Simplified frontal thrust splay fault geometries at the Cascadia Subduction Zone mapped using multi-channel seismic (MCS) reflection data

This dataset contains offshore fault geometries for frontal thrust splay faults in the Cascadia Subduction Zone (CSZ) that were mapped and developed for use in 3D ground motion simulations (Dunham and others, 2025). There are a total of 6 thrust faults (A-F), three of the faults (A-C) were mapped by interpretation of seismic reflection data (Ledeczi and others, 2024; Lucas and others, 2025) from the ultra-long offset seismic reflection imagery collected during the CASIE21 experiment (Carbotte and others, 2023). Fault D is also mapped using the CASIE21 seismic data but only using a single seismic line, so has fewer constraints and is processed using the methods outlined for Faults E and F. Faults E and F were interpreted primarily using legacy seismic data from the Mendocino Triple Junction Seismic Experiment (1994) and interpretations in Gulick and others (1998). We present this data in two formats, files that contain 2D seismic picks from the interpretation of the seismic data and interpolated fault geometries that are included in the final kinematic earthquake rupture models. We also include the mapview location of the deformation front, which is approximated as a continuous boundary and defined by where the incoming sediment section atop the downgoing Juan de Fuca Plate is observed to be deformed in CASIE21 seismic reflection imagery (Lucas and others, 2025). The deformation front is interpolated between 2D seismic lines using high-resolution USGS 30-meter bathymetry compilations (Dartnell and others, 2023, 2026; Beeson and others, 2025) and 50-meter GMRT (Global Multi-Resolution Topography) bathymetry compilation (Ryan and others, 2009). Note that the deformation front is not the megathrust fault location, but instead where accretionary wedge deformation begins. See references.pdf for full in-text citation information.
 
Beeson, J. W., P. Dartnell, and J. T. Watt, 2025, Composite bathymetric surface of the northern Cascadia Margin offshore Washington, U.S. Geological Survey data release.
Carbotte, S. M., B. Boston, S. Han, B. Shuck, J. Beeson, J. P. Canales, H. Tobin, N. Miller, M. Nedimovic, A. Tréhu, and others, 2024, Subducting plate structure and megathrust morphology from deep seismic imaging linked to earthquake rupture segmentation at Cascadia, Sci. Adv, 10, doi: 10.1126/sciadv.adl3198.
Carbotte, S., S. Han, B. Boston, and J. Canales, 2023, Processed pre-stack depth-migrated seismic reflection data from the 2021 CASIE21 multi-channel seismic survey (MGL2104).
Dartnell, P., J. A. Rudebusch, J. E. Conrad, J. T. Watt, and J. C. Hill, 2026, Composite multibeam bathymetry surface and data sources of the southern Cascadia Margin offshore Oregon and northern California (version 2.0, April 2026), U.S. Geological Survey data release.
Dartnell, P., J. T. Watt, J. C. Hill, and J. E. Conrad, 2023, Composite multibeam bathymetry surface and data sources of the central Cascadia Margin offshore Oregon, U.S. Geological Survey data release.
Dunham, A. M., E. M. Wirth, A. Grant, and A. Frankel, 2025, “CSZ full-margin megathrust earthquake scenarios”, in 3D broadband ground shaking simulations of Cascadia Subduction Zone earthquake scenarios [Version 2], DesignSafe-CI, doi: 10.17603/ds2-dqrm-dh11.
Gulick, S. P. S., A. M. Meltzer, and S. H. Clarke, 1998, Seismic structure of the southern Cascadia subduction zone and accretionary prism north of the Mendocino triple junction, J. Geophys. Res. Solid Earth, 103, no. B11, 27207–27222, doi: 10.1029/98jb02526.
Ledeczi, A., M. Lucas, H. Tobin, J. Watt, and N. Miller, 2024, Late Quaternary Surface Displacements on Accretionary Wedge Splay Faults in the Cascadia Subduction Zone: Implications for Megathrust Rupture, Seismica, 2, no. 4, doi: 10.26443/seismica.v2i4.1158.
Lucas, M. C., A. M. Ledeczi, H. J. Tobin, S. M. Carbotte, J. T. Watt, S. Han, B. Boston, and D. Jiang, 2025, No evidence for an active margin-spanning megasplay fault at the Cascadia Subduction Zone, Seismica, 2, doi: 10.26443/seismica.v2i4.1477.
McCrory, P. A., J. L. Blair, F. Waldhauser, and D. H. Oppenheimer, 2012, Juan de Fuca slab geometry and its relation to Wadati-Benioff zone seismicity, J. Geophys. Res., 117, no. B09306, 1–23, doi: 10.1029/2012JB009407.
Ryan, W. B. F., S. M. Carbotte, J. O. Coplan, S. O’Hara, A. Melkonian, R. Arko, R. A. Weissel, V. Ferrini, A. Goodwillie, F. Nitsche, and others, 2009, Global multi-resolution topography synthesis, Geochemistry, Geophysics, Geosystems, 10, no. 3, doi: 10.1029/2008GC002332.
Stephenson, W. J., N. G. Reitman, and S. J. Angster, 2017, P- and S-wave velocity models incorporating the Cascadia subduction zone for 3D earthquake ground motion simulations—Update for Open-File Report 2007–1348, US Geological Society Open File Report 2017-1152, 1–17, doi: 10.3133/ofr20171152.