Tectonic History of Diebold Knoll from Integration of Seismic, Gravity and Magnetic Data

Tectonic History of Diebold Knoll from Integration of Seismic, Gravity and Magnetic Data | 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 History of Diebold Knoll from Integration of Seismic, Gravity and Magnetic Data Md Ariful Islam, Irina Filina, Anne Tréhu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8689065/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 Subducting seamounts are thought to be a major factor affecting subduction zone processes, although details of their impact remain poorly understood. Incorporating seamounts into geodynamic models requires accurate knowledge of their density structure and tectonic history, but determining these parameters is challenging, especially when the seamounts are partially or completely buried by a thick sediment cover on the subducting plate. We focus on an intraplate seamount known as Diebold Knoll, which is evident in bathymetry approximately 60 km west of the Cascadia subduction zone deformation front. The objectives of this research are to determine the settings the Diebold Knoll was formed and to evaluate heterogeneities in the physical properties of oceanic crust resulting from its addition. We present an integrated geophysical analysis combining seismic reflection data, gravity, and magnetic anomalies along two intersecting profiles across the seamount. Our gravity analysis reveals that Diebold Knoll is not isostatically compensated and may have up to 1 km thick root. Our modeling suggests that the top ~ 1 km of the seamount exhibits lower values of density (2.6 g/cm³) and magnetic susceptibility (100 µcgs) relative to the adjacent crust, attributed to syn-formation faulting and post-formation hydration. The negative magnetic anomaly of the seamount and the stratigraphic relationships of the seamount complex and the hosting sedimentary layers, including the presence of a 0.9 Ma horizon, indicate that Diebold Knoll is considerably younger (4.5–0.9 Ma) than the underlying oceanic crust (7-7.5 Ma) and was formed in the intraplate settings. Seamounts seafloor topography Cascadia Subduction Zone Gravity model Magnetic model Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Chapter 1 Introduction: The Cascadia Subduction Zone (CSZ; Fig. 1 ) is characterized by arc volcanoes, a well-defined accretionary wedge, and a paleoseismic history of great megathrust earthquakes (Parsons et al., 2005 ; Schmalzle et al., 2014 ). However, compared to other subduction zones, the CSZ has much lower overall seismicity, as is described in the reviews by Trehu et al. ( 1994 ) and Walton et al. ( 2021 ). There are regions of relatively high seismicity in both subducting and overriding plates in the northern and southern parts of the CSZ (Fig. 1 ), whereas the central part (~ 43°N-47°N) is anomalously quiet (Han et al., 2018 ; Bodmer et al., 2018 ; Ashraf et al., 2025 ). This central part, however, hosts clusters of offshore earthquakes (M < 5) between 44.3°N and 44.7°N(Tréhu et al., 2015) that may result from interaction between subducted seamounts and the crystalline forearc basement (Tréhu et al., 2012). GPS data indicate that the JdF and North American plates are locked or partially locked along the CSZ (McCaffrey et al., 2007 ; Burgette et al., 2009 ; Schmalzle et al., 2014 ). While modern instrumental records show low seismicity along CSZ, historical records suggest the large megathrust events in the past, such as the one that caused tsunami waves in Japan that propagated across the Pacific Ocean on January 26th, 1700, A.D. (Satake et al., 2003 ; McCaffrey et al., 2013 ; Atwater et al., 2015 ). Abundant evidence of paleo-seismicity in the area suggests that great megathrust earthquakes occurred many times during the Holocene along the CSZ (Rogers, 1988 ; Goldfinger et al., 2012 ; Melgar, 2021 ). Significant earthquake events occur roughly every 220–550 years (Atwater and Hemphill-Haley, 1997 ; Goldfinger et al., 2017 ). A great megathrust earthquake of similar magnitude can also be expected in the future and poses a significant risk to the Pacific Northwest coastal regions (Rogers, 1988 ; Walton et al., 2021 ). According to some studies, seamounts on a subducting slab may increase the likelihood of large earthquakes by accumulating stress, causing plate locking and contributing to subduction zone segmentation and erosion of the crust of the overriding plate (Kodaira et al., 2000 ; Bilek et al., 2003 ; Singh et al., 2011 ). In contrast, other studies suggest that the subduction of seamounts can distribute stress over a wide region around the subducting feature by creating a fracture network in the overlying plate, which may lead to aseismic slip behavior (Wang and Bilek, 2011 ; 2014 ). In addition, seamounts influence the thermal structure of the incoming oceanic crust by modifying hydrothermal circulation, which in turn may affect the temperature and frictional properties of the plate boundary fault (Spinelli and Harris, 2011 ). Furthermore, the impact of a seamount on the subduction stress distribution may depend on the presence or absence of a crustal root, which affects the buoyancy of subducting slab. It is therefore important to know the crustal architecture, physical properties, age, and tectonic evolution of individual seamounts in order to model their potential impact on the subduction process. This study focuses on Diebold Knoll, a volcanic seamount complex on the Juan de Fuca plate, located ~ 60 km west of the deformation front of the CSZ. Diebold Knoll is an intraplate seamount with a relief of approximately 750 m from the surrounding seafloor (Fig. 1 ) and ~ 1400 m from the top of the Juan de Fuca (JdF) plate’s crust. Diebold Knoll is categorized as a "knoll" because its flat top is less than 1000 meters above the seafloor (Buchs et al., 2016). This seamount complex comprises four interconnected volcanic peaks, two of which are exposed above the seafloor sediments (as seen in the inset map in Fig. 1 ), the third is represented by a sediment-covered bump on the seafloor, and the fourth is deeply buried under a flat seafloor. The whole seamount complex is approximately 15 km long and 8 km wide. Using seismic and potential field data, we investigate the tectonic history of the Diebold Knoll and variations in crustal properties associated with its formation to evaluate the potential impact of similar structures that appear to have been subducted beneath the Cascadia subduction zone in the recent past (Fleming and Tréhu, 1999; Tréhu et al., 2012). Many buried and previously unrecognized seamounts on the JdF plate (including the buried parts of Diebold Knoll) have been discovered within a few tens of kilometers of the CSZ, as shown as stars in Fig. 1 , by recent geophysical surveys such as MGL2104 (Carbotte et al., 2022 ), RR1718 (Tominaga et al., 2018 ); MGL1211 (Han et al., 2016 ; Canales et al., 2017 ) and MGL1212 (Holbrook et al., 2012 ). These surveys were able to image the Moho beneath some of these seamounts. Lee et al. ( 2022 ) reported the presence of several seamounts along the CSZ from analysis of MGL2104 seismic reflection data. Except for the two seamounts in lines PD11/MCS03 (red stars on Fig. 1 ), all other seamounts from Lee et al. ( 2022 ) show no sign of a crustal root, i.e. are not isostatically compensated, implying that they are relatively young and were formed on lithosphere old enough to support the extra load (Watts et al., 2010 ). This study aims to provide a better understanding of an important geological feature on the subducting oceanic slab (the Diebold Knoll) that serves as an analog to seamounts that have already been subducted and may influence seismicity patterns. In this paper, we integrate various geophysical methods to achieve two main objectives. The first objective is to constrain the age of Diebold Knoll and the tectonic settings it was formed in (near-the-ridge vs. intraplate) from analysis of magnetic and seismic data. The second objective is to determine how the formation of the seamount altered the hosting oceanic crust. We model the physical properties, such as bulk density and magnetic susceptibility, of the seamount complex, and the hosting oceanic crust from gravity and magnetic anomalies. We also explore crustal architecture associated with the formation of the seamount, in particular, the presence or absence of a crustal root. These parameters impact the strength and buoyancy of the subducting plate. In particular, an older seamount may be isostatically adjusted and have a crustal root in contrast to a younger seamount. Depending on their formation settings, these features may behave differently during subduction due to differences in crustal strength and thickness. Chapter 2 Data and Methodology Geophysical Data We use a combination of geophysical datasets, each serving different purposes. For our integrated geophysical models, we used gravity (Fig. 2a) and magnetic anomalies (Fig. 2b), and seismic reflection data (Fig. 2c) for two crossing profiles (Lines 14 and 15 from the cruise RR1718; Tominaga et al., 2018 ). We also used published seismic refraction surveys (Tréhu et al., 1994; Horning et al., 2016 ; Canales et al., 2017 ) and the ocean drilling data (Kulm et al., 1973a ; Deep Sea Drilling Project, 1989 ) as constraints in analysis. Gravity anomalies We use two sets of gravity data. The first is marine gravity data from the cruise RR1718 (Tominaga, 2017a ). The second is global satellite gravity data from Sandwell et al. ( 2014 ). The use of regional data is necessary to extend modeled profiles along Lines 14 and 15 beyond the surveyed seismic lines to reduce the edge effects in the models. Merging the marine and satellite data into a continuous record is done before gravity modeling by assuming satellite data as a baseline, shifting the marine data to that baseline, and interpolating values at both ends (see details in Islam, 2023 ). Magnetic anomalies Magnetic anomaly data (total intensity after the ambient field was removed) were obtained from the North American magnetic anomaly grid (Bankey et al., 2002 ). We also incorporate a second set of magnetic anomaly data obtained from the cruise RR1718 (Tominaga, 2017b ). This data was collected simultaneously with marine gravity data using a SeaSpy magnetometer system. However, marine magnetic data were only recorded along Line 14. Line 15 was not surveyed due to a kink in its trajectory that prevented deploying the magnetometer, so it was modeled using the North American magnetic anomaly grid. The surveyed marine magnetic Line 14 is also shorter than the modeled profile 14, so we merge both magnetic datasets using the same procedure as for the gravity data. Seismic : The seismic images (Fig. 2c) are presented in Two-Way Travel Time (TWT) and were divided into three sections based on major layer boundaries: the water-seafloor and sediment-crust interfaces. To convert TWTT to depth, a constant acoustic velocity was assumed for the water layer (1480m/s – as it flattens the seafloor better; Telford et al., 1990 ). Velocity gradients were applied for different layers: from 1550 to 2300 m/s for abyssal plain sediments; from 1550–5500 m/s for sediments within the accretionary prism; and from 5500 to 7000 m/s for the crystalline crust (Deep Sea Drilling Project, 1989 ; Han et al., 2016 ; Horning et al., 2016 ). Methodology We develop integrated geophysical models along extended Lines 14 and 15 (Figs. 3 and 4). For these models, the subsurface is divided into several layers that include water, sediments (several layers), crust (upper and lower), and mantle. Each layer in the model is subdivided into several blocks, which are assigned physical properties (density and magnetic susceptibility) to compute the gravity and magnetic anomalies for the model. Three parameters, namely density, magnetic susceptibility, and layer geometry, can be adjusted to ensure that the calculated gravity and magnetic anomalies align with the observed potential fields. However, some of those parameters cannot be modified as they are constrained by geophysical data and scientific drilling results. Below is the list of constraints assumed for each subsurface layer: Water The water density value of 1.03 g/cm 3 and zero magnetic susceptibility are assigned (Telford et al., 1990 ). The thickness of the water column is determined from bathymetry data (Fig. 1 ) and is fixed during modeling. Sediments Sedimentary layers are assigned densities ranging from 2.0 g/cm 3 (top layer) to 2.65 g/cm 3 (bottom layer near the subduction zone) following similar studies in this area (Ashraf, 2021 ; Ashraf and Filina, 2023a ). These high densities at the bottom of the accretionary prism are consistent with seismic refraction results of Tréhu et al. (1994) and Canales et al. ( 2017 ) and are interpreted as evidence of compaction and diagenesis. A magnetic susceptibility of zero is assigned to all sediments. Oceanic crust We divide it into distinct upper and lower crustal units (oceanic layers II and III). This division enhances the accuracy of the models by accounting for significant variations in physical properties, especially density, between these layers (Carlson and Herrick, 1990). Density values of 2.65 g/cm 3 and 2.95 g/cm 3 for the upper and lower crust, respectively, were assigned, which are consistent with changes in P-wave crustal velocities of JdF (Tréhu et al., 1994; Gerdom et al., 2000 ; Horning et al., 2016 ; Canales et al., 2017 ). The magnetic susceptibility of the Juan de Fuca plate is not very well constrained. For instance, Horning et al. ( 2016 ) observed values ranging from 1,000 to 10,000 µcgs units in the upper crust, while Ashraf and Filina ( 2023b ) used a flat value of +/- 2000 µcgs with the sign relating to magnetic polarity. We assumed a single value (+/-1500 µcgs) for both the upper and lower crust due to limited published research differentiating magnetism between these layers. The chrons outlined in Fig. 1 were used to constrain the boundaries between the normal and reversely polarized blocks of the JdF crust. Mantle The mantle is assigned a density of 3.3 g/cm 3 and zero magnetic susceptibility (Telford et al., 1990 ). As Moho was not imaged by RR1718 data (Fig. 2c), the depth to Moho from adjacent seismic refraction experiments was extrapolated to the study area (Canales et al., 2017 ; Han et al., 2016 ). These studies suggest that the average thickness of the oceanic crust is ~ 6.5 km with ~ 2 km thick oceanic layer II (basalts) and ~ 4.5 km thick gabbroic layer (layer III). Once all the parameters have been assigned, GM-SYS (Geosoft Oasis Montaj, 2021), gravity and magnetic modelling extension of Geosoft Oasis Montaj was used to compute gravity and magnetic fields for this model, and model predictions were compared with observed data. Model parameters were then adjusted to improve the fit between the predictions and the observations. It must be noted here that not all parameters can be changed as many of them are constrained with drilling, bathymetry, seismic and/or laboratory measurements (such as thickness and physical properties of water, thickness and densities of sedimentary layer, as well as published densities and magnetic susceptibilities for oceanic basalts). In addition, physical properties of each layer can vary only within a geologically appropriate range. Moreover, the same values are used for the corresponding layers of both models. Therefore, at each iteration, a careful evaluation is performed of each model parameter to ensure that adjustment does not violate a priori constraint or geologic reasoning and remain consistent for both models. When a satisfactory match is achieved with geologically plausible parameters, the model is assumed to represent the true subsurface structures. Chapter 3 Results for different geological scenarios Several integrated models were developed for two modeled profiles (aligned with Lines 14 and 15) for three different geological scenarios. Scenario 1 Flat Moho beneath Diebold Knoll with no crustal bending This scenario assumes no root beneath the Diebold Knoll seamount complex and implies that the seamount is either very young (the root has not formed yet) or was added to exceptionally strong crust that does not bend due to this load, which in both cases indicates intraplate volcanism away from the spreading center. Both modeled profiles (Fig. 3 ) reveal important variations in physical properties within the seamount. Specifically, the uppermost part of the knoll, exposed to seawater, has a lower density of 2.6 g/cm 3 compared to the surrounding oceanic layer II with a density of 2.65 g/cm 3 . The choice of density value of 2.6 g/cm 3 for the top of the seamount complex (shown as a light pink color in Figs. 3 a and b) is justified during the sensitivity test shown in Fig. 3 c. Three different density values of 2.55, 2.60, and 2.65 g/cm 3 were evaluated for the topmost layer of the seamount complex in this gravity sensitivity test. Although all the values produced similar shapes of anomalies, the amplitude of computed anomaly for density value of 2.60 g/cm 3 resulted in the best match with the observed gravity field, suggesting a better gravity fit if the upper portion of the seamount is modeled with a lower density than the surrounding basaltic crustal layer. Additionally, this uppermost part of the knoll requires a significantly lower magnetic susceptibility of 100 µcgs compared to the surrounding upper crust with a magnetic susceptibility of 1500 µcgs to fit the observed magnetic field. Seismic velocity analysis of seismic reflection profiles from CASIE21 supports these lower density and magnetic susceptibility values determined from our modeling. Lee et al. ( 2022 ) reported a pronounced decrease in velocity gradient within the upper part of the seamount. Lower density, reduced magnetic susceptibility, and decreased seismic P-wave velocity are also observed by other studies in the CSZ (Watts et al., 2021 ; Lee et al., 2022 ; Ashraf et al., 2025 ). We interpret these to be the result of faulting and hydration of the Diebold Knoll during or after its formation. These processes are documented on the JdF plate and are attributed to the subduction-related crustal bending (Nedimović et al., 2009 ; Ashraf et al., 2025 ). Overall, this scenario provides a reasonable fit in that portion of the model that has seismic constraints (black arrow at the bottom of Figs. 3 a and 3 b). Scenario 2 Isostatically compensated seamount In this scenario, the seamount is assumed to be completely isostatically compensated. This implies that the seamount either had time to reach isostasy (i.e., relatively old), or it was added to a young and weak oceanic crust in the near-ridge settings. The root thickness is calculated using the Airy isostasy model (Airy, 1855 ; Telford et al., 1990 ), assuming physical properties derived in Scenario 1. This results in a 2.75 km thick root (Fig. 4a) and consequently about 10.5 mGal mismatch between calculated and observed gravity anomalies, while the magnetic anomaly is not much affected. To reconcile the gravity anomalies, this model requires an unusually high density (~ 3.0 g/cm 3 ) for the top of the seamount complex, which consequently impacts the thickness of its root. This creates a trade-off situation when either the observed gravity field is matched using anomalously high-density values for extrusive igneous rocks (which is not supported by existing literature), or a significant gravity anomaly mismatch arises due to a thick root in the model. We consider this scenario unlikely due to a significant gravity mismatch that can be removed only with geologically unrealistic density values for the seamount complex. Scenario 3 Crustal root thickness assigned based on analogous regional examples In this scenario, the root thickness beneath the Diebold Knoll is estimated based on the analysis of similar seamounts located on the Juan de Fuca plate and surveyed during two seismic cruises (Han et al., 2016 ; Carbotte et al., 2022 ). The first one is Seamount L1-SM04, which has a height of ~ 320 m above the basement and ~ 230 m thick root, estimated from interpreted seismic profiles from Han et al. ( 2016 ). The second is seamount PD11/MCS03 from Lee et al. ( 2022 ), which rises ~ 1.14 km above the crust, and the estimated root is up to 1 km thick. Notably, all other seamounts from Lee et al. ( 2022 ) show no sign of an isostatic root beneath the crust. For both “rooted” seamounts, the computed root-to-height ratio is 0.65. Since the Diebold Knoll is situated in similar tectonic settings as these two seamounts, this ratio was used to estimate the potential thickness of the root, resulting in 0.9 km (Fig. 4b). Since the crust bending in this case is not as pronounced as in the second scenario, the calculated gravity anomaly only exhibits up to ~ 3 mGal misfit when compared to the observed gravity field. Figure 4b illustrates this mismatch, which could potentially be improved by adjusting the Moho boundary within a 0.5 km range under the seamount complex or by adding density heterogeneities within the seamount complex (less than 0.05 g/cm 3 with respect to values used for Fig. 4b). The exact fit for this scenario can be achieved by multiple combinations of the above-mentioned factors. However, we intentionally kept the crustal structure and physical properties consistent with previous scenarios and did not attempt to achieve a complete fit between observed and computed gravity fields to illustrate uncertainties of the modeling. We consider that this scenario describes a thickest reasonable root beneath Diebold Seamount based on the gravity misfit. Chapter 4 Discussion Our study allows us to discriminate between two potential settings of the seamount formation. The Diebold Knoll may have formed in the near-ridge settings close to the Juan de Fuca spreading center, immediately after the oceanic crust was created, implying the seamount was emplaced onto young, weak crust (our Scenario 2). Alternatively, it could have formed far from the ridge in an intraplate setting, where it would be added to older, stronger crust (Scenarios 1 and 3). The lack of direct samples from Diebold Knoll complicates the determination of its precise age, but magnetic anomaly data and cross-cutting relationships of the seamount complex and sedimentary layers can provide some age constraints. Pronounced NNE-SSW trending highs and lows in magnetic anomalies, as shown in Fig. 2b, reflect magnetic reversals, with Diebold Knoll being associated with a strong negative anomaly, indicative of a reverse polarity during its formation. The crust beneath the knoll is estimated to be around 7 to 7.5 million years old (Figs. 1 and 2b), providing the oldest possible time of the knoll's emplacement after the formation of the hosting oceanic crust. There have been seven instances of magnetic reverse polarity since the formation of the crust in the vicinity of Diebold Knoll (Fig. 5 ), so magnetic anomaly data alone cannot resolve which of these periods corresponds to the seamount's formation. If Diebold Knoll formed near the spreading center, it would be added to a young and weak crust, and its age would likely be similar to that of the surrounding crust, with possible time ranges of formation in the late Miocene to early Pliocene (7–4.7 Ma). In this case, the seamount should develop a root, as was tested in our Scenario 2 (Fig. 4a). In contrast, if it formed far from the Juan de Fuca Ridge as part of intraplate volcanism, the seamount could have been emplaced during one of the four reverse polarity periods from the mid Pliocene to late Pleistocene (4.5–0.9 Ma). During this time the crust would have been relatively strong and stable to support the seamount without significant crustier flexure as described in our Scenario 1 (Fig. 3 ) and Scenario 3 (Fig. 4b). In those scenarios, we focus on the fact of the intraplate formation, and do not address the source and reasoning of the magmatic event responsible for the seamount development. We analyze the results from a nearby ocean drilling site and seismic reflection profiles to further constrain the age of Diebold Knoll (Fig. 6). DSDP-18 Site 174, located ~ 113 km north of Diebold Knoll, provides insights into the likely composition of sediments that lap onto Diebold Knoll, although it does not directly sample the oceanic crust. Site 174 penetrated a sedimentary sequence composed of two primary units (Fig. 6b). Unit 1 (0-284 mbsf) consists of medium to very fine turbidite sand layers, interpreted as deposits from the Astoria Fan, with sediment primarily originating from the Columbia River (Kulm et al., 1973b ; von Huene and Kulm, 1973 ; Prytulak et al., 2006 ). Unit 2 (284–879 mbsf) is an abyssal plain deposit consisting of Upper Pleistocene to Pliocene basal silt, grading upward to silty clay (Fig. 6). The boundary between these two units is pronounced on seismic profiles, and the seismic reflection data from MCS01P1 (Han et al., 2016 ) suggests that this boundary represents the distal edge of the current trench wedge. While age dating at Site 174 is insufficient to confirm whether this boundary represents a major depositional shift (Kulm et al., 1973a ), the seismic data provide valuable insights into the regional sedimentary context. Recent seismic studies (Shuck et al., 2023 ; Carbotte et al., 2024 ) provide a framework for estimating the age of the sediments that lap onto and partially bury Diebold Knoll. A composite seismic profile (Shuck et al., in prep), extending from Vancouver Island to the Oregon/California border, crosses the MCS01P1 line and ties to well-dated ODP data from Site 1027 (Rohr et al., 2019 ). The deepest horizon dated by Shuck et al. ( 2023 ) was estimated to have an age of 0.90 Ma and is observed throughout the region (Perrin et al., in prep). We translated the depth of this horizon from the depth section of Shuck et al. ( 2023 ) to time sections to link to Diebold Knoll and DSDP Site 174 to give the age model (See Figure S1 for details about tracking this link among different seismic profiles). Most of the sediment lapping onto the eastern flank of “Little Diebold” (an informal name for the buried seamount, imaged on Line 15 in Fig. 6d) corresponds to trench deposits formed since this time. This area of the Cascadia margin is characterized by thick trench deposits, interpreted to be the result of large mass transport events and related in situ deformation (Goldfinger et al., 2003 ; Tréhu et al., 2022). Correlating strata across Diebold Knoll, from seismic Line 15 to Line 14, remains challenging. A wedge of relatively incoherent strata represents an unconformable layer that overlies well-stratified sediments filling the basement highs (Fig. 6f, Unit 1). This wedge may represent either onlapping trench sediments, the southern edge of the Astoria Fan, or a combination of both (Perrin et al., in prep). The underlying, well-stratified sediments are interpreted as older deep ocean deposits similar to Unit 2 sampled at Site 174. These findings, combined with the regional basement topography, suggest that Diebold Knoll might have been extruded onto a rough basement, as evidenced by significant variations in the thickness of the strata that filled the basement low in the central part of Line 14 (Fig. 6f). Further east of "Little Diebold", onlapping sediments are predominantly trench deposits, including thick, internally incoherent layers interpreted as mass transport events younger than ~ 0.90 Ma (Tréhu et al., 2022). Some of these deposits appear to have overtopped a now-buried seamount, with disruption of the boundary between the two deposits indicating that the younger mass transport event may have scoured the seafloor, removing a thin layer of inter-event sedimentation. These deposits are absent in the shallow basin separating "Little Diebold" from Diebold Knoll (Tréhu et al., 2022). Together, the seismic data and the stratigraphic relationships suggest that Diebold Knoll formed in a geologically complex region, potentially involving multiple depositional and volcanic processes. While the precise timing of its emplacement remains uncertain, our integrated analysis, particularly the stratigraphic relationships with sediments older than 0.9 Ma and a lack of isostatic equilibrium suggested by our modeling, strongly supports an intraplate origin for Diebold Knoll. This implies that the seamount likely formed during a period of reverse magnetic polarity in the mid-Pliocene (4.5 Ma) to late Pleistocene (older than 0.9 Ma), consistent with emplacement on strong, mature lithosphere. Future studies, particularly those incorporating direct geological samples, will be critical to refining these age estimates and resolving the complex interactions between Diebold Knoll, the surrounding crust, and regional tectonic processes. Chapter 5 Conclusions This study integrates multiple geophysical datasets to construct a detailed model of the crustal architecture and physical properties of Diebold Knoll, which resides on ~ 7 Myr old oceanic Juan de Fuca lithosphere ~ 60 km to the west of the subduction front. We conclude that the uppermost portion of Diebold Knoll (~ 1 km above the basement) exhibits a lower density (2.6 g/cm³) and a significantly reduced magnetic susceptibility (100 µcgs) compared to the surrounding upper oceanic crust of the Juan de Fuca plate (2.655 g/cm³ and 1500 µcgs). These lower physical properties suggest faulting and hydration processes occurring during or after the formation of the seamount, consistent with recent seismic surveys reporting a reduced seismic velocity gradient in this region. The rest of the seamount complex has physical properties similar to surrounding oceanic crust, indicating it is primarily composed of materials with similar densities and magnetic susceptibilities. Our modeling suggests that Diebold Knoll is either located over a flat Moho or possesses a very thin (≤ 1 km) crustal root, suggesting it was emplaced in the intraplate settings and is not isostatically compensated. The seamount was added to the lithosphere, old enough to support the weight of the seamount without significant crustal deformation. The entire seamount complex is reversely magnetized, pointing to several potential time intervals for its formation: two in the Miocene, three in the Pliocene, and two in the Quaternary. Recent work by Shuck et al. ( 2023 ) and Carbotte et al. ( 2024 ) offers valuable stratigraphic correlations of ocean drilling data with regional seismic profiles in CSZ that may help refine these age estimates. Incorporating the results of their analysis suggests that the seamount's emplacement could have occurred as recently as the late Pliocene to late Pleistocene (4.5–0.9 Ma). The physical property variations within Diebold Knoll and its complex stratigraphic relationships offer key constraints for understanding the geologic evolution of the Cascadia subduction zone (CSZ). These findings contribute to our understanding of seamount formation, its interactions with the surrounding crust, and its potential role in subduction zone dynamics. Moreover, the integrated approach used here, combining seismic data, magnetic properties, and stratigraphic correlations, provides a framework for studying crustal structure, physical property heterogeneities, and the age of formation in other regions hosting intraplate seamounts. Declarations Competing interests: The authors acknowledge that there are no conflicts of interest recorded. Ethical approval: Not applicable. Author Contribution M.A.I. and I.F. contributed to the conceptualization of the study. M.A.I. performed most of the data analysis and led the investigation and manuscript writing. I.F. and A.M.T. provided supervision and contributed to manuscript editing and revisions. A.M.T. contributed to figure preparation. All authors reviewed and approved the final manuscript. Acknowledgments: This research was supported by the Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln. Data availability: All the data that support the findings of this study are open access. Please see the relevant citations for the data URL. References Airy GB (1855) On the computation of the effect of the attraction of mountain-masses, as disturbing the apparent astronomical latitude of stations in geodetic surveys: Philosophical Transactions of the Royal Society of London, v. 145. 101–104. 10.1098/RSTL.1855.0003 Ashraf A (2021) Geological Structures and Crustal Architecture of the Cascadia Subduction Zone from the Integration of Multiple Geophysical Datasets: University of Nebraska-Lincoln, doi: https://digitalcommons.unl.edu/geoscidiss/135 Ashraf A, Filina I (2023a) New 2.75-D gravity modeling reveals the low-density nature of propagator wakes in the Juan de Fuca plate: Tectonophysics, v. 869. 230127. 10.1016/j.tecto.2023.230127 Ashraf A, Filina I (2023b) Zones of Weakness Within the Juan de Fuca Plate Mapped From the Integration of Multiple Geophysical Data and Their Relation to Observed Seismicity: Geochemistry, Geophysics, Geosystems, v. 24. 10.1029/2023GC010943 Ashraf A, Hooft EEE, Toomey DR, Tréhu AM, Nolan S, Wirth EA, Ward KM (2025) A High-Resolution 3-DP-Wave Velocity Structure of the South-Central Cascadia Subduction Zone From Wide-Angle Shore-Crossing Seismic Refraction Data: Journal of Geophysical Research: Solid Earth, v. 130, p. e2024JB029525 Atwater BF, Hemphill-Haley E (1997) Recurrence intervals for great earthquakes of the past 3,500 years at northeastern Willapa Bay. Professional Paper, Washington. 10.3133/PP1576 Atwater BF, Musumi-Rokkaku S, Satake K, Tsuji Y, Ueda K, Yamaguchi DK (2015) The orphan tsunami of 1700—Japanese clues to a parent earthquake in North America:, https://doi.org/10.3133/pp1707 Bankey V et al (2002) Digital data grids for the magnetic anomaly map of North America: Open-File Report. 10.3133/OFR02414 Bilek SL, Schwartz SY, DeShon HR (2003) Control of seafloor roughness on earthquake rupture behavior: Geology, v. 31. 455–458. 10.1130/0091-7613(2003)031%3C0455:COSROE%3E2.0.CO;2 Bodmer M, Toomey DR, Hooft EEE, Schmandt B (2018) Buoyant Asthenosphere Beneath Cascadia Influences Megathrust Segmentation: Geophysical Research Letters, v. 45. 6954–6962. 10.1029/2018GL078700 Burgette RJ, Weldon RJ, Schmidt DA (2009) Interseismic uplift rates for western Oregon and along-strike variation in locking on the Cascadia subduction zone. J Geophys Research: Solid Earth v 114. 10.1029/2008JB005679 Canales JP, Carbotte SM, Nedimovic MR, Carton H (2017) Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone: Nature Geoscience, v. 10. 864–870. 10.1038/NGEO3050 Carbotte SM et al (2024) Subducting plate structure and megathrust morphology from deep seismic imaging linked to earthquake rupture segmentation at Cascadia. Sci Adv v 10. 10.1126/sciadv.adl3198 Carbotte S, Boston B, Han S (2022) Multi-Channel Seismic Shot Data from the Cascadia margin acquired during Langseth cruise MGL2104 (2021): IDEA Project DSD (1989) Archive of Core and Site/Hole Data and Photographs from the Deep Sea Drilling Project (DSDP): National Geophysical Data Center, NOAA, doi: 10.7289/V54M92G2 Fleming SW, Trehu AM (1999) Crustal structure beneath the central Oregon convergent margin from potential-field modeling: Evidence for a buried basement ridge in local contact with a seaward dipping Gerdom M, Trehu AM, Flueh ER, Klaeschen D (2000) The continental margin off Oregon from seismic investigations: Tectonophysics, v. 329. 79–97. 10.1016/S0040-1951(00)00190-6 Goldfinger C et al (2012) Turbidite event history—Methods and implications for Holocene paleoseismicity of the Cascadia subduction zone: Professional Paper. 10.3133/PP1661F Goldfinger C, Galer S, Beeson J, Hamilton T, Black B, Romsos C, Patton J, Nelson CH, Hausmann R, Morey A (2017) The importance of site selection, sediment supply, and hydrodynamics: A case study of submarine paleoseismology on the northern Cascadia margin, Washington USA: Marine Geology, v. 384. 4–46. 10.1016/j.margeo.2016.06.008 Goldfinger C, Nelson CH, Johnson JE (2003) Holocene Earthquake Records from the Cascadia Subduction Zone and Northern San Andreas Fault Based on Precise Dating of Offshore Turbidites: Annual Review of Earth and Planetary Sciences, v. 31. 555–577. 10.1146/annurev.earth.31.100901.141246 Han S, Carbotte SM, Canales JP, Nedimović MR, Carton H (2018) Along-Trench Structural Variations of the Subducting Juan de Fuca Plate From Multichannel Seismic Reflection Imaging. J Geophys Research: Solid Earth v 123:3122–3146. 10.1002/2017JB015059 Han S, Carbotte SM, Canales JP, Nedimovic MR, Carton H, Gibson JC, Horning GW (2016) Seismic reflection imaging of the Juan de Fuca plate from ridge to trench: New constraints on the distribution of faulting and evolution of the crust prior to subduction. J Geophys Research: Solid Earth v 121:1849–1872. 10.1002/2015JB012416 Holbrook WS, Kent G, Keranen K, Johnson HP, Trehu A, Tobin H, Caplan-Auerbach J, Beeson J (2012) Cascadia fore arc seismic survey: Open-access data available: Eos, Transactions American Geophysical Union, v. 93. 521–522. 10.1029/2012EO500002 Horning G, Canales JP, Carbotte SM, Han S, Carton H, Nedimović MR, van Keken PE (2016) A 2-D tomographic model of the Juan de Fuca plate from accretion at axial seamount to subduction at the Cascadia margin from an active source ocean bottom seismometer survey. J Geophys Research: Solid Earth v 121:5859–5879. 10.1002/2016JB013228 von Huene R, Kulm LD (1973) Tectonic Summary of Leg 18, in Initial Reports of the Deep Sea Drilling Project, 18, U.S. Government Printing Office. 10.2973/dsdp.proc.18.133.1973 Islam MA, Crustal structures of Diebold Knoll and adjacent Juan De Fuca oceanic crust from integration of seismic, gravity and magnetic data: University of Nebraska-, Lincoln (2023) https://digitalcommons.unl.edu/geoscidiss/151/ (accessed August 2023) Kodaira S, Takahashi N, Nakanishi A, Miura S, Kaneda Y (2000) Subducted Seamount Imaged in the Rupture Zone of the 1946 Nankaido Earthquake: Science, v. 289. 104–106. 10.1126/SCIENCE.289.5476.104 Kulm LD et al (1973a) Site 174, in Initial Reports of the Deep Sea Drilling Project, 18, U.S. Government Printing Office. 10.2973/dsdp.proc.18.105.1973 Kulm LD, Prince RA, Snavely PD (1973b) Site Survey of the Northern Oregon Continental Margin and Astoria Fan, in Initial Reports of the Deep Sea Drilling Project, 18, U.S. Government Printing Office. 10.2973/dsdp.proc.18.app1a.1973 Lee M, Carbotte SM, Shuck B, Han S, Boston B, Lee M, Carbotte SM, Shuck B, Han S, Boston B (2022) Examining sediment consolidation state and hydrothermal circulation at and near buried seamounts on the Cascadia Margin and its relation to earthquake generation: AGUFM, v. 2022, p. T42D-0147. https://ui.adsabs.harvard.edu/abs/2022AGUFM.T42D0147L/abstract (accessed May 2023) McCaffrey R, King RW, Payne SJ, Lancaster M (2013) Active tectonics of northwestern U.S. inferred from GPS-derived surface velocities. J Geophys Research: Solid Earth v 118:709–723. 10.1029/2012JB009473 McCaffrey R, Qamar AI, King RW, Wells R, Khazaradze G, Williams CA, Stevens CW, Vollick JJ, Zwick PC (2007) Fault locking, block rotation and crustal deformation in the Pacific Northwest. Geophys J Int v 169:1315–1340. 10.1111/j.1365-246X.2007.03371.x Melgar D (2021) Was the January 26th, 1700 Cascadia Earthquake Part of a Rupture Sequence? Journal of Geophysical Research: Solid Earth, v. 126, p. e2021JB021822. 10.1029/2021JB021822 Nedimović MR, Bohnenstiehl DWR, Carbotte SM, Pablo Canales J, Dziak RP (2009) Faulting and hydration of the Juan de Fuca plate system: Earth and Planetary Science Letters, v. 284. 94–102. 10.1016/j.epsl.2009.04.013 Norvell B, Kyritz T, Spinelli GA, Harris RN, Dickerson K, Tréhu AM, Carbotte S, Han S, Boston B, Lee M (2023) Thermally Significant Fluid Seepage Through Thick Sediment on the Juan de Fuca Plate Entering the Cascadia Subduction Zone: Geochemistry, Geophysics, Geosystems, v. 24, 10.1029/2023GC010868 Parsons T et al (2005) Crustal Structure of the Cascadia Fore Arc of Washington:, http://pubs.usgs.gov/pp/pp1661-D Prytulak J, Vervoort JD, Plank T, Yu C (2006) Astoria Fan sediments, DSDP site 174, Cascadia Basin: Hf–Nd–Pb constraints on provenance and outburst flooding: Chemical Geology, v. 233. 276–292. 10.1016/J.CHEMGEO.2006.03.009 Rogers GC (1988) An assessment of the megathrust earthquake potential of the Cascadia subduction zone 1:, https://doi.org/10.1139/e88-083 Rohr KMM, King H, Riedel M, Schmidt U (2019) From mid-plate to subduction zone: stratigraphy of the northeast Juan de Fuca Plate. offshore Br Columbia. 10.4095/314906 Ryan WBF et al (2009) Global multi-resolution topography synthesis: Geochemistry, Geophysics. Geosyst v 10. 10.1029/2008GC002332 Sandwell DT, Müller RD, Smith WHF, Garcia E, Francis R (2014) New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure: Science, v. 346. 65–67. 10.1126/SCIENCE.1258213 Satake K, Wang K, Geophysical BA-J, of (2003) and undefined, 2003, Fault slip and seismic moment of the 1700 Cascadia earthquake inferred from Japanese tsunami descriptions: Wiley Online Library, v. 108, p. 2535. 10.1029/2003JB002521 Schmalzle GM, McCaffrey R, Creager KC (2014) Central Cascadia subduction zone creep: Geochemistry, Geophysics, Geosystems, v. 15. 1515–1532. 10.1002/2013GC005172 Shuck B, Babendreier C, Han S, Carbotte SM, Beeson JW, Boston B, Tobin HJ, Lee M (2023) A New Regional Stratigraphic Framework for the Cascadia Oceanic Basin, in AGU Fall Meeting Abstracts, v. 2023, p. T53E–0197 Singh SC et al (2011) Aseismic zone and earthquake segmentation associated with a deep subducted seamount inSumatra: Nature Geoscience, v. 4. 308–311. 10.1038/ngeo1119 Spinelli GA, Harris RN (2011) Thermal effects of hydrothermal circulation and seamount subduction: Temperatures in the Nankai Trough Seismogenic Zone Experiment transect, Japan: Geochemistry, Geophysics, Geosystems, v. 12, p. n/a-n/a. 10.1029/2011GC003727 Telford WM, Geldart LP, Sheriff RE (1990) Appl Geophysics: Appl Geophys. 10.1017/CBO9781139167932 Tominaga M (2017a) Gravimeter (Bell BGM-3) data as collected during the cruise RR1718, Collaborative EAGER project: Early Career Seismic Chief Scientist Training Cruise. Rolling Deck to Repository (R2R). 10.7284/128301 Tominaga M (2017b) Magnetometer (MarineMagnetics SeaSPY) data as collected during the cruise RR1718, Collaborative EAGER project: Early Career Seismic Chief Scientist Training Cruise. Rolling Deck to Repository (R2R). 10.7284/128302 Tominaga M, Trehu A, Lyle M (2018) Multi-Channel Seismic Shot Data from the Seismic Early Career Chief Scientist Training Cruise 2017, Cascadia Margin, acquired during R/V Roger Revelle expedition RR1718 (2017). IEDA:, 10.1594/IEDA/324504 Trehu AM, Asudeh I, Brocher TM, Luetgert JH, Mooney WD, Nabelek JL, Nakamura Y (1994) Crustal Architecture of the Cascadia Forearc: Science, v. 266, pp. 237–243, 10.1126/SCIENCE.266.5183.237 Trehu AM, Blakely RJ, Williams MC (2012) Subducted seamounts and recent earthquakes beneath the central cascadia forearc: Geology, v. 40. 103–106. 10.1130/G32460.1 Trehu AM, Braunmiller J, Davis E (2015) Seismicity of the Central Cascadia Continental Margin near 44.5 N: A Decadal View: Seismological Research Letters, v. 86. 819–829. 10.1785/0220140207 Trehu AM, Tominaga M, Lyle M, Davenport K, Phrampus BJ, Favorito J, Zhang E, Lenz BL, Shreedharan S, Yelisetti S (2022) The Hidden History of the South-Central Cascadia Subduction Zone Recorded on the Juan de Fuca Plate Offshore Southwest Oregon: Geochemistry, Geophysics, Geosystems, v. 23, 10.1029/2021GC010318 Walker JD, Geissman JW (2022) Geologic Time Scale v. 6.0 - The Geological Society of America:, https://doi.org/10.1130/2022.CTS006C Walton MAL et al (2021) Toward an Integrative Geological and Geophysical View of Cascadia Subduction Zone Earthquakes: Annual Review of Earth and Planetary Sciences, v. 49. 367–398. 10.1146/annurev-earth-071620-065605 Wang K, Bilek SL (2011) Do subducting seamounts generate or stop large earthquakes? Geology, v. 39. 819–822. 10.1130/G31856.1 Wang K, Bilek SL (2014) Invited review paper: Fault creep caused by subduction of rough seafloor relief: Tectonophysics, v. 610. 1–24. 10.1016/J.TECTO.2013.11.024 Watts AB, Grevemeyer I, Shillington DJ, Dunn RA, Boston B, de la Gómez L (2021) Seismic Structure, Gravity Anomalies and Flexure Along the Emperor Seamount Chain: Journal of Geophysical Research: Solid Earth, v. 126, p. e2020JB021109. 10.1029/2020JB021109 Watts AB, Koppers AAP, Robinson DP (2010) Seamount Subduction and Earthquakes: Source: Oceanography, v. 23. 166–173. 10.2307/24861080 Wilson DS (1988) Tectonic history of the Juan de Fuca Ridge over the last 40 million years. J Geophys Res v 93. 10.1029/jb093ib10p11863 Wilson DS (2002) The Juan de Fuca plate and slab: isochron structure and Cenozoic plate motions:, 10.4095/222387 Additional Declarations No competing interests reported. Supplementary Files SupplementaryMaterialIslametal.docx 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-8689065","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":583710791,"identity":"f481b384-302e-4048-bc7d-8f09fd4325a8","order_by":0,"name":"Md Ariful Islam","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsklEQVRIiWNgGAWjYFCCBIYDDAUMDPzMIA4b0VoMGBgkm0nRwgDSYnCAWC267ckPD/4wsIs2Ps5jwPCh7DBhLWZnnhkc5jFIzt0GJBlnnCNGy40Eg8MMBsxgLcy8bURpSf8AdFh97uZmoJa/xGnJMTjAY3A4dwMzUAsjUVrOvCkAOul47ozDbAUHe86lE6HlePrmjz8qqnP7+w9vfPCjzJqwFhRwgET1o2AUjIJRMApwAQDhuD31XdW0LQAAAABJRU5ErkJggg==","orcid":"","institution":"University of Nebraska–Lincoln","correspondingAuthor":true,"prefix":"","firstName":"Md","middleName":"Ariful","lastName":"Islam","suffix":""},{"id":583710792,"identity":"cefa674e-ac23-4926-aafc-3d18e8f1184b","order_by":1,"name":"Irina Filina","email":"","orcid":"","institution":"University of Nebraska–Lincoln","correspondingAuthor":false,"prefix":"","firstName":"Irina","middleName":"","lastName":"Filina","suffix":""},{"id":583710793,"identity":"1c176a38-d1ba-4d66-81f9-55873fe4e203","order_by":2,"name":"Anne Tréhu","email":"","orcid":"","institution":"Oregon State University","correspondingAuthor":false,"prefix":"","firstName":"Anne","middleName":"","lastName":"Tréhu","suffix":""}],"badges":[],"createdAt":"2026-01-24 20:53:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8689065/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8689065/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101758862,"identity":"5ba216c2-a631-49df-9aef-f9aef35feccd","added_by":"auto","created_at":"2026-02-03 11:09:04","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":536946,"visible":true,"origin":"","legend":"\u003cp\u003eRegional map of the CSZ with the eastern boundary marked by the deformation front (dashed black and white line). Key tectonic elements are shown over a shaded bathymetry grid from GeoMapApp based on GMRT 4 (Ryan et al., 2009). Magnetic isochrons are adopted from Wilson (2002). Gray shaded area outlines the propagator wakes (Wilson, 1988; 2002) known to be weak zones of the JdF crust (Ashraf and Filina, 2023b). \u0026nbsp;Circles of different colors show locations of earthquakes with magnitude 4.0 and above recorded from 1918 to 2022 from the USGS earthquake catalog; focal depth of earthquakes is indicated by color, and magnitude by sizes of circles. The inset map shows a zoomed-in view of the Diebold Knoll. Stars are seamounts identified from different sources (indications of different colors are at the bottom of the figure; see text for details).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/c5fb689642d03b30788ed0f4.png"},{"id":101758751,"identity":"159505c8-03eb-460f-b284-5d654e59f6e4","added_by":"auto","created_at":"2026-02-03 11:08:27","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":632831,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 2. \u003c/strong\u003e(a) Regional Free-air gravity anomaly grid from Sandwell et al. (2014). Seismic reflection Lines 14 and 15 are from RR171 survey (Tominaga et al., 2018).\u003c/p\u003e\n\u003cp\u003e(b) Magnetic anomaly around the Diebold Knoll from Bankey et al. (2002) along with the location of 2D profiles in grey lines.\u003c/p\u003e\n\u003cp\u003e(c) Seismic reflection Lines 14 \u0026amp; 15 from RR1718 survey as viewed in OpendTect. Basement can be seen dipping toward the subduction zone on Line 15, while Moho is not imaged on either line.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/f799ea81665fa369bdcad6a9.png"},{"id":101758866,"identity":"2d0ea94b-9f39-4981-ba50-e2dd5405f102","added_by":"auto","created_at":"2026-02-03 11:09:06","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":130896,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Integrated geophysical model for scenario 1 (Flat Moho beneath the Diebold Knoll) for Line 15. The top panel is a plain view at 5 km depth. The numbers are densities and magnetic susceptibilities of different layers. Negative magnetic susceptibilities refer to reversely magnetized crustal rocks. Dashed rectangle shows the portion of the model used for sensitivity test provided in panel c.\u003c/p\u003e\n\u003cp\u003e(b) The same scenario for Line 14. Please note that all corresponding layers have the same physical properties.\u003c/p\u003e\n\u003cp\u003e(c) The sensitivity test for calculated gravity anomaly using different densities for the top block of the seamount (light pink layer). The value of 2.60 g/cm\u003csup\u003e3\u003c/sup\u003e represented by the blue line has the best-matching amplitude among all other tested density values.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/b057b83bfa7f1455e1defc30.png"},{"id":101758690,"identity":"3763bf94-b179-4103-b4f8-d089d8e2a91e","added_by":"auto","created_at":"2026-02-03 11:08:13","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":144946,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Integrated geophysical model for Scenario 2 (isostatically compensated Diebold Knoll) for Line 15. Note the large up to 10.5 mGal mismatch in gravity data. The geometries and physical properties of sediments are the same as in Figure 3. Note that the base of the accretionary prism is not well imaged in seismic data (Figure 2c), so no attempt to obtain a better match was done over that are due to lack of geometric constraints. (b) Scenario 3 (not completely compensated seamount) for the same line. The thickness of the root was estimated based on analog seamounts in the area.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/a11185c9d8325a2a74998b04.png"},{"id":101757542,"identity":"57ddaebf-2d22-4186-997d-ce0717cdec07","added_by":"auto","created_at":"2026-02-03 11:03:38","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":39003,"visible":true,"origin":"","legend":"\u003cp\u003eGeologic time scale adopted from Walker and Geissman (2022). Seven time-windows of negative magnetic polarities after the hosting oceanic crust was formed ~ 7 Ma.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/3b05781747482e268866e78b.png"},{"id":101757911,"identity":"adf06574-9c28-44a9-83ad-168aad47e2a0","added_by":"auto","created_at":"2026-02-03 11:05:08","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":413449,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Map of the study area showing locations of DSDP Site-174 and seismic lines shown in this figure. Note that exact location of vintage lines in panels (b) and (c) is not provided in the original publication, so their estimated locations are reported. Line 14 and 15 from RR1718.\u003c/p\u003e\n\u003cp\u003e(b) Seismic profile over DSDP-18 Site 174 adopted from Kulm et al. (1973). Unit 1 is more or less horizontal and interpreted as Astoria Fan sediments, whereas parallel reflectors in Unit 2 are inclined toward the subduction zone and are interpreted as abyssal plain sediments. This contact was encountered at depth 284 m below seafloor in the Site 174.\u003c/p\u003e\n\u003cp\u003e(c) West-East seismic profile ~30 km south of the DSDP-18 site 174. Units 1 and 2 in this profile were not interpreted in the original publication; they were projected from the drill site seismic image (Fig. 6b).\u003c/p\u003e\n\u003cp\u003e(d) Seismic Line 15 with interpreted sedimentary layers and acoustic basement. The red rectangle shows the extend of panel e.\u003c/p\u003e\n\u003cp\u003e(e) Seismic units projected from the DSPP site 174 located ~ 113 km to the north of the Diebold Knoll. The two sub-units are interpreted within each unit, namely two blue-colored ones for Unit 1 (abyssal plain sediments) and orange and yellow ones for Unit 2 (Astoria Fan deposits).\u003c/p\u003e\n\u003cp\u003e(f) Seismic line 15 with sedimentary deposit NW to the Diebold Knoll. The red box outlines the extent of panel f.\u003c/p\u003e\n\u003cp\u003e(g) Zoomed in portion of line 14. Sedimentary sequences of Unit 2 and the lower portion of Unit 1 are lapping onto the seamount suggesting that they were deposited before the Diebold Knoll.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/f33a7a94957eff7950941763.png"},{"id":104403558,"identity":"8b76316c-603a-4c95-bd25-8bd7c10c64f9","added_by":"auto","created_at":"2026-03-11 12:18:34","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2383578,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/82721059-0f4e-4935-a9b6-514eeb17f3d3.pdf"},{"id":101758968,"identity":"9eeffadf-a574-416d-9f60-6a96615c4386","added_by":"auto","created_at":"2026-02-03 11:09:28","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":6346354,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterialIslametal.docx","url":"https://assets-eu.researchsquare.com/files/rs-8689065/v1/cfdc294c619c4d0b08ee6617.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Tectonic History of Diebold Knoll from Integration of Seismic, Gravity and Magnetic Data","fulltext":[{"header":"Chapter 1 Introduction:","content":"\u003cp\u003eThe Cascadia Subduction Zone (CSZ; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) is characterized by arc volcanoes, a well-defined accretionary wedge, and a paleoseismic history of great megathrust earthquakes (Parsons et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Schmalzle et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, compared to other subduction zones, the CSZ has much lower overall seismicity, as is described in the reviews by Trehu et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e1994\u003c/span\u003e) and Walton et al. (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). There are regions of relatively high seismicity in both subducting and overriding plates in the northern and southern parts of the CSZ (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), whereas the central part (~\u0026thinsp;43\u0026deg;N-47\u0026deg;N) is anomalously quiet (Han et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Bodmer et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Ashraf et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). This central part, however, hosts clusters of offshore earthquakes (M\u0026thinsp;\u0026lt;\u0026thinsp;5) between 44.3\u0026deg;N and 44.7\u0026deg;N(Tr\u0026eacute;hu et al., 2015) that may result from interaction between subducted seamounts and the crystalline forearc basement (Tr\u0026eacute;hu et al., 2012). GPS data indicate that the JdF and North American plates are locked or partially locked along the CSZ (McCaffrey et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Burgette et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Schmalzle et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). While modern instrumental records show low seismicity along CSZ, historical records suggest the large megathrust events in the past, such as the one that caused tsunami waves in Japan that propagated across the Pacific Ocean on January 26th, 1700, A.D. (Satake et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; McCaffrey et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Atwater et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Abundant evidence of paleo-seismicity in the area suggests that great megathrust earthquakes occurred many times during the Holocene along the CSZ (Rogers, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Goldfinger et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Melgar, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Significant earthquake events occur roughly every 220\u0026ndash;550 years (Atwater and Hemphill-Haley, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Goldfinger et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). A great megathrust earthquake of similar magnitude can also be expected in the future and poses a significant risk to the Pacific Northwest coastal regions (Rogers, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Walton et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAccording to some studies, seamounts on a subducting slab may increase the likelihood of large earthquakes by accumulating stress, causing plate locking and contributing to subduction zone segmentation and erosion of the crust of the overriding plate (Kodaira et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Bilek et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Singh et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In contrast, other studies suggest that the subduction of seamounts can distribute stress over a wide region around the subducting feature by creating a fracture network in the overlying plate, which may lead to aseismic slip behavior (Wang and Bilek, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In addition, seamounts influence the thermal structure of the incoming oceanic crust by modifying hydrothermal circulation, which in turn may affect the temperature and frictional properties of the plate boundary fault (Spinelli and Harris, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Furthermore, the impact of a seamount on the subduction stress distribution may depend on the presence or absence of a crustal root, which affects the buoyancy of subducting slab. It is therefore important to know the crustal architecture, physical properties, age, and tectonic evolution of individual seamounts in order to model their potential impact on the subduction process. This study focuses on Diebold Knoll, a volcanic seamount complex on the Juan de Fuca plate, located\u0026thinsp;~\u0026thinsp;60 km west of the deformation front of the CSZ. Diebold Knoll is an intraplate seamount with a relief of approximately 750 m from the surrounding seafloor (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and ~\u0026thinsp;1400 m from the top of the Juan de Fuca (JdF) plate\u0026rsquo;s crust. Diebold Knoll is categorized as a \"knoll\" because its flat top is less than 1000 meters above the seafloor (Buchs et al., 2016). This seamount complex comprises four interconnected volcanic peaks, two of which are exposed above the seafloor sediments (as seen in the inset map in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the third is represented by a sediment-covered bump on the seafloor, and the fourth is deeply buried under a flat seafloor. The whole seamount complex is approximately 15 km long and 8 km wide. Using seismic and potential field data, we investigate the tectonic history of the Diebold Knoll and variations in crustal properties associated with its formation to evaluate the potential impact of similar structures that appear to have been subducted beneath the Cascadia subduction zone in the recent past (Fleming and Tr\u0026eacute;hu, 1999; Tr\u0026eacute;hu et al., 2012).\u003c/p\u003e \u003cp\u003eMany buried and previously unrecognized seamounts on the JdF plate (including the buried parts of Diebold Knoll) have been discovered within a few tens of kilometers of the CSZ, as shown as stars in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, by recent geophysical surveys such as MGL2104 (Carbotte et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), RR1718 (Tominaga et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2018\u003c/span\u003e); MGL1211 (Han et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Canales et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and MGL1212 (Holbrook et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). These surveys were able to image the Moho beneath some of these seamounts. Lee et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) reported the presence of several seamounts along the CSZ from analysis of MGL2104 seismic reflection data. Except for the two seamounts in lines PD11/MCS03 (red stars on Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), all other seamounts from Lee et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) show no sign of a crustal root, i.e. are not isostatically compensated, implying that they are relatively young and were formed on lithosphere old enough to support the extra load (Watts et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). This study aims to provide a better understanding of an important geological feature on the subducting oceanic slab (the Diebold Knoll) that serves as an analog to seamounts that have already been subducted and may influence seismicity patterns. In this paper, we integrate various geophysical methods to achieve two main objectives. The first objective is to constrain the age of Diebold Knoll and the tectonic settings it was formed in (near-the-ridge vs. intraplate) from analysis of magnetic and seismic data. The second objective is to determine how the formation of the seamount altered the hosting oceanic crust. We model the physical properties, such as bulk density and magnetic susceptibility, of the seamount complex, and the hosting oceanic crust from gravity and magnetic anomalies. We also explore crustal architecture associated with the formation of the seamount, in particular, the presence or absence of a crustal root. These parameters impact the strength and buoyancy of the subducting plate. In particular, an older seamount may be isostatically adjusted and have a crustal root in contrast to a younger seamount. Depending on their formation settings, these features may behave differently during subduction due to differences in crustal strength and thickness.\u003c/p\u003e"},{"header":"Chapter 2 Data and Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eGeophysical Data\u003c/h2\u003e \u003cp\u003eWe use a combination of geophysical datasets, each serving different purposes. For our integrated geophysical models, we used gravity (Fig.\u0026nbsp;2a) and magnetic anomalies (Fig.\u0026nbsp;2b), and seismic reflection data (Fig.\u0026nbsp;2c) for two crossing profiles (Lines 14 and 15 from the cruise RR1718; Tominaga et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). We also used published seismic refraction surveys (Tr\u0026eacute;hu et al., 1994; Horning et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Canales et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and the ocean drilling data (Kulm et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1973a\u003c/span\u003e; Deep Sea Drilling Project, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1989\u003c/span\u003e) as constraints in analysis.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eGravity anomalies\u003c/strong\u003e \u003cp\u003eWe use two sets of gravity data. The first is marine gravity data from the cruise RR1718 (Tominaga, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2017a\u003c/span\u003e). The second is global satellite gravity data from Sandwell et al. (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The use of regional data is necessary to extend modeled profiles along Lines 14 and 15 beyond the surveyed seismic lines to reduce the edge effects in the models. Merging the marine and satellite data into a continuous record is done before gravity modeling by assuming satellite data as a baseline, shifting the marine data to that baseline, and interpolating values at both ends (see details in Islam, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eMagnetic anomalies\u003c/strong\u003e \u003cp\u003eMagnetic anomaly data (total intensity after the ambient field was removed) were obtained from the North American magnetic anomaly grid (Bankey et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). We also incorporate a second set of magnetic anomaly data obtained from the cruise RR1718 (Tominaga, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2017b\u003c/span\u003e). This data was collected simultaneously with marine gravity data using a SeaSpy magnetometer system. However, marine magnetic data were only recorded along Line 14. Line 15 was not surveyed due to a kink in its trajectory that prevented deploying the magnetometer, so it was modeled using the North American magnetic anomaly grid. The surveyed marine magnetic Line 14 is also shorter than the modeled profile 14, so we merge both magnetic datasets using the same procedure as for the gravity data.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSeismic\u003c/b\u003e: The seismic images (Fig.\u0026nbsp;2c) are presented in Two-Way Travel Time (TWT) and were divided into three sections based on major layer boundaries: the water-seafloor and sediment-crust interfaces. To convert TWTT to depth, a constant acoustic velocity was assumed for the water layer (1480m/s \u0026ndash; as it flattens the seafloor better; Telford et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). Velocity gradients were applied for different layers: from 1550 to 2300 m/s for abyssal plain sediments; from 1550\u0026ndash;5500 m/s for sediments within the accretionary prism; and from 5500 to 7000 m/s for the crystalline crust (Deep Sea Drilling Project, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Han et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Horning et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMethodology\u003c/h3\u003e\n\u003cp\u003eWe develop integrated geophysical models along extended Lines 14 and 15 (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e and 4). For these models, the subsurface is divided into several layers that include water, sediments (several layers), crust (upper and lower), and mantle. Each layer in the model is subdivided into several blocks, which are assigned physical properties (density and magnetic susceptibility) to compute the gravity and magnetic anomalies for the model. Three parameters, namely density, magnetic susceptibility, and layer geometry, can be adjusted to ensure that the calculated gravity and magnetic anomalies align with the observed potential fields. However, some of those parameters cannot be modified as they are constrained by geophysical data and scientific drilling results. Below is the list of constraints assumed for each subsurface layer:\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eWater\u003c/strong\u003e \u003cp\u003eThe water density value of 1.03 g/cm\u003csup\u003e3\u003c/sup\u003e and zero magnetic susceptibility are assigned (Telford et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). The thickness of the water column is determined from bathymetry data (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and is fixed during modeling.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eSediments\u003c/strong\u003e \u003cp\u003eSedimentary layers are assigned densities ranging from 2.0 g/cm\u003csup\u003e3\u003c/sup\u003e (top layer) to 2.65 g/cm\u003csup\u003e3\u003c/sup\u003e (bottom layer near the subduction zone) following similar studies in this area (Ashraf, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Ashraf and Filina, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e). These high densities at the bottom of the accretionary prism are consistent with seismic refraction results of Tr\u0026eacute;hu et al. (1994) and Canales et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and are interpreted as evidence of compaction and diagenesis. A magnetic susceptibility of zero is assigned to all sediments.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eOceanic crust\u003c/strong\u003e \u003cp\u003eWe divide it into distinct upper and lower crustal units (oceanic layers II and III). This division enhances the accuracy of the models by accounting for significant variations in physical properties, especially density, between these layers (Carlson and Herrick, 1990). Density values of 2.65 g/cm\u003csup\u003e3\u003c/sup\u003e and 2.95 g/cm\u003csup\u003e3\u003c/sup\u003e for the upper and lower crust, respectively, were assigned, which are consistent with changes in P-wave crustal velocities of JdF (Tr\u0026eacute;hu et al., 1994; Gerdom et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Horning et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Canales et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The magnetic susceptibility of the Juan de Fuca plate is not very well constrained. For instance, Horning et al. (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) observed values ranging from 1,000 to 10,000 \u0026micro;cgs units in the upper crust, while Ashraf and Filina (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e) used a flat value of +/- 2000 \u0026micro;cgs with the sign relating to magnetic polarity. We assumed a single value (+/-1500 \u0026micro;cgs) for both the upper and lower crust due to limited published research differentiating magnetism between these layers. The chrons outlined in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e were used to constrain the boundaries between the normal and reversely polarized blocks of the JdF crust.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eMantle\u003c/strong\u003e \u003cp\u003eThe mantle is assigned a density of 3.3 g/cm\u003csup\u003e3\u003c/sup\u003e and zero magnetic susceptibility (Telford et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). As Moho was not imaged by RR1718 data (Fig.\u0026nbsp;2c), the depth to Moho from adjacent seismic refraction experiments was extrapolated to the study area (Canales et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Han et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). These studies suggest that the average thickness of the oceanic crust is ~\u0026thinsp;6.5 km with ~\u0026thinsp;2 km thick oceanic layer II (basalts) and ~\u0026thinsp;4.5 km thick gabbroic layer (layer III).\u003c/p\u003e \u003c/p\u003e \u003cp\u003eOnce all the parameters have been assigned, GM-SYS (Geosoft Oasis Montaj, 2021), gravity and magnetic modelling extension of Geosoft Oasis Montaj was used to compute gravity and magnetic fields for this model, and model predictions were compared with observed data. Model parameters were then adjusted to improve the fit between the predictions and the observations. It must be noted here that not all parameters can be changed as many of them are constrained with drilling, bathymetry, seismic and/or laboratory measurements (such as thickness and physical properties of water, thickness and densities of sedimentary layer, as well as published densities and magnetic susceptibilities for oceanic basalts). In addition, physical properties of each layer can vary only within a geologically appropriate range. Moreover, the same values are used for the corresponding layers of both models. Therefore, at each iteration, a careful evaluation is performed of each model parameter to ensure that adjustment does not violate a priori constraint or geologic reasoning and remain consistent for both models. When a satisfactory match is achieved with geologically plausible parameters, the model is assumed to represent the true subsurface structures.\u003c/p\u003e"},{"header":"Chapter 3 Results for different geological scenarios","content":"\u003cp\u003eSeveral integrated models were developed for two modeled profiles (aligned with Lines 14 and 15) for three different geological scenarios.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eScenario 1\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFlat Moho beneath Diebold Knoll with no crustal bending\u003c/p\u003e\n\u003cp\u003eThis scenario assumes no root beneath the Diebold Knoll seamount complex and implies that the seamount is either very young (the root has not formed yet) or was added to exceptionally strong crust that does not bend due to this load, which in both cases indicates intraplate volcanism away from the spreading center. Both modeled profiles (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) reveal important variations in physical properties within the seamount. Specifically, the uppermost part of the knoll, exposed to seawater, has a lower density of 2.6 g/cm\u003csup\u003e3\u003c/sup\u003e compared to the surrounding oceanic layer II with a density of 2.65 g/cm\u003csup\u003e3\u003c/sup\u003e. The choice of density value of 2.6 g/cm\u003csup\u003e3\u003c/sup\u003e for the top of the seamount complex (shown as a light pink color in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea and b) is justified during the sensitivity test shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec. Three different density values of 2.55, 2.60, and 2.65 g/cm\u003csup\u003e3\u003c/sup\u003e were evaluated for the topmost layer of the seamount complex in this gravity sensitivity test. Although all the values produced similar shapes of anomalies, the amplitude of computed anomaly for density value of 2.60 g/cm\u003csup\u003e3\u003c/sup\u003e resulted in the best match with the observed gravity field, suggesting a better gravity fit if the upper portion of the seamount is modeled with a lower density than the surrounding basaltic crustal layer. Additionally, this uppermost part of the knoll requires a significantly lower magnetic susceptibility of 100 \u0026micro;cgs compared to the surrounding upper crust with a magnetic susceptibility of 1500 \u0026micro;cgs to fit the observed magnetic field.\u003c/p\u003e\n\u003cp\u003eSeismic velocity analysis of seismic reflection profiles from CASIE21 supports these lower density and magnetic susceptibility values determined from our modeling. Lee et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) reported a pronounced decrease in velocity gradient within the upper part of the seamount. Lower density, reduced magnetic susceptibility, and decreased seismic P-wave velocity are also observed by other studies in the CSZ (Watts et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e; Lee et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e; Ashraf et al., \u003cspan class=\"CitationRef\"\u003e2025\u003c/span\u003e). We interpret these to be the result of faulting and hydration of the Diebold Knoll during or after its formation. These processes are documented on the JdF plate and are attributed to the subduction-related crustal bending (Nedimović et al., \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e; Ashraf et al., \u003cspan class=\"CitationRef\"\u003e2025\u003c/span\u003e). Overall, this scenario provides a reasonable fit in that portion of the model that has seismic constraints (black arrow at the bottom of Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eScenario 2\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIsostatically compensated seamount\u003c/p\u003e\n\u003cp\u003eIn this scenario, the seamount is assumed to be completely isostatically compensated. This implies that the seamount either had time to reach isostasy (i.e., relatively old), or it was added to a young and weak oceanic crust in the near-ridge settings. The root thickness is calculated using the Airy isostasy model (Airy, \u003cspan class=\"CitationRef\"\u003e1855\u003c/span\u003e; Telford et al., \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e), assuming physical properties derived in Scenario 1. This results in a 2.75 km thick root (Fig.\u0026nbsp;4a) and consequently about 10.5 mGal mismatch between calculated and observed gravity anomalies, while the magnetic anomaly is not much affected. To reconcile the gravity anomalies, this model requires an unusually high density (~\u0026thinsp;3.0 g/cm\u003csup\u003e3\u003c/sup\u003e) for the top of the seamount complex, which consequently impacts the thickness of its root. This creates a trade-off situation when either the observed gravity field is matched using anomalously high-density values for extrusive igneous rocks (which is not supported by existing literature), or a significant gravity anomaly mismatch arises due to a thick root in the model. We consider this scenario unlikely due to a significant gravity mismatch that can be removed only with geologically unrealistic density values for the seamount complex.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eScenario 3\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCrustal root thickness assigned based on analogous regional examples\u003c/p\u003e\n\u003cp\u003eIn this scenario, the root thickness beneath the Diebold Knoll is estimated based on the analysis of similar seamounts located on the Juan de Fuca plate and surveyed during two seismic cruises (Han et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e; Carbotte et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). The first one is Seamount L1-SM04, which has a height of ~\u0026thinsp;320 m above the basement and ~\u0026thinsp;230 m thick root, estimated from interpreted seismic profiles from Han et al. (\u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e). The second is seamount PD11/MCS03 from Lee et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e), which rises\u0026thinsp;~\u0026thinsp;1.14 km above the crust, and the estimated root is up to 1 km thick. Notably, all other seamounts from Lee et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) show no sign of an isostatic root beneath the crust. For both \u0026ldquo;rooted\u0026rdquo; seamounts, the computed root-to-height ratio is 0.65. Since the Diebold Knoll is situated in similar tectonic settings as these two seamounts, this ratio was used to estimate the potential thickness of the root, resulting in 0.9 km (Fig.\u0026nbsp;4b).\u003c/p\u003e\n\u003cp\u003eSince the crust bending in this case is not as pronounced as in the second scenario, the calculated gravity anomaly only exhibits up to ~\u0026thinsp;3 mGal misfit when compared to the observed gravity field. Figure\u0026nbsp;4b illustrates this mismatch, which could potentially be improved by adjusting the Moho boundary within a 0.5 km range under the seamount complex or by adding density heterogeneities within the seamount complex (less than 0.05 g/cm\u003csup\u003e3\u003c/sup\u003e with respect to values used for Fig.\u0026nbsp;4b). The exact fit for this scenario can be achieved by multiple combinations of the above-mentioned factors. However, we intentionally kept the crustal structure and physical properties consistent with\u003c/p\u003e\n\u003cp\u003eprevious scenarios and did not attempt to achieve a complete fit between observed and computed gravity fields to illustrate uncertainties of the modeling. We consider that this scenario describes a thickest reasonable root beneath Diebold Seamount based on the gravity misfit.\u003c/p\u003e"},{"header":"Chapter 4 Discussion","content":"\u003cp\u003eOur study allows us to discriminate between two potential settings of the seamount formation. The Diebold Knoll may have formed in the near-ridge settings close to the Juan de Fuca spreading center, immediately after the oceanic crust was created, implying the seamount was emplaced onto young, weak crust (our Scenario 2). Alternatively, it could have formed far from the ridge in an intraplate setting, where it would be added to older, stronger crust (Scenarios 1 and 3). The lack of direct samples from Diebold Knoll complicates the determination of its precise age, but magnetic anomaly data and cross-cutting relationships of the seamount complex and sedimentary layers can provide some age constraints.\u003c/p\u003e\n\u003cp\u003ePronounced NNE-SSW trending highs and lows in magnetic anomalies, as shown in Fig.\u0026nbsp;2b, reflect magnetic reversals, with Diebold Knoll being associated with a strong negative anomaly, indicative of a reverse polarity during its formation. The crust beneath the knoll is estimated to be around 7 to 7.5\u0026nbsp;million years old (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e and 2b), providing the oldest possible time of the knoll's emplacement after the formation of the hosting oceanic crust. There have been seven instances of magnetic reverse polarity since the formation of the crust in the vicinity of Diebold Knoll (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e), so magnetic anomaly data alone cannot resolve which of these periods corresponds to the seamount's formation. If Diebold Knoll formed near the spreading center, it would be added to a young and weak crust, and its age would likely be similar to that of the surrounding crust, with possible time ranges of formation in the late Miocene to early Pliocene (7\u0026ndash;4.7 Ma). In this case, the seamount should develop a root, as was tested in our Scenario 2 (Fig.\u0026nbsp;4a). In contrast, if it formed far from the Juan de Fuca Ridge as part of intraplate volcanism, the seamount could have been emplaced during one of the four reverse polarity periods from the mid Pliocene to late Pleistocene (4.5\u0026ndash;0.9 Ma). During this time the crust would have been relatively strong and stable to support the seamount without significant crustier flexure as described in our Scenario 1 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) and Scenario 3 (Fig.\u0026nbsp;4b). In those scenarios, we focus on the fact of the intraplate formation, and do not address the source and reasoning of the magmatic event responsible for the seamount development.\u003c/p\u003e\n\u003cp\u003eWe analyze the results from a nearby ocean drilling site and seismic reflection profiles to further constrain the age of Diebold Knoll (Fig.\u0026nbsp;6). DSDP-18 Site 174, located\u0026thinsp;~\u0026thinsp;113 km north of Diebold Knoll, provides insights into the likely composition of sediments that lap onto Diebold Knoll, although it does not directly sample the oceanic crust. Site 174 penetrated a sedimentary sequence composed of two primary units (Fig.\u0026nbsp;6b). Unit 1 (0-284 mbsf) consists of medium to very fine turbidite sand layers, interpreted as deposits from the Astoria Fan, with sediment primarily originating from the Columbia River (Kulm et al., \u003cspan class=\"CitationRef\"\u003e1973b\u003c/span\u003e; von Huene and Kulm, \u003cspan class=\"CitationRef\"\u003e1973\u003c/span\u003e; Prytulak et al., \u003cspan class=\"CitationRef\"\u003e2006\u003c/span\u003e). Unit 2 (284\u0026ndash;879 mbsf) is an abyssal plain deposit consisting of Upper Pleistocene to Pliocene basal silt, grading upward to silty clay (Fig.\u0026nbsp;6). The boundary between these two units is pronounced on seismic profiles, and the seismic reflection data from MCS01P1 (Han et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e) suggests that this boundary represents the distal edge of the current trench wedge. While age dating at Site 174 is insufficient to confirm whether this boundary represents a major depositional shift (Kulm et al., \u003cspan class=\"CitationRef\"\u003e1973a\u003c/span\u003e), the seismic data provide valuable insights into the regional sedimentary context.\u003c/p\u003e\n\u003cp\u003eRecent seismic studies (Shuck et al., \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e; Carbotte et al., \u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e) provide a framework for estimating the age of the sediments that lap onto and partially bury Diebold Knoll. A composite seismic profile (Shuck et al., in prep), extending from Vancouver Island to the Oregon/California border, crosses the MCS01P1 line and ties to well-dated ODP data from Site 1027 (Rohr et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). The deepest horizon dated by Shuck et al. (\u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e) was estimated to have an age of 0.90 Ma and is observed throughout the region (Perrin et al., in prep). We translated the depth of this horizon from the depth section of Shuck et al. (\u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e) to time sections to link to Diebold Knoll and DSDP Site 174 to give the age model (See Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e for details about tracking this link among different seismic profiles). Most of the sediment lapping onto the eastern flank of \u0026ldquo;Little Diebold\u0026rdquo; (an informal name for the buried seamount, imaged on Line 15 in Fig.\u0026nbsp;6d) corresponds to trench deposits formed since this time. This area of the Cascadia margin is characterized by thick trench deposits, interpreted to be the result of large mass transport events and related in situ deformation (Goldfinger et al., \u003cspan class=\"CitationRef\"\u003e2003\u003c/span\u003e; Tr\u0026eacute;hu et al., 2022). Correlating strata across Diebold Knoll, from seismic Line 15 to Line 14, remains challenging.\u003c/p\u003e\n\u003cp\u003eA wedge of relatively incoherent strata represents an unconformable layer that overlies well-stratified sediments filling the basement highs (Fig.\u0026nbsp;6f, Unit 1). This wedge may represent either onlapping trench sediments, the southern edge of the Astoria Fan, or a combination of both (Perrin et al., in prep). The underlying, well-stratified sediments are interpreted as older deep ocean deposits similar to Unit 2 sampled at Site 174. These findings, combined with the regional basement topography, suggest that Diebold Knoll might have been extruded onto a rough basement, as evidenced by significant variations in the thickness of the strata that filled the basement low in the central part of Line 14 (Fig.\u0026nbsp;6f).\u003c/p\u003e\n\u003cp\u003eFurther east of \"Little Diebold\", onlapping sediments are predominantly trench deposits, including thick, internally incoherent layers interpreted as mass transport events younger than ~\u0026thinsp;0.90 Ma (Tr\u0026eacute;hu et al., 2022). Some of these deposits appear to have overtopped a now-buried seamount, with disruption of the boundary between the two deposits indicating that the younger mass transport event may have scoured the seafloor, removing a thin layer of inter-event sedimentation. These deposits are absent in the shallow basin separating \"Little Diebold\" from Diebold Knoll (Tr\u0026eacute;hu et al., 2022).\u003c/p\u003e\n\u003cp\u003eTogether, the seismic data and the stratigraphic relationships suggest that Diebold Knoll formed in a geologically complex region, potentially involving multiple depositional and volcanic processes. While the precise timing of its emplacement remains uncertain, our integrated analysis, particularly the stratigraphic relationships with sediments older than 0.9 Ma and a lack of isostatic equilibrium suggested by our modeling, strongly supports an intraplate origin for Diebold Knoll. This implies that the seamount likely formed during a period of reverse magnetic polarity in the mid-Pliocene (4.5 Ma) to late Pleistocene (older than 0.9 Ma), consistent with emplacement on strong, mature lithosphere. Future studies, particularly those incorporating direct geological samples, will be critical to refining these age estimates and resolving the complex interactions between Diebold Knoll, the surrounding crust, and regional tectonic processes.\u003c/p\u003e"},{"header":"Chapter 5 Conclusions","content":"\u003cp\u003eThis study integrates multiple geophysical datasets to construct a detailed model of the crustal architecture and physical properties of Diebold Knoll, which resides on ~\u0026thinsp;7 Myr old oceanic Juan de Fuca lithosphere\u0026thinsp;~\u0026thinsp;60 km to the west of the subduction front. We conclude that the uppermost portion of Diebold Knoll (~\u0026thinsp;1 km above the basement) exhibits a lower density (2.6 g/cm\u0026sup3;) and a significantly reduced magnetic susceptibility (100 \u0026micro;cgs) compared to the surrounding upper oceanic crust of the Juan de Fuca plate (2.655 g/cm\u0026sup3; and 1500 \u0026micro;cgs). These lower physical properties suggest faulting and hydration processes occurring during or after the formation of the seamount, consistent with recent seismic surveys reporting a reduced seismic velocity gradient in this region. The rest of the seamount complex has physical properties similar to surrounding oceanic crust, indicating it is primarily composed of materials with similar densities and magnetic susceptibilities.\u003c/p\u003e \u003cp\u003eOur modeling suggests that Diebold Knoll is either located over a flat Moho or possesses a very thin (\u0026le;\u0026thinsp;1 km) crustal root, suggesting it was emplaced in the intraplate settings and is not isostatically compensated. The seamount was added to the lithosphere, old enough to support the weight of the seamount without significant crustal deformation. The entire seamount complex is reversely magnetized, pointing to several potential time intervals for its formation: two in the Miocene, three in the Pliocene, and two in the Quaternary. Recent work by Shuck et al. (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) and Carbotte et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) offers valuable stratigraphic correlations of ocean drilling data with regional seismic profiles in CSZ that may help refine these age estimates. Incorporating the results of their analysis suggests that the seamount's emplacement could have occurred as recently as the late Pliocene to late Pleistocene (4.5\u0026ndash;0.9 Ma).\u003c/p\u003e \u003cp\u003eThe physical property variations within Diebold Knoll and its complex stratigraphic relationships offer key constraints for understanding the geologic evolution of the Cascadia subduction zone (CSZ). These findings contribute to our understanding of seamount formation, its interactions with the surrounding crust, and its potential role in subduction zone dynamics. Moreover, the integrated approach used here, combining seismic data, magnetic properties, and stratigraphic correlations, provides a framework for studying crustal structure, physical property heterogeneities, and the age of formation in other regions hosting intraplate seamounts.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eCompeting interests:\u003c/strong\u003e \u003cp\u003eThe authors acknowledge that there are no conflicts of interest recorded.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eEthical approval:\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.A.I. and I.F. contributed to the conceptualization of the study. M.A.I. performed most of the data analysis and led the investigation and manuscript writing. I.F. and A.M.T. provided supervision and contributed to manuscript editing and revisions. A.M.T. contributed to figure preparation. All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments:\u003c/h2\u003e \u003cp\u003eThis research was supported by the Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln.\u003c/p\u003e\u003ch2\u003eData availability:\u003c/h2\u003e \u003cp\u003eAll the data that support the findings of this study are open access. Please see the relevant citations for the data URL.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAiry GB (1855) On the computation of the effect of the attraction of mountain-masses, as disturbing the apparent astronomical latitude of stations in geodetic surveys: Philosophical Transactions of the Royal Society of London, v. 145. 101\u0026ndash;104. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1098/RSTL.1855.0003\u003c/span\u003e\u003cspan address=\"10.1098/RSTL.1855.0003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAshraf A (2021) Geological Structures and Crustal Architecture of the Cascadia Subduction Zone from the Integration of Multiple Geophysical Datasets: University of Nebraska-Lincoln, doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://digitalcommons.unl.edu/geoscidiss/135\u003c/span\u003e\u003cspan address=\"https://digitalcommons.unl.edu/geoscidiss/135\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAshraf A, Filina I (2023a) New 2.75-D gravity modeling reveals the low-density nature of propagator wakes in the Juan de Fuca plate: Tectonophysics, v. 869. 230127. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.tecto.2023.230127\u003c/span\u003e\u003cspan address=\"10.1016/j.tecto.2023.230127\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAshraf A, Filina I (2023b) Zones of Weakness Within the Juan de Fuca Plate Mapped From the Integration of Multiple Geophysical Data and Their Relation to Observed Seismicity: Geochemistry, Geophysics, Geosystems, v. 24. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2023GC010943\u003c/span\u003e\u003cspan address=\"10.1029/2023GC010943\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAshraf A, Hooft EEE, Toomey DR, Tr\u0026eacute;hu AM, Nolan S, Wirth EA, Ward KM (2025) A High-Resolution 3-DP-Wave Velocity Structure of the South-Central Cascadia Subduction Zone From Wide-Angle Shore-Crossing Seismic Refraction Data: Journal of Geophysical Research: Solid Earth, v. 130, p. e2024JB029525\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAtwater BF, Hemphill-Haley E (1997) Recurrence intervals for great earthquakes of the past 3,500 years at northeastern Willapa Bay. Professional Paper, Washington. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3133/PP1576\u003c/span\u003e\u003cspan address=\"10.3133/PP1576\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAtwater BF, Musumi-Rokkaku S, Satake K, Tsuji Y, Ueda K, Yamaguchi DK (2015) The orphan tsunami of 1700\u0026mdash;Japanese clues to a parent earthquake in North America:, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3133/pp1707\u003c/span\u003e\u003cspan address=\"10.3133/pp1707\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBankey V et al (2002) Digital data grids for the magnetic anomaly map of North America: Open-File Report. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3133/OFR02414\u003c/span\u003e\u003cspan address=\"10.3133/OFR02414\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBilek SL, Schwartz SY, DeShon HR (2003) Control of seafloor roughness on earthquake rupture behavior: Geology, v. 31. 455\u0026ndash;458. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1130/0091-7613(2003)031%3C0455:COSROE%3E2.0.CO;2\u003c/span\u003e\u003cspan address=\"10.1130/0091-7613(2003)031%3C0455:COSROE%3E2.0.CO;2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBodmer M, Toomey DR, Hooft EEE, Schmandt B (2018) Buoyant Asthenosphere Beneath Cascadia Influences Megathrust Segmentation: Geophysical Research Letters, v. 45. 6954\u0026ndash;6962. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2018GL078700\u003c/span\u003e\u003cspan address=\"10.1029/2018GL078700\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBurgette RJ, Weldon RJ, Schmidt DA (2009) Interseismic uplift rates for western Oregon and along-strike variation in locking on the Cascadia subduction zone. J Geophys Research: Solid Earth v 114. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2008JB005679\u003c/span\u003e\u003cspan address=\"10.1029/2008JB005679\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCanales JP, Carbotte SM, Nedimovic MR, Carton H (2017) Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone: Nature Geoscience, v. 10. 864\u0026ndash;870. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/NGEO3050\u003c/span\u003e\u003cspan address=\"10.1038/NGEO3050\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarbotte SM et al (2024) Subducting plate structure and megathrust morphology from deep seismic imaging linked to earthquake rupture segmentation at Cascadia. Sci Adv v 10. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1126/sciadv.adl3198\u003c/span\u003e\u003cspan address=\"10.1126/sciadv.adl3198\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarbotte S, Boston B, Han S (2022) Multi-Channel Seismic Shot Data from the Cascadia margin acquired during Langseth cruise MGL2104 (2021): IDEA\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eProject DSD (1989) Archive of Core and Site/Hole Data and Photographs from the Deep Sea Drilling Project (DSDP): National Geophysical Data Center, NOAA, doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.7289/V54M92G2\u003c/span\u003e\u003cspan address=\"10.7289/V54M92G2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFleming SW, Trehu AM (1999) Crustal structure beneath the central Oregon convergent margin from potential-field modeling: Evidence for a buried basement ridge in local contact with a seaward dipping\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGerdom M, Trehu AM, Flueh ER, Klaeschen D (2000) The continental margin off Oregon from seismic investigations: Tectonophysics, v. 329. 79\u0026ndash;97. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/S0040-1951(00)00190-6\u003c/span\u003e\u003cspan address=\"10.1016/S0040-1951(00)00190-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoldfinger C et al (2012) Turbidite event history\u0026mdash;Methods and implications for Holocene paleoseismicity of the Cascadia subduction zone: Professional Paper. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3133/PP1661F\u003c/span\u003e\u003cspan address=\"10.3133/PP1661F\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoldfinger C, Galer S, Beeson J, Hamilton T, Black B, Romsos C, Patton J, Nelson CH, Hausmann R, Morey A (2017) The importance of site selection, sediment supply, and hydrodynamics: A case study of submarine paleoseismology on the northern Cascadia margin, Washington USA: Marine Geology, v. 384. 4\u0026ndash;46. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.margeo.2016.06.008\u003c/span\u003e\u003cspan address=\"10.1016/j.margeo.2016.06.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoldfinger C, Nelson CH, Johnson JE (2003) Holocene Earthquake Records from the Cascadia Subduction Zone and Northern San Andreas Fault Based on Precise Dating of Offshore Turbidites: Annual Review of Earth and Planetary Sciences, v. 31. 555\u0026ndash;577. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1146/annurev.earth.31.100901.141246\u003c/span\u003e\u003cspan address=\"10.1146/annurev.earth.31.100901.141246\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHan S, Carbotte SM, Canales JP, Nedimović MR, Carton H (2018) Along-Trench Structural Variations of the Subducting Juan de Fuca Plate From Multichannel Seismic Reflection Imaging. J Geophys Research: Solid Earth v 123:3122\u0026ndash;3146. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/2017JB015059\u003c/span\u003e\u003cspan address=\"10.1002/2017JB015059\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHan S, Carbotte SM, Canales JP, Nedimovic MR, Carton H, Gibson JC, Horning GW (2016) Seismic reflection imaging of the Juan de Fuca plate from ridge to trench: New constraints on the distribution of faulting and evolution of the crust prior to subduction. J Geophys Research: Solid Earth v 121:1849\u0026ndash;1872. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/2015JB012416\u003c/span\u003e\u003cspan address=\"10.1002/2015JB012416\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHolbrook WS, Kent G, Keranen K, Johnson HP, Trehu A, Tobin H, Caplan-Auerbach J, Beeson J (2012) Cascadia fore arc seismic survey: Open-access data available: Eos, Transactions American Geophysical Union, v. 93. 521\u0026ndash;522. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2012EO500002\u003c/span\u003e\u003cspan address=\"10.1029/2012EO500002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHorning G, Canales JP, Carbotte SM, Han S, Carton H, Nedimović MR, van Keken PE (2016) A 2-D tomographic model of the Juan de Fuca plate from accretion at axial seamount to subduction at the Cascadia margin from an active source ocean bottom seismometer survey. J Geophys Research: Solid Earth v 121:5859\u0026ndash;5879. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/2016JB013228\u003c/span\u003e\u003cspan address=\"10.1002/2016JB013228\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evon Huene R, Kulm LD (1973) Tectonic Summary of Leg 18, \u003cem\u003ein\u003c/em\u003e Initial Reports of the Deep Sea Drilling Project, 18, U.S. Government Printing Office. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2973/dsdp.proc.18.133.1973\u003c/span\u003e\u003cspan address=\"10.2973/dsdp.proc.18.133.1973\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIslam MA, Crustal structures of Diebold Knoll and adjacent Juan De Fuca oceanic crust from integration of seismic, gravity and magnetic data: University of Nebraska-, Lincoln (2023) \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://digitalcommons.unl.edu/geoscidiss/151/\u003c/span\u003e\u003cspan address=\"https://digitalcommons.unl.edu/geoscidiss/151/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (accessed August 2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKodaira S, Takahashi N, Nakanishi A, Miura S, Kaneda Y (2000) Subducted Seamount Imaged in the Rupture Zone of the 1946 Nankaido Earthquake: Science, v. 289. 104\u0026ndash;106. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1126/SCIENCE.289.5476.104\u003c/span\u003e\u003cspan address=\"10.1126/SCIENCE.289.5476.104\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKulm LD et al (1973a) Site 174, \u003cem\u003ein\u003c/em\u003e Initial Reports of the Deep Sea Drilling Project, 18, U.S. Government Printing Office. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2973/dsdp.proc.18.105.1973\u003c/span\u003e\u003cspan address=\"10.2973/dsdp.proc.18.105.1973\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKulm LD, Prince RA, Snavely PD (1973b) Site Survey of the Northern Oregon Continental Margin and Astoria Fan, \u003cem\u003ein\u003c/em\u003e Initial Reports of the Deep Sea Drilling Project, 18, U.S. Government Printing Office. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2973/dsdp.proc.18.app1a.1973\u003c/span\u003e\u003cspan address=\"10.2973/dsdp.proc.18.app1a.1973\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee M, Carbotte SM, Shuck B, Han S, Boston B, Lee M, Carbotte SM, Shuck B, Han S, Boston B (2022) Examining sediment consolidation state and hydrothermal circulation at and near buried seamounts on the Cascadia Margin and its relation to earthquake generation: AGUFM, v. 2022, p. T42D-0147. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://ui.adsabs.harvard.edu/abs/2022AGUFM.T42D0147L/abstract\u003c/span\u003e\u003cspan address=\"https://ui.adsabs.harvard.edu/abs/2022AGUFM.T42D0147L/abstract\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (accessed May 2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcCaffrey R, King RW, Payne SJ, Lancaster M (2013) Active tectonics of northwestern U.S. inferred from GPS-derived surface velocities. J Geophys Research: Solid Earth v 118:709\u0026ndash;723. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2012JB009473\u003c/span\u003e\u003cspan address=\"10.1029/2012JB009473\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcCaffrey R, Qamar AI, King RW, Wells R, Khazaradze G, Williams CA, Stevens CW, Vollick JJ, Zwick PC (2007) Fault locking, block rotation and crustal deformation in the Pacific Northwest. Geophys J Int v 169:1315\u0026ndash;1340. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/j.1365-246X.2007.03371.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1365-246X.2007.03371.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMelgar D (2021) Was the January 26th, 1700 Cascadia Earthquake Part of a Rupture Sequence? Journal of Geophysical Research: Solid Earth, v. 126, p. e2021JB021822. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2021JB021822\u003c/span\u003e\u003cspan address=\"10.1029/2021JB021822\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNedimović MR, Bohnenstiehl DWR, Carbotte SM, Pablo Canales J, Dziak RP (2009) Faulting and hydration of the Juan de Fuca plate system: Earth and Planetary Science Letters, v. 284. 94\u0026ndash;102. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.epsl.2009.04.013\u003c/span\u003e\u003cspan address=\"10.1016/j.epsl.2009.04.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorvell B, Kyritz T, Spinelli GA, Harris RN, Dickerson K, Tr\u0026eacute;hu AM, Carbotte S, Han S, Boston B, Lee M (2023) Thermally Significant Fluid Seepage Through Thick Sediment on the Juan de Fuca Plate Entering the Cascadia Subduction Zone: Geochemistry, Geophysics, Geosystems, v. 24, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2023GC010868\u003c/span\u003e\u003cspan address=\"10.1029/2023GC010868\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eParsons T et al (2005) Crustal Structure of the Cascadia Fore Arc of Washington:, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://pubs.usgs.gov/pp/pp1661-D\u003c/span\u003e\u003cspan address=\"http://pubs.usgs.gov/pp/pp1661-D\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrytulak J, Vervoort JD, Plank T, Yu C (2006) Astoria Fan sediments, DSDP site 174, Cascadia Basin: Hf\u0026ndash;Nd\u0026ndash;Pb constraints on provenance and outburst flooding: Chemical Geology, v. 233. 276\u0026ndash;292. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/J.CHEMGEO.2006.03.009\u003c/span\u003e\u003cspan address=\"10.1016/J.CHEMGEO.2006.03.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRogers GC (1988) An assessment of the megathrust earthquake potential of the Cascadia subduction zone 1:, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1139/e88-083\u003c/span\u003e\u003cspan address=\"10.1139/e88-083\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRohr KMM, King H, Riedel M, Schmidt U (2019) From mid-plate to subduction zone: stratigraphy of the northeast Juan de Fuca Plate. offshore Br Columbia. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4095/314906\u003c/span\u003e\u003cspan address=\"10.4095/314906\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRyan WBF et al (2009) Global multi-resolution topography synthesis: Geochemistry, Geophysics. Geosyst v 10. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2008GC002332\u003c/span\u003e\u003cspan address=\"10.1029/2008GC002332\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSandwell DT, M\u0026uuml;ller RD, Smith WHF, Garcia E, Francis R (2014) New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure: Science, v. 346. 65\u0026ndash;67. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1126/SCIENCE.1258213\u003c/span\u003e\u003cspan address=\"10.1126/SCIENCE.1258213\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSatake K, Wang K, Geophysical BA-J, of (2003) and undefined, 2003, Fault slip and seismic moment of the 1700 Cascadia earthquake inferred from Japanese tsunami descriptions: Wiley Online Library, v. 108, p. 2535. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2003JB002521\u003c/span\u003e\u003cspan address=\"10.1029/2003JB002521\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchmalzle GM, McCaffrey R, Creager KC (2014) Central Cascadia subduction zone creep: Geochemistry, Geophysics, Geosystems, v. 15. 1515\u0026ndash;1532. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/2013GC005172\u003c/span\u003e\u003cspan address=\"10.1002/2013GC005172\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShuck B, Babendreier C, Han S, Carbotte SM, Beeson JW, Boston B, Tobin HJ, Lee M (2023) A New Regional Stratigraphic Framework for the Cascadia Oceanic Basin, \u003cem\u003ein\u003c/em\u003e AGU Fall Meeting Abstracts, v. 2023, p. T53E\u0026ndash;0197\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh SC et al (2011) Aseismic zone and earthquake segmentation associated with a deep subducted seamount inSumatra: Nature Geoscience, v. 4. 308\u0026ndash;311. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/ngeo1119\u003c/span\u003e\u003cspan address=\"10.1038/ngeo1119\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSpinelli GA, Harris RN (2011) Thermal effects of hydrothermal circulation and seamount subduction: Temperatures in the Nankai Trough Seismogenic Zone Experiment transect, Japan: Geochemistry, Geophysics, Geosystems, v. 12, p. n/a-n/a. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2011GC003727\u003c/span\u003e\u003cspan address=\"10.1029/2011GC003727\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTelford WM, Geldart LP, Sheriff RE (1990) Appl Geophysics: Appl Geophys. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1017/CBO9781139167932\u003c/span\u003e\u003cspan address=\"10.1017/CBO9781139167932\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTominaga M (2017a) Gravimeter (Bell BGM-3) data as collected during the cruise RR1718, Collaborative EAGER project: Early Career Seismic Chief Scientist Training Cruise. Rolling Deck to Repository (R2R). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.7284/128301\u003c/span\u003e\u003cspan address=\"10.7284/128301\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTominaga M (2017b) Magnetometer (MarineMagnetics SeaSPY) data as collected during the cruise RR1718, Collaborative EAGER project: Early Career Seismic Chief Scientist Training Cruise. Rolling Deck to Repository (R2R). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.7284/128302\u003c/span\u003e\u003cspan address=\"10.7284/128302\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTominaga M, Trehu A, Lyle M (2018) Multi-Channel Seismic Shot Data from the Seismic Early Career Chief Scientist Training Cruise 2017, Cascadia Margin, acquired during R/V Roger Revelle expedition RR1718 (2017). IEDA:, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1594/IEDA/324504\u003c/span\u003e\u003cspan address=\"10.1594/IEDA/324504\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrehu AM, Asudeh I, Brocher TM, Luetgert JH, Mooney WD, Nabelek JL, Nakamura Y (1994) Crustal Architecture of the Cascadia Forearc: Science, v. 266, pp. 237\u0026ndash;243, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1126/SCIENCE.266.5183.237\u003c/span\u003e\u003cspan address=\"10.1126/SCIENCE.266.5183.237\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrehu AM, Blakely RJ, Williams MC (2012) Subducted seamounts and recent earthquakes beneath the central cascadia forearc: Geology, v. 40. 103\u0026ndash;106. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1130/G32460.1\u003c/span\u003e\u003cspan address=\"10.1130/G32460.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrehu AM, Braunmiller J, Davis E (2015) Seismicity of the Central Cascadia Continental Margin near 44.5 N: A Decadal View: Seismological Research Letters, v. 86. 819\u0026ndash;829. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1785/0220140207\u003c/span\u003e\u003cspan address=\"10.1785/0220140207\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrehu AM, Tominaga M, Lyle M, Davenport K, Phrampus BJ, Favorito J, Zhang E, Lenz BL, Shreedharan S, Yelisetti S (2022) The Hidden History of the South-Central Cascadia Subduction Zone Recorded on the Juan de Fuca Plate Offshore Southwest Oregon: Geochemistry, Geophysics, Geosystems, v. 23, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2021GC010318\u003c/span\u003e\u003cspan address=\"10.1029/2021GC010318\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWalker JD, Geissman JW (2022) Geologic Time Scale v. 6.0 - The Geological Society of America:, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1130/2022.CTS006C\u003c/span\u003e\u003cspan address=\"10.1130/2022.CTS006C\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWalton MAL et al (2021) Toward an Integrative Geological and Geophysical View of Cascadia Subduction Zone Earthquakes: Annual Review of Earth and Planetary Sciences, v. 49. 367\u0026ndash;398. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1146/annurev-earth-071620-065605\u003c/span\u003e\u003cspan address=\"10.1146/annurev-earth-071620-065605\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang K, Bilek SL (2011) Do subducting seamounts generate or stop large earthquakes? Geology, v. 39. 819\u0026ndash;822. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1130/G31856.1\u003c/span\u003e\u003cspan address=\"10.1130/G31856.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang K, Bilek SL (2014) Invited review paper: Fault creep caused by subduction of rough seafloor relief: Tectonophysics, v. 610. 1\u0026ndash;24. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/J.TECTO.2013.11.024\u003c/span\u003e\u003cspan address=\"10.1016/J.TECTO.2013.11.024\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatts AB, Grevemeyer I, Shillington DJ, Dunn RA, Boston B, de la G\u0026oacute;mez L (2021) Seismic Structure, Gravity Anomalies and Flexure Along the Emperor Seamount Chain: Journal of Geophysical Research: Solid Earth, v. 126, p. e2020JB021109. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2020JB021109\u003c/span\u003e\u003cspan address=\"10.1029/2020JB021109\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatts AB, Koppers AAP, Robinson DP (2010) Seamount Subduction and Earthquakes: Source: Oceanography, v. 23. 166\u0026ndash;173. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2307/24861080\u003c/span\u003e\u003cspan address=\"10.2307/24861080\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilson DS (1988) Tectonic history of the Juan de Fuca Ridge over the last 40 million years. J Geophys Res v 93. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/jb093ib10p11863\u003c/span\u003e\u003cspan address=\"10.1029/jb093ib10p11863\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilson DS (2002) The Juan de Fuca plate and slab: isochron structure and Cenozoic plate motions:, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4095/222387\u003c/span\u003e\u003cspan address=\"10.4095/222387\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"Seamounts, seafloor topography, Cascadia Subduction Zone, Gravity model, Magnetic model","lastPublishedDoi":"10.21203/rs.3.rs-8689065/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8689065/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSubducting seamounts are thought to be a major factor affecting subduction zone processes, although details of their impact remain poorly understood. Incorporating seamounts into geodynamic models requires accurate knowledge of their density structure and tectonic history, but determining these parameters is challenging, especially when the seamounts are partially or completely buried by a thick sediment cover on the subducting plate. We focus on an intraplate seamount known as Diebold Knoll, which is evident in bathymetry approximately 60 km west of the Cascadia subduction zone deformation front. The objectives of this research are to determine the settings the Diebold Knoll was formed and to evaluate heterogeneities in the physical properties of oceanic crust resulting from its addition. We present an integrated geophysical analysis combining seismic reflection data, gravity, and magnetic anomalies along two intersecting profiles across the seamount. Our gravity analysis reveals that Diebold Knoll is not isostatically compensated and may have up to 1 km thick root. Our modeling suggests that the top\u0026thinsp;~\u0026thinsp;1 km of the seamount exhibits lower values of density (2.6 g/cm\u0026sup3;) and magnetic susceptibility (100 \u0026micro;cgs) relative to the adjacent crust, attributed to syn-formation faulting and post-formation hydration. The negative magnetic anomaly of the seamount and the stratigraphic relationships of the seamount complex and the hosting sedimentary layers, including the presence of a 0.9 Ma horizon, indicate that Diebold Knoll is considerably younger (4.5\u0026ndash;0.9 Ma) than the underlying oceanic crust (7-7.5 Ma) and was formed in the intraplate settings.\u003c/p\u003e","manuscriptTitle":"Tectonic History of Diebold Knoll from Integration of Seismic, Gravity and Magnetic Data","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-03 10:39:18","doi":"10.21203/rs.3.rs-8689065/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":"7e060905-0241-4e32-a56d-2afce355ee7c","owner":[],"postedDate":"February 3rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-07T10:25:16+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-03 10:39:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8689065","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8689065","identity":"rs-8689065","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}