John H. Shaw

v2: added MRST well-rate outputs (wellSols_qOs_m3s.mat, wellSols_qWs_m3s.mat) for Fig. 10; expanded README figure-provenance.Data underlying a multiphase-flow and geomechanics modeling study of the Wilmington Oil Field (Los Angeles Basin, California), assessing production- and injection-induced subsidence, stress evolution, and fault stability over the field's operational history (1936–2020). The deposit contains the finite-element and reservoir-simulation grids, raw and processed well production/injection records (derived from CalGEM public data), processed pressure and stress fields exchanged between the flow (MRST) and geomechanical (Abaqus) models, and the curated simulation outputs used to generate the paper's figures. Companion code: 10.5281/zenodo.20723535. The SCEC Community Stress Model used to initialize one stress scenario is third-party and cited at source, not redistributed here. Associated manuscript: Saló-Salgado et al. (2026), in review (preprint: arXiv:2605.16711). Licensed CC-BY-4.0.

Abstract Using seismic reflection profiles, historical well logging data, and luminescence and radiocarbon ages, we determine a Pleistocene‐Holocene slip history for the central, Santa Fe Springs segment of the Puente Hills blind‐thrust fault (PHT), a major seismogenic fault situated beneath the urbanized Los Angeles metropolitan region. We analyze the geometry of correlative stratigraphic units in the forelimb and backlimb of the overlying growth‐fold, the Santa Fe Springs anticline, and determine the uplift of seven age‐correlative markers. Uplift measurements are converted to thrust displacements on the underlying PHT using a structural method laid out by Don et al. (2022, https://doi.org/10.1785/0120220048 ) that accounts for the geometry of the fault. These data indicate that deep thrust displacement on the PHT is partially consumed updip in the creation of a hanging‐wall fault‐bend fold, with forelimb growth strata recording <80% of the slip documented within the backlimb. Chronological data from growth strata yield age constraints for folding and faulting on the underlying PHT, providing a detailed incremental slip history derived from both the forelimb and backlimb folding for seven discrete growth horizons, spanning the past 1.4 million years. The resulting six incremental slip rates demonstrate that fault slip has varied through time from the middle Pleistocene to the Holocene. Moreover, these results reveal synchronous acceleration of both the central, Santa Fe Springs and western, Los Angeles segments of the fault system since late Pleistocene time (after 200 ka) and slip rates of greater than 2 mm/yr on the downdip, backlimb, fault‐ramp below the anticline.

Nearly a century of oil production in the Wilmington Oil Field, Los Angeles Basin, California, has modified the stress state, caused nearly 9 m of ground surface subsidence, and been associated with earthquakes that sheared wells. This offers a unique opportunity to elucidate the processes that govern these phenomena: Since the 1930s, approximately 2.5 billion barrels of oil have been produced, accompanied by water injection volumes roughly an order of magnitude larger. Combined with extensive structural and geophysical constraints, this history allows us to interrogate the long-term geomechanical impacts of reservoir operations. Here, we assess (i) how the initial stress state, typically uncertain in the shallow crust ($<5$ km depth), influences subsidence and uplift, and (ii) how production and injection operations affect fault stability. Our numerical model, calibrated with published measurements of reservoir pressures and surface displacements, incorporates a detailed representation of fault surfaces within and around the field, well-level production and injection schedules, and an elastoplastic constitutive framework. Model results show that the previously assumed stress regime in the field (reverse faulting) needs to be reassessed$\unicode{x2014}$the best match to the ground deformation data is achieved when the sedimentary section is initialized with low deviatoric stress (i.e., not critically stressed). This suggests significant variation in the stress state with depth, including a likely change in the stress regime. DCFF values suggest minor destabilization on reservoir faults and larger changes on sub-horizontal bedding planes; both could explain the faulting that led to sheared wells and seismicity between 1947 and 1961.

Nearly a century of oil production in the Wilmington Oil Field, Los Angeles Basin, California, has modified the stress state, caused nearly 9 m of ground surface subsidence, and been associated with earthquakes that sheared wells. This offers a unique opportunity to elucidate the processes that govern these phenomena: Since the 1930s, approximately 2.5 billion barrels of oil have been produced, accompanied by water injection volumes roughly an order of magnitude larger. Combined with extensive structural and geophysical constraints, this history allows us to interrogate the long-term geomechanical impacts of reservoir operations. Here, we assess (i) how the initial stress state, typically uncertain in the shallow crust ($<5$ km depth), influences subsidence and uplift, and (ii) how production and injection operations affect fault stability. Our numerical model, calibrated with published measurements of reservoir pressures and surface displacements, incorporates a detailed representation of fault surfaces within and around the field, well-level production and injection schedules, and an elastoplastic constitutive framework. Model results show that the previously assumed stress regime in the field (reverse faulting) needs to be reassessed$\unicode{x2014}$the best match to the ground deformation data is achieved when the sedimentary section is initialized with low deviatoric stress (i.e., not critically stressed). This suggests significant variation in the stress state with depth, including a likely change in the stress regime. DCFF values suggest minor destabilization on reservoir faults and larger changes on sub-horizontal bedding planes; both could explain the faulting that led to sheared wells and seismicity between 1947 and 1961.

ABSTRACT We present a new version of the Statewide California Earthquake Center (SCEC) Community Fault Model (CFM 6.1) for southern California that describes more than 400 active faults that accommodate relative motions across the Pacific-North American plate boundary. CFM 6.1 is a substantially enhanced representation of the southern California fault system, with systematically updated and improved fault surfaces using detailed fault traces, precisely relocated earthquake and machine learning-enabled hypocenter catalogs (Ross, Trugman, et al., 2019), and new focal mechanism solutions (Lin et al., 2007; Hauksson et al., 2012 + updates; Yang et al., 2012), among other datasets. Several of the new fault representations, such as for the 2019 Ridgecrest, California (M 6.4 and 7.1) events, were developed using an objective, constraint-based interpolation method (Riesner et al., 2017). This resulted in reproducible fault representations that are more precise and often more segmented and interconnected than in previous model versions. The CFM 6.1 was peer reviewed and includes preferred representations for each fault system, along with alternative fault representations for which significant differences in subsurface structure have been proposed. Based on the earthquake-to-fault association method of Evans et al. (2020), the fault representations in CFM 6.1 show a 5.8% increased association with regional seismicity compared to CFM 5.2, with 89.7% of M 3 and larger events most likely associated with a CFM 6.1 fault. The faults also show a much higher degree of interconnectivity than in previous model versions, which will have implications for the assessment of potential earthquake ruptures involving multiple, distinct faults. The model is documented and distributed through a new website with a map and 3D views to facilitate broad usage with a wide range of applications in seismology, tectonic geodesy, computational modeling, and probabilistic and deterministic seismic hazard assessment.

Abstract This study examines how fault dip and sediment strength influence along-strike variability in patterns of ground surface deformation during thrust and reverse fault earthquakes. Expanding on the 2D distinct element method (DEM) analysis by Chiama et al. (2023) and Chiama, Bednarz, et al. (2025), we develop 3D DEM models to investigate the influence of along-strike variability of geological site parameters on resultant morphologies of coseismic ruptures. The main fault scarp types—monoclinal, pressure ridge, and simple—are successfully reproduced in these 3D models, aligning with surface rupture characteristics previously identified in 2D modeling. Uniform fault dips and homogeneous sediment properties produce symmetrical (or cylindrical) fault scarps with uniform scarp morphologies, whereas local variations in fault dip, sediment strengths, and sediment thickness above the fault tip form a range of scarp geometries, deformation zone widths, and patterns of secondary fracturing. These 3D DEM models reproduce patterns of surface fault ruptures observed in natural settings. Overall, the 3D models support the relationships of ground surface deformation characteristics (scarp class, width, and height) with source and sediment properties established in the 2D DEM results of Chiama, Bednarz, et al. (2025). In addition, they provide new insights into how fault dip and sediment strength govern along-strike transitions in fault scarp morphology. In combination, the results of the 2D and 3D DEM model results can be used to infer patterns of surface ruptures based on local geological site conditions and fault characteristics.

We investigate the influence of earthquake source characteristics and geological site parameters on fault scarp morphologies for thrust and reverse fault earthquakes using geomechanical models. A total of 3434 distinct element method (DEM) model experiments were performed to evaluate the impact of the sediment depth, density, homogeneous and heterogeneous sediment strengths, fault dip, and the thickness of unruptured sediment above the fault tip on the resultant coseismic ground surface deformation for a thrust or reverse fault earthquake. A machine learning model based on computer vision (CV) was applied to obtain measurements of ground surface deformation characteristics (scarp height, uplift, deformation zone width, and scarp dip) from a total of 346,834 DEM model stages taken every 0.05 m of slip. The DEM dataset exhibits a broad range of scarp behaviors, generating monoclinal, pressure ridge, and simple scarps—each of which can be modified by hanging wall collapse. The parameters that had the most influence on surface rupture patterns are fault displacement, fault dip, sediment depth, and sediment strength. The DEM results comprehensively describe the range of historic surface rupture observations in the Fault Displacement Hazards Initiative (FDHI) dataset with improved relationships obtained by incorporating additional information about the earthquake size, fault geometry, and surface deformation style. We suggest that this DEM dataset can be used to supplement field data and help forecast patterns of ground surface deformation in future earthquakes given specific anticipated source and site characteristics.

Abstract We establish a comprehensive three-dimensional geometric and kinematic description of the Front Ranges in the Bow Valley–Kananaskis region of the Southern Canadian Rocky Mountains to rigorously evaluate and expand upon fundamental paradigms that define our understanding of thin-skinned fold- and- thrust belts. We employ a modern strike and dip data collection method based on high-resolution imagery and digital elevation models, verified by direct field observations, to analyze the structures and construct balanced and retrodeformable cross sections. This approach yields &amp;gt;10,000 new attitude measurements of bedding and faults that represent a more than tenfold increase in previously published maps of the region. These observations and our analysis support many of the fundamental conclusions of previous work, namely the imbricate structural style and general break-forward progression of thrusting. However, our analysis suggests a pervasive, multi-modal distribution of bed dips separated by axial surfaces or hinge zones in the backlimbs of thrust sheets as opposed to the previous hypothesis of listric backlimb geometries. Our data also show bedding and fault dips that are generally parallel. These observations, coupled with the geologic map patterns, motivate refinements to the interpretation of structural styles, geometry, and faulting sequence of the region, including the presence of multiple regional basal detachments over an ~950 m zone. Through sequentially restoring our sections, we calculate a total shortening of 67 (±17%) km and derive a kinematic history of the Front Ranges that involves a complex, episodic sequence of thrusting. Overall, these insights, coupled with applying our semi-automated geologic data collection methods have applications for investigating exposed fold- and- thrust belts worldwide.

&lt;p&gt;Included in the supplement are details of how we calculated the error for the data presented in our scatterplot, along with seven additional figures. One is additional examples of our binning and fold analysis procedure and the results on three cross sections (m–m′ [51.06467°N, 115.586°W], [51.08187°N, 115.554°W]), n–n′ [50.92633°N, 115.132°W], [50.94936°N, 115.089°W], and o–o′ [51.05612°N, 115.446°W], [51.09349°N, 115.377°W]); palimpsestic restorations of our regional cross sections; high-resolution plates of our compiled geologic maps and associated cross sections; a map of our study area highlighting the bounds of maps we used to create our compiled map; a map of our study area detailing the bounds of our various digital elevation models; an example of our dynamic binning process from the data shown in Figure 5; regional cross sections with strike and dip data projected from 1 km away; and a comparison between different data collection methods. The remotely acquired strike and dip data are available on StraboSpot (https://strabospot.org/). Any GIS files needed to construct any of our geologic map figures in this study are available by emailing the corresponding author.&lt;/p&gt;

&lt;p&gt;Included in the supplement are details of how we calculated the error for the data presented in our scatterplot, along with seven additional figures. One is additional examples of our binning and fold analysis procedure and the results on three cross sections (m–m′ [51.06467°N, 115.586°W], [51.08187°N, 115.554°W]), n–n′ [50.92633°N, 115.132°W], [50.94936°N, 115.089°W], and o–o′ [51.05612°N, 115.446°W], [51.09349°N, 115.377°W]); palimpsestic restorations of our regional cross sections; high-resolution plates of our compiled geologic maps and associated cross sections; a map of our study area highlighting the bounds of maps we used to create our compiled map; a map of our study area detailing the bounds of our various digital elevation models; an example of our dynamic binning process from the data shown in Figure 5; regional cross sections with strike and dip data projected from 1 km away; and a comparison between different data collection methods. The remotely acquired strike and dip data are available on StraboSpot (https://strabospot.org/). Any GIS files needed to construct any of our geologic map figures in this study are available by emailing the corresponding author.&lt;/p&gt;

The Medical Student was published from 1888-1921 by the students of Boston University School of Medicine.

Introduction The Statewide California Earthquake Center (SCEC) Community Fault Model (CFM) is an object-oriented, fully three-dimensional geometric representation of active faults in California and adjacent offshore basins. For each fault object, the CFM provides triangulated surface representations (t-surfs) in several resolutions, fault traces in several different file formats (shape files, GMT plain text, and GoogleEarth kml), and complete metadata including references used to constrain the surfaces. The CFM faults are defined based on available data including surface traces, seismicity, seismic reflection profiles, well data, geologic cross sections, and various other types of data and models. The CFM serves SCEC as a unified resource for physics-based fault systems modeling, strong ground-motion prediction, probabilistic seismic hazards assessment (e.g., the USGS National Seismic Hazard Model), and many other uses. Together with the Community Velocity Model (CVM-H 15.1.0), the CFM comprises SCEC's Unified Structural Representation of the Southern California crust and upper mantle (Shaw et al., 2015). Current Model Version: CFM 7.0 The current version of the SCEC CFM is version 7.0 (CFM 7.0), which builds on the previous CFM releases and serves as the latest update to Plesch et al. (2007). CFM 7.0 is a significant update as this is the first CFM to cover the entire state of California, spanning the Pacific-North American plate boundary from northern Mexico to the southern Cascadia subduction zone. This latest version has no changes to the southern California portion of the model, but now includes 113 new fault representations in central and northern California in the preferred model. These new central and northern California fault representations will undergo a community evaluation in 2024-2025, therefore, the central and northern California faults should be considered preliminary representations. CFM 7.0 contains three fully-documented sub models: preferred, ruptures, and alternatives. In total, CFM 7.0 comprises the following components: CFM 7.0 Preferred: A set of 556 fault objects that constitute the preferred set of active faults. These faults have attained preferred status based on past community evaluations or are new representations. CFM 7.0 Ruptures: A set of 13 fault objects assembled from the CFM 7.0 preferred model that ruptured during selected significant historic events. These are not earthquake source models, but are representations of the entire fault surfaces where a significant historic rupture occurred. This model is intended to indicate which CFM fault objects were involved with selected significant historic ruptures. CFM 7.0 Alternatives: A set of 39 alternative representations where structural differences have been proposed that could potentially significantly impact fault mechanics and associated seismic hazards. These alternative representations were selected based on community rankings following a comprehensive evaluation of the CFM that took place in May of 2022. Including all sub models, the CFM 7.0 incorporates 608 fully-documented fault objects. If you use the CFM, we would appreciate you citing both Plesch et al. (2007) and the DOI where the archive is stored. Directory Structure and Contents of the CFM Archive The CFM archive directory structure is as follows: doc/Documentation and metadata, which include an MS Excel spreadsheet with detailed metadata about each fault surface. Metadata for the preferred, rupture, and alternative models are provided in separate but otherwise identically formatted sheets within the file. All faults contain references to the works that helped to define the 3D fault surface geometry. More information about the metadata columns is provided in doc/README.txt obj/preferred/obj/ruptures/obj/alternatives/These directories contain the model components for the preferred, rupture, and alternative models, respectively. Each model contains an identical directory structure, which is described below using the preferred model as an example. obj/preferred/native/The CFM preferred fault surfaces in gocad tsurf format using the native mesh. The native mesh uses a variable mesh resolution. Smaller triangles generally indicate where a fault is well-constrained by data. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). obj/preferred/500m/The CFM preferred fault surfaces with a semi-regularized mesh of ~500m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). obj/preferred/1000m/The CFM preferred fault surfaces with a semi-regularized mesh of ~1000m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). obj/preferred/2000m/The CFM preferred fault surfaces with a semi-regularized mesh of ~2000m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). obj/preferred/traces/Fault traces and upper tip lines (for blind faults) of the CFM preferred faults. While the CFM is a 3D model, it is often useful to make map-based visualizations of the model. The traces and blind faults are provided in several different formats described below. obj/preferred/traces/gmt/Fault traces and blind faults in Generic Mapping Tools multiple segment file ASCII format (i.e., plain text). .lonLat - Longitude/Latitude coordinates (WGS84 datum) .utm - UTM zone 11 NAD27 datum (EPSG:26711) obj/preferred/traces/kml/Fault traces and blind faults in Google Earth .kml format (WGS84 datum). The kml files also contain selected metadata as attributes which can be imported into QGIS. When a fault trace is clicked on in the Google Earth interface, a mini-webpage with metadata information will pop up. obj/preferred/traces/shp/Fault traces and blind faults in GIS shapefile format (longitude/latitude coordinates, WGS84 datum). CFM Contributors The current and past versions of the CFM would not be possible without contributions from numerous SCEC community members. We would like to thank the following CFM contributors: Christine Benson, William Bryant, Sara Carena, Michele Cooke, James Dolan, Jessica Don, Gary Fuis, Eldon Gath, Russell Graymer, Judith Hubbard, Susanne Janecke, Sam Johnson, Yuval Levy, Lisa Grant Ludwig, Egill Hauksson, Thomas Jordan, Marc Kamerling, Keith Knudsen, Mark Legg, Scott Lindvall, Harold Magistrale, James Lienkaemper, Scott Marshall, Craig Nicholson, Nathan Niemi, Stu Nishenko, Michael Oskin, Sue Perry, George Planansky, Andreas Plesch, Thomas Rockwell, David Schwartz, John Shaw, Peter Shearer, Bob Simpson, Christopher Sorlien, M. Peter Süss, John Suppe, Jerry Treiman, Jeff Unruh, Janet Watt, Franklin Wolfe, Chris Wills, Robert Yeats, and every colleague that has participated in a CFM community evaluation. We could not make the CFM without this community effort. CFM Evaluators Before assembling CFM 6.0 and subsequently CFM 7.0, a team of SCEC colleagues participated in a rigorous evaluation of CFM 5.3 in April-May of 2022. This evaluation was open to the SCEC community and focused on 23 critical fault representations where different proposed interpretations have the potential to significantly affect seismic hazards. This evaluation resulted in 14 new fault representations in the CFM 6.0 preferred model. The lower ranked representations are now provided in the CFM alternatives. We would like to thank the following CFM evaluators for volunteering their time and expertise to this process: Sinan Akçiz, Sara Carena, Michele Cooke, Tim Dawson, Jessica Don, Austin Elliot, Erik Frost, Gary Fuis, Athanassios Ganas, Eldon Gath, Alex Hatem, Susanne Janecke, Marc Kamerling, Christodoulos Kyriakopoulos, Mark Legg, Karen Luttrell, Chris Madugo, Scott Marshall, Andrew Meigs, Craig Nicholson, Nate Onderdonk, Alba Rodríguez Padilla, Andreas Plesch, Kate Scharer, John Shaw, Chris Sorlien, Franklin Wolfe, Doug Yule, Judy Zachariasen.

We investigate the influence of earthquake source characteristics and geological site parameters on fault scarp morphologies for thrust and reverse fault earthquakes using geomechanical models. We performed a total of 3,434 distinct element method (DEM) model experiments to evaluate the impact of the sediment depth, density, homogeneous and heterogeneous sediment strengths, fault dip, and the thickness of unruptured sediment above the fault tip on the resultant ground surface deformation during a thrust or reverse fault earthquake. We used a computer vision (CV) model to obtain measurements of ground surface deformation characteristics (scarp height, uplift, deformation zone width, and scarp dip) from a total of 346,834 DEM model stages taken every 0.05 m of slip. The DEM dataset exhibits a broad range of scarp behaviors, including monoclinal, pressure ridge, and simple scarps – each of which can be modified by hanging wall collapse. The parameters that had the most influence on surface rupture patterns are fault displacement (i.e., anticipated earthquake magnitude), fault dip, sediment depth, and sediment strength. The DEM results comprehensively describe the range of historic surface rupture observations in the Fault Displacement Hazards Initiative (FDHI) dataset with improved relationships obtained by incorporating additional information about the earthquake size, fault geometry, and surface deformation style. We suggest that this DEM dataset can be used to supplement field data and help forecast patterns of ground surface deformation in future earthquakes given specific anticipated source and site characteristics.

This report describes the need and concept of a framework that describes and classifies methane emissions monitoring requirements, emissions sources and monitoring methods using a set of taxonomies. It is envisaged that this framework will be developed into a standard to help facilitate more reliable transfer of information between stakeholders internationally.

ABSTRACT We present a new, 3D representation of the Long Beach restraining bend system along the Newport–Inglewood fault (NIF), Los Angeles, California. The NIF is an active strike-slip system that cuts over 60 km through densely populated metropolitan Los Angeles and poses one of the greatest deterministic seismic hazards in the United States (California Division of Mines and Geology, 1988). Part of the NIF sourced the 1933 M 6.4 Long Beach earthquake, which claimed ∼120 lives and remains one of the deadliest events in California history (Barrows, 1974; Hauksson and Gross, 1991). The event is thought to have arrested at Signal Hill within the Long Beach restraining bend, which is formed by a left step in the NIF (Hough and Graves, 2020). Events that rupture through Signal Hill could generate larger (M ≈7) events that pose a significant hazard to urban Los Angeles. Our analysis integrates a diverse range of datasets, including over 4200 fault and horizon penetrations from 243 wells, 2D seismic reflection surveys, field maps, machine-learning-based tomography studies, and the U.S. Geological Survey QFaults surface traces. We show that the fault system in Long Beach has three main strike-slip segments connected by orthogonal reverse faults. The strike-slip faults are nonvertical and nonplanar, merge at depth, and extend through the seismogenic crust. The Long Beach restraining bend system presents numerous rupture pathways and arrest points that NIF earthquakes may follow. We apply a novel, map-based restoration to quantify how much total slip has passed through each of the fault segments. About 375 m of total slip is partitioned into the three main fault strands, including the Reservoir Hill fault (≈75 m), the Northeast Flank fault (≈120 m), and the Cherry Hill fault (≈209 m). This slip partitioning informs our understanding of the tendency of ruptures to involve different fault segments or arrest at specific junctures.

SUMMARY A theory for modelling the evolution of elastic moduli of grain packs under increasing pressure is combined with a method that accounts for the presence of fine-grained particles to develop a new conceptual framework for computing the seismic velocities of compacting sediments. The resulting formulation is then used to construct a seismic velocity model for California’s Central Valley. Specifically, a set of 44 sonic logs from the San Joaquin Valley are combined with soil textural data to derive the 3-D velocity variations in the province. An iterative quasi-Newton minimization algorithm that allows for bounded variables provided estimates of the nine free parameters in the model. The estimates low- and high-pressure exponents that resulted from the fit to the sonic log velocities are close to 1/2 and 1/3, respectively, values that are observed in laboratory experiments. Our results imply that the grain surfaces are sufficiently rough that there is little or no slip between grains. Thus, the deformation may be modelled using a strain energy function or free energy potential. The estimated Central Valley velocity model contains a 27 per cent increase in velocity from the surface to a depth of 700 m. Lateral variations of around 4 per cent occur within the layers of the model, a consequence of the textural heterogeneity within the subsurface.

We define the physical processes that control the style and distribution of ground surface ruptures on thrust and reverse faults during large magnitude earthquakes through an expansive suite of geomechanical models developed with the distinct element method (DEM). Our models are based on insights from analog sandbox fault experiments as well as coseismic ground surface ruptures in historic earthquakes. DEM effectively models the geologic processes of faulting at depth in cohesive rocks, as well as the granular mechanics of soil and sediment deformation in the shallow subsurface. We developed an initial suite of 45 2D DEM experiments on dense, 5.0 m thick sediment in a model 50 m wide with a fault positioned 20 m from the driving wall and slipped each model at a constant rate (0.3 m/s) from 0 to 5.0 m. We evaluated a range of homogeneous sediment mechanics (cohesion and tensile strength from 0.1 to 2.0 MPa) across a range of fault dip angles. In addition, we examined various depths of sediment above the fault tip. Based on these experiments, we developed a classification system of the observed fault scarp morphology including three main types (monoclinal, pressure ridge, and simple scarps), each of which can be subsequently modified by hanging wall collapse. After this initial suite of models, we generated an additional 2,981 experiments of homogeneous and heterogeneous sediment in dense, medium-dense, and loosely packed sediment across a wide range of sediment depths and mechanics, as well as a range of fault dips (20 – 70º). These models provide robust statistical relationships between model parameters such as the fault dip and sediment strength mechanics with the observed surface deformation characteristics, including scarp height, width, and dip as well as the tendency for secondary fault splays. These relationships are supported by natural rupture patterns from recent and paleo-earthquakes across a range of geologic settings. In conjunction with these natural examples, our models provide a basis to more accurately forecast ground surface deformation characteristics that will result from future earthquakes based on limited information about the earthquake source and local sediment properties.

<strong>Introduction</strong> The SCEC Community Fault Model (CFM) is an object-oriented, three-dimensional representation of active faults in southern California and adjacent offshore basins. For each fault object, the CFM provides triangulated surface representations (t-surfs) in several resolutions, fault traces in several different file formats (shape files, GMT plain text, and GoogleEarth kml), and complete metadata including references used to constrain the surfaces. The CFM faults are defined based on all available data including surface traces, seismicity, seismic reflection profiles, well data, geologic cross sections, and various other types of data and models. The CFM serves the Southern California Earthquake Center (SCEC) as a unified resource for physics-based fault systems modeling, strong ground-motion prediction, and probabilistic seismic hazards assessment (e.g., UCERF3). Together with the Community Velocity Model (CVM-H 15.1.0), the CFM comprises SCEC's Unified Structural Representation of the Southern California crust and upper mantle (Shaw et al., 2015). <strong>Current Model Version: CFM6.1</strong> The current version of the SCEC Community Fault Model version 6.1 (CFM6.1) and is partially the result of a community evaluation of CFM5.3. CFM6.1 serves as the latest update to Plesch et al. (2007) and builds on previous CFM releases. New to CFM6.1 are two additional separate and fully-documented sub models: the ruptures and alternatives model. In total, CFM6.1 comprises the following components: The CFM6.1 Preferred Model: a set of 443 fault objects that constitute the preferred set of active faults in southern California. The CFM6.1 Rupture Model: a set of 13 fault objects assembled from the CFM6.1 preferred model that ruptured during selected significant historic events. These are not earthquake source models, but are representations of the entire fault surfaces where a significant historic rupture occurred. This model is intended to indicate which CFM fault objects were involved with selected significant historic ruptures. The CFM6.1 Alternatives: a set of 38 alternative representations where structural differences have been proposed that could potentially significantly impact fault mechanics and associated seismic hazards. These alternative representations were selected based on community rankings following a comprehensive evaluation of the CFM that took place in May of 2022. Including all sub models, the CFM6.1 incorporates 494 fully-documented objects. If you use the CFM, we would appreciate you citing the DOI where the archive is stored. <strong>CFM6.1 Change Log</strong> CFM6.1 differs from CFM6.0 in several ways, as described below. The Southern San Andreas fault was updated to the dipping model based on Fuis et al., (2012) which also contains a portion of the Banning fault. SAFS-SAFZ-MULT-Southern_San_Andreas_fault_and_Banning-CFM6 is now the preferred representation. Naming of this object is challenging because this object contains both what is typically referred to as the Southern San Andreas fault and a portion of the Banning fault. This is included in the metadata comments. SAFS-SAFZ-COAV-Southern_San_Andreas_fault-CFM4 (Steeply dipping) is now an alternative representation, SAFS-SAFZ-COAV-Southern_San_Andreas_fault-ALT6. The East Shoreline fault has been shortened to not extend north of Mecca Hills. SAFS-SAFZ-COAV-East_Shoreline_fault-CFM6 is the preferred version (same name in CFM6.0) and now no longer extends north of Mecca Hills. This is consistent with Janecke et al. (2019) where north of Mecca Hills the fault presence and location is mapped as speculative. The longer SAFS-SAFZ-COAV-East_Shoreline_fault-CFM5 is now provided as an alternative, SAFS-SAFZ-COAV-East_Shoreline_fault-ALT6. The Malibu Coast fault (east segment) has been truncated and merges with the Malibu Coast fault (west segment) and no longer extends farther to the west. The object name, WTRA-SFFS-SMMT-Malibu_Coast_fault_east-CFM6, remains the same. <strong>Directory Structure and Contents of the CFM6 Archive</strong> The archive directory structure is as follows: <strong>doc/</strong><br> Documentation and metadata, which include an MS Excel spreadsheet with detailed metadata about each fault surface. Metadata for the preferred, rupture, and alternative models are provided in separate but otherwise identically formatted sheets within the file. All faults contain references to the works that helped to define the 3D fault surface geometry. More information about the metadata columns is provided in doc/README.txt <strong>obj/preferred/<br> obj/ruptures/<br> obj/alternatives/</strong><br> These directories contain the model components for the preferred, rupture, and alternative models, respectively. Each model contains an identical directory structure, which is described below using the preferred model as an example. <strong>obj/preferred/native/</strong><br> The CFM6.1 preferred fault surfaces in gocad tsurf format using the native mesh. The native mesh uses a variable mesh resolution. Smaller triangles generally indicate where a fault is well-constrained by data. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/500m/</strong><br> The CFM6.1 preferred fault surfaces with a semi-regularized mesh of ~500m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/1000m/</strong><br> The CFM6.1 preferred fault surfaces with a semi-regularized mesh of ~1000m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/2000m/</strong><br> The CFM6.1 preferred fault surfaces with a semi-regularized mesh of ~2000m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/traces/</strong><br> Fault traces and upper tip lines (for blind faults) of the CFM6.1 preferred faults. While the CFM6.1 is a 3D model, it is often useful to make map-based visualizations of the model. The traces and blind faults are provided in several different formats described below. <strong>obj/preferred/traces/gmt/</strong><br> Fault traces and blind faults in Generic Mapping Tools multisegment ASCII format (i.e., plain text). .lonLat - Longitude/Latitude coordinates (WGS84 datum)<br> .utm - UTM zone 11 NAD27 datum (EPSG:26711) <strong>obj/preferred/traces/kml/</strong><br> Fault traces and blind faults in Google Earth .kml format (WGS84 datum). The kml files also contain selected metadata, which pops up if a fault is clicked on in the Google Earth interface. <strong>obj/preferred/traces/shp/</strong><br> Fault traces and blind faults in GIS shapefile format. Longitude/Latitude coordinates (WGS84 datum). <strong>CFM Contributors</strong> The current and past versions of the CFM would not be possible without contributions from numerous SCEC community members. We would like to thank the following CFM contributors: Christine Benson, William Bryant, Sara Carena, Michele Cooke, James Dolan, Jessica Don, Gary Fuis, Eldon Gath, Judith Hubbard, Susanne Janecke, Yuval Levy, Lisa Grant Ludwig, Egill Hauksson, Thomas Jordan, Marc Kamerling, Mark Legg, Scott Lindvall, Harold Magistrale, Scott Marshall, Jonathan Matti, Craig Nicholson, Nathan Niemi, Michael Oskin, Sue Perry, George Planansky, Andreas Plesch, Thomas Rockwell, John Shaw, Peter Shearer, Christopher Sorlien, M. Peter Süss, John Suppe, Jerry Treiman, Franklin Wolfe, Robert Yeats, and every colleague that has participated in a CFM community evaluation. We could not make the CFM without this community effort. <strong>CFM Evaluators</strong> Before assembling CFM6.1, a team of SCEC colleagues participated in a rigorous evaluation of CFM5.3 in April-May of 2022. This evaluation was open to the SCEC community and focused on 23 critical fault representations where different proposed interpretations have the potential to significantly affect seismic hazards. This evaluation resulted in 14 new fault representations in the CFM6.1 preferred model. The lower ranked representations are now provided in the CFM6.1 alternative model. We would like to thank the following CFM evaluators for volunteering their time and expertise to this process: Sinan Akçiz, Sara Carena, Michele Cooke, Tim Dawson, Jessica Don, Austin Elliot, Erik Frost, Gary Fuis, Athanassios Ganas, Eldon Gath, Alex Hatem, Susanne Janecke, Marc Kamerling, Christodoulos Kyriakopoulos, Mark Legg, Karen Luttrell, Chris Madugo, Scott Marshall, Andrew Meigs, Craig Nicholson, Nate Onderdonk, Alba Rodríguez Padilla, Andreas Plesch, Kate Scharer, John Shaw, Chris Sorlien, Franklin Wolfe, Doug Yule, Judy Zachariasen. <strong>References</strong> ● Evans, W. S., Plesch, A., Shaw, J. H., Pillai, N. L., Yu, E., Meier, M., &amp; Hauksson, E. (2020). A Statistical Method for Associating Earthquakes with Their Source Faults in Southern California. Bulletin of the Seismological Society of America, 110(1), 213-225. doi: 10.1785/0120190115. SCEC Contribution 9057 ● Hauksson, E., Yang, W., and Shearer, P. M., "Waveform Relocated Earthquake Catalog for Southern California (1981 to 2011)"; Bull. Seismol. Soc. Am., Vol. 102, No. 5, pp.2239-2244, October 2012, doi: 10.1785/0120120010 SCEC Contribution 1528 ● Plesch, A., et al. (2007). "Community Fault Model (CFM) for Southern California." Bulletin of the Seismological Society of America 97: 1793-1802. SCEC Contribution 1134 ● Plesch, A., Marshall, S. T., Nicholson, C., Shaw, J. H., Maechling, P. J., &amp; Su, M. (2020, 08). The Community Fault Model version 5.3 and new web-based tools. Poster Presentation at 2020 SCEC Annual Meeting. SCEC Contribution 10547 ● Shaw, J. H., Plesch, A., Tape, C., Suess, M., Jordan, T. H., Ely, G., Hauksson, E., Tromp, J., Tanimoto, T., Graves, R., Olsen, K., Nicholson, C., Maechling, P. J., Rivero, C., Lovely, P

ABSTRACT We seek to improve our understanding of the physical processes that control the style, distribution, and intensity of ground surface ruptures on thrust and reverse faults during large earthquakes. Our study combines insights from coseismic ground surface ruptures in historic earthquakes and patterns of deformation in analog sandbox fault experiments to inform the development of a suite of geomechanical models based on the distinct element method (DEM). We explore how model parameters related to fault geometry and sediment properties control ground deformation characteristics such as scarp height, width, dip, and patterns of secondary folding and fracturing. DEM is well suited to this investigation because it can effectively model the geologic processes of faulting at depth in cohesive rocks, as well as the granular mechanics of soil and sediment deformation in the shallow subsurface. Our results show that localized fault scarps are most prominent in cases with strong sediment on steeply dipping faults, whereas broader deformation is prominent in weaker sediment on shallowly dipping faults. Based on insights from 45 experiments, the key parameters that influence scarp morphology include the amount of accumulated slip on a fault, the fault dip, and the sediment strength. We propose a fault scarp classification system that describes the general patterns of surface deformation observed in natural settings and reproduced in our models, including monoclinal, pressure ridge, and simple scarps. Each fault scarp type is often modified by hanging-wall collapse. These results can help to guide both deterministic and probabilistic assessment in fault displacement hazard analysis.

<strong>Introduction</strong> The SCEC Community Fault Model (CFM) is an object-oriented, three-dimensional representation of active faults in southern California and adjacent offshore basins. For each fault object, the CFM provides triangulated surface representations (t-surfs) in several resolutions, fault traces in several different file formats (shape files, GMT plain text, and GoogleEarth kml), and complete metadata including references used to constrain the surfaces. The CFM faults are defined based on all available data including surface traces, seismicity, seismic reflection profiles, well data, geologic cross sections, and various other types of data and models. The CFM serves the Southern California Earthquake Center (SCEC) as a unified resource for physics-based fault systems modeling, strong ground-motion prediction, and probabilistic seismic hazards assessment (e.g., UCERF3). Together with the Community Velocity Model (CVM-H 15.1.0), the CFM comprises SCEC's Unified Structural Representation of the Southern California crust and upper mantle (Shaw et al., 2015). <strong>Current Model Version: CFM6.0</strong> The current version of the SCEC Community Fault Model version 6.0 (CFM6.0) and is partially the result of a community evaluation of CFM5.3. CFM6.0 serves as the latest update to Plesch et al. (2007) and builds on previous CFM releases. New to CFM6.0 are two additional separate and fully-documented sub models: the ruptures and alternatives model. In total, CFM6.0 comprises the following components: The CFM6.0 Preferred Model: a set of 443 fault objects that constitute the preferred set of active faults in southern California. The CFM6.0 Rupture Model: a set of 13 fault objects assembled from the CFM6.0 preferred model that ruptured during selected significant historic events. These are not earthquake source models, but are representations of the entire fault surfaces where a significant historic rupture occurred. This model is intended to indicate which CFM fault objects were involved with selected significant historic ruptures. The CFM6.0 Alternatives: a set of 36 alternative representations where structural differences have been proposed that could potentially significantly impact fault mechanics and associated seismic hazards. These alternative representations were selected based on community rankings following a comprehensive evaluation of the CFM that took place in May of 2022. Including all sub models, the CFM6.0 incorporates 492 fully-documented objects. If you use the CFM, we would appreciate you citing the DOI where the archive is stored. <strong>Directory Structure and Contents of the CFM6 Archive</strong> The archive directory structure is as follows: <strong>doc/</strong><br> Documentation and metadata, which include an MS Excel spreadsheet with detailed metadata about each fault surface. Metadata for the preferred, rupture, and alternative models are provided in separate but otherwise identically formatted sheets within the file. All faults contain references to the works that helped to define the 3D fault surface geometry. More information about the metadata columns is provided in doc/README.txt <strong>obj/preferred/<br> obj/ruptures/<br> obj/alternatives/</strong><br> These directories contain the model components for the preferred, rupture, and alternative models, respectively. Each model contains an identical directory structure, which is described below using the preferred model as an example. <strong>obj/preferred/native/</strong><br> The CFM6.0 preferred fault surfaces in gocad tsurf format using the native mesh. The native mesh uses a variable mesh resolution. Smaller triangles generally indicate where a fault is well-constrained by data. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/500m/</strong><br> The CFM6.0 preferred fault surfaces with a semi-regularized mesh of ~500m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/1000m/</strong><br> The CFM6.0 preferred fault surfaces with a semi-regularized mesh of ~1000m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/2000m/</strong><br> The CFM6.0 preferred fault surfaces with a semi-regularized mesh of ~2000m resolution in gocad tsurf format. All tsurf files are provided in UTM zone 11 using the NAD27 datum (EPSG:26711). <strong>obj/preferred/traces/</strong><br> Fault traces and upper tip lines (for blind faults) of the CFM6.0 preferred faults. While the CFM6.0 is a 3D model, it is often useful to make map-based visualizations of the model. The traces and blind faults are provided in several different formats described below. <strong>obj/preferred/traces/gmt/</strong><br> Fault traces and blind faults in Generic Mapping Tools multisegment ASCII format (i.e., plain text). .lonLat - Longitude/Latitude coordinates (WGS84 datum)<br> .utm - UTM zone 11 NAD27 datum (EPSG:26711) <strong>obj/preferred/traces/kml/</strong><br> Fault traces and blind faults in Google Earth .kml format (WGS84 datum). The kml files also contain selected metadata, which pops up if a fault is clicked on in the Google Earth interface. <strong>obj/preferred/traces/shp/</strong><br> Fault traces and blind faults in GIS shapefile format. Longitude/Latitude coordinates (WGS84 datum). <strong>CFM Contributors</strong> The current and past versions of the CFM would not be possible without contributions from numerous SCEC community members. We would like to thank the following CFM contributors: Christine Benson, William Bryant, Sara Carena, Michele Cooke, James Dolan, Jessica Don, Gary Fuis, Eldon Gath, Judith Hubbard, Susanne Janecke, Yuval Levy, Lisa Grant Ludwig, Egill Hauksson, Thomas Jordan, Marc Kamerling, Mark Legg, Scott Lindvall, Harold Magistrale, Scott Marshall, Jonathan Matti, Craig Nicholson, Nathan Niemi, Michael Oskin, Sue Perry, George Planansky, Andreas Plesch, Thomas Rockwell, John Shaw, Peter Shearer, Christopher Sorlien, M. Peter Süss, John Suppe, Jerry Treiman, Franklin Wolfe, Robert Yeats, and every colleague that has participated in a CFM community evaluation. We could not make the CFM without this community effort. <strong>CFM Evaluators</strong> Before assembling CFM6.0, a team of SCEC colleagues participated in a rigorous evaluation of CFM5.3 in April-May of 2022. This evaluation was open to the SCEC community and focused on 23 critical fault representations where different proposed interpretations have the potential to significantly affect seismic hazards. This evaluation resulted in 14 new fault representations in the CFM6.0 preferred model. The lower ranked representations are now provided in the CFM6.0 alternative model. We would like to thank the following CFM evaluators for volunteering their time and expertise to this process: Sinan Akçiz, Sara Carena, Michele Cooke, Tim Dawson, Jessica Don, Austin Elliot, Erik Frost, Gary Fuis, Athanassios Ganas, Eldon Gath, Alex Hatem, Susanne Janecke, Marc Kamerling, Christodoulos Kyriakopoulos, Mark Legg, Karen Luttrell, Chris Madugo, Scott Marshall, Andrew Meigs, Craig Nicholson, Nate Onderdonk, Alba Rodríguez Padilla, Andreas Plesch, Kate Scharer, John Shaw, Chris Sorlien, Franklin Wolfe, Doug Yule, Judy Zachariasen. <strong>References</strong> ● Evans, W. S., Plesch, A., Shaw, J. H., Pillai, N. L., Yu, E., Meier, M., &amp; Hauksson, E. (2020). A Statistical Method for Associating Earthquakes with Their Source Faults in Southern California. Bulletin of the Seismological Society of America, 110(1), 213-225. doi: 10.1785/0120190115. SCEC Contribution 9057 ● Hauksson, E., Yang, W., and Shearer, P. M., "Waveform Relocated Earthquake Catalog for Southern California (1981 to 2011)"; Bull. Seismol. Soc. Am., Vol. 102, No. 5, pp.2239-2244, October 2012, doi: 10.1785/0120120010 SCEC Contribution 1528 ● Plesch, A., et al. (2007). "Community Fault Model (CFM) for Southern California." Bulletin of the Seismological Society of America 97: 1793-1802. SCEC Contribution 1134 ● Plesch, A., Marshall, S. T., Nicholson, C., Shaw, J. H., Maechling, P. J., &amp; Su, M. (2020, 08). The Community Fault Model version 5.3 and new web-based tools. Poster Presentation at 2020 SCEC Annual Meeting. SCEC Contribution 10547 ● Shaw, J. H., Plesch, A., Tape, C., Suess, M., Jordan, T. H., Ely, G., Hauksson, E., Tromp, J., Tanimoto, T., Graves, R., Olsen, K., Nicholson, C., Maechling, P. J., Rivero, C., Lovely, P., Brankman, C. M., &amp; Munster, J. (2015). Unified Structural Representation of the southern California crust and upper mantle. Earth and Planetary Science Letters, 415, 1-15. doi: 10.1016/j.epsl.2015.01.016. SCEC Contribution 2068