Pichon X (1986) Deep basins of the Black Sea and Caspian Sea as remnants of Mesozoic back-arc basins. \u003cem\u003eTectonophysics\u003c/em\u003e 123(1\u0026ndash;4):181\u0026ndash;211. https://doi.org/10.1016/0040-1951(86)90197-6\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Black Sea, Sinop Basin, Arkhangelsky Ridge, active faulting, negative flower structure","lastPublishedDoi":"10.21203/rs.3.rs-8779310/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8779310/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe southern margin of the Eastern Black Sea is commonly regarded as a region of low seismicity, largely because onshore and offshore fault mapping remains limited. However, focal mechanism solutions from the last century indicate active normal and strike-slip faulting in addition to thrust earthquakes, with the reveal pronounced seismic clustering offshore of the Sinop Basin near Samsun. To investigate the origin of this seismotectonic complexity, approximately 1,300 km of high-resolution multichannel seismic reflection profiles were acquired, processed, and interpreted together with multibeam bathymetric data.\u003c/p\u003e \u003cp\u003eThis analysis addresses the long-standing debate on whether the basin represents a young foreland basin or a graben-type structure, and evaluates the present-day activity of basin-bounding faults. Fault geometries and their seafloor morphological expressions, particularly negative flower structures-provide key constraints on the regional seismotectonic framework.\u003c/p\u003e \u003cp\u003eFour seismic units were identified and correlated with Upper Cretaceous\u0026ndash;Paleocene, Eocene, Oligo\u0026ndash;Miocene, and Plio\u0026ndash;Quaternary successions. Faults that terminate above the Upper Cretaceous\u0026ndash;Paleocene units are interpreted as inactive, whereas faults that cut all seismic units and reach the seafloor are considered active. Faults confined to the Plio\u0026ndash;Quaternary unit are interpreted as syn-sedimentary.\u003c/p\u003e \u003cp\u003eThese results indicate that the Sinop Basin is not a passive depression but an actively deforming basin controlled by oblique to strike-slip faulting. The mapped active faults are capable of generating earthquakes with magnitudes of Mw\u0026thinsp;\u0026asymp;\u0026thinsp;6.2\u0026ndash;6.9, implying a significant seismic hazard for the central Black Sea region.\u003c/p\u003e","manuscriptTitle":"Tectonic and Morphological Features of a Submarine Negative Flower Structure: In the Sinop Basin (Central Black Sea) and the Evaluation of Regional Seismic Hazard","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-11 08:19:06","doi":"10.21203/rs.3.rs-8779310/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e0b1ea43-5d1e-4544-9872-7fddd59ccb1e","owner":[],"postedDate":"February 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-11T10:21:34+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-11 08:19:06","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8779310","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8779310","identity":"rs-8779310","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}