An official website of the United States government
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.
more »
« less
This content will become publicly available on July 30, 2026
Quantifying relationships between fault parameters and rupture characteristics associated with thrust and reverse fault earthquakes
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.
more »
« less
- Award ID(s):
- 2207119
- PAR ID:
- 10644518
- Publisher / Repository:
- Sage Publisher
- Date Published:
- Journal Name:
- Earthquake Spectra
- ISSN:
- 8755-2930
- Subject(s) / Keyword(s):
- Earthquake rupture, ground surface deformation, tectonic geomorphology, distinct element method, DEM models, fault scarp
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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.more » « less
-
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.more » « less
-
Field observations of surface rupture extent and fault displacement are critical to improving our understanding of rupture processes in the 6 February 2023 earthquakes in the Kahramanmaraş region of Türkiye. This data release includes two primary datasets depicting the 2023 moment magnitude (Mw) 7.8 Pazarcık, Türkiye earthquake rupture: 1) surface rupture mapping (lines) and 2) measurements of left-lateral and vertical fault displacement (points). These observations were made in the field, northwest of Pazarcık, Türkiye along the East Anatolian (EAF) and Narlı faults between 2 and 11 June 2023. Surface-rupture mapping consists of field observations along a 28-km-long reach of the central EAF and northern 5 km of the Narlı fault that lacked previous remote observations. An additional dataset includes observations of no surface rupture. Displacement data include 68 field observations of left-laterally and vertically displaced natural or cultural features, with 62 measurements along the central EAF and 6 measurements on the Narlı fault. Collectively, these data support scientific and humanitarian response efforts, provide field observations for comparison to remote data, and help improve our understanding of the geologic context of the 2023 Kahramanmaraş region earthquakes. This database, identified as Field Observations of Surface Rupture and Fault Displacement in the 2023 Mw 7.8 Pazarcık, Türkiye Earthquake, has been approved for release by the U.S. Geological Survey (USGS). Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, the database is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Explanation of Data Surface Rupture Mapping Surface-rupture mapping consists of 18 km of on-the-ground field observations along a 28 km reach of the EAF and the northern 5 km of the Narlı fault recorded using handheld global navigation satellite system (GNSS) devices and tablets. Rupture traces were mapped at a spatial accuracy of ≤10 m and compiled in the office at a scale of 1:1500. Although these data accurately represent the rupture at this scale, additional distributed, cryptic, or small (<0.1 m) displacements not recognized in the field may be present but not depicted in the linework. Linework are available as shapefile, keyhole markup language, and geojson. Fields: Fault: Fault along which rupture observation was made. EAF – East Anatolian fault. Date: Calendar date of rupture mapping in format day–month-year. Notes: Notes on geomorphic expression of rupture. “Null” indicates no additional information reported for rupture trace. No Surface Rupture This dataset includes line observations of no surface rupture. These data represent areas that we walked during our field campaign, but made no observations of rupture, including distributed zones of cracking or displacement. Although we are confident that no surface rupture with measurable lateral or vertical displacement (exceeding a few centimeters) is present in this area, cryptic or subtle (<0.01 m) displacements not recognized in the field may be present but not depicted in the linework. Linework based on walk tracks mapped at a spatial accuracy of ≤10 m and simplified and compiled in the office at a consistent scale of 1:1500. Linework are available as shapefile, keyhole markup language, and geojson. Fields: Date: Calendar date of no rupture observation in format day–month-year. Notes: Notes on whether minor cracking, without measurable lateral or vertical displacement, was observed. Displacement data Fault displacement data include 68 field observations of left-laterally and vertically displaced natural (e.g., gully thalweg) or cultural (e.g., road edge) features along the EAF and Narlı fault. Left-lateral displacements were measured by projecting sub-linear features into the fault rupture using chaining pins and tape measures. Data were recorded using field notebooks, cameras, tablets, and handheld GNSS devices (≤10 m accuracy) and compiled in the office. Time-averaged GNSS points from tablets and high-precision GNSS (Trimble Geo7x; <1 m accuracy) measured along the features were recorded in the field and used in the office to measure displacement. Descriptions of measurement methods, features evaluated, and displacement values and uncertainties are included in tabular format as comma-separated values (CSV), shapefile, keyhole markup language, and geojson. Fields: ID: Unique numerical identifier for point observation. Latitude: Decimal degrees north of the equator; WGS 84, EPSG 4326. Longitude: Decimal degrees east of the prime meridian; WGS 84, EPSG 4326. Date. Calendar date of point measurement in format day–month-year. Fault: Fault along which displacement observation was made. EAF – East Anatolian fault. H_pref_m: Field-based preferred left-lateral displacement in meters of a natural (e.g., stream channel) or cultural (e.g., concrete wall) feature crossing the fault. Pref_type: Methods used to determine H_pref_m. Measured – value measured in the field. Sum – value is the sum of separate displacement measurements for subparallel strands (refer to Notes field for description and component displacement values). Midpoint – value is the midpoint between the H_min_m and H_max_m displacement values. Spatial – value measured in the office using spatial data (points) recorded in the field. H_min_m: Field-based minimum left-lateral displacement in meters of a natural or cultural feature crossing the fault. Approximates lower 95% confidence bound unless otherwise noted. H_max_m: Field-based maximum left-lateral displacement in meters of a natural (e.g., stream channel) or cultural (e.g., concrete wall) feature crossing the fault. Approximates upper 95% confidence bound unless otherwise noted. Aperture_m: Total distance over which features offset by fault rupture are projected to determine displacement across the site. The aperture includes the fault zone and any distributed deformation of the feature. FaultStrike: Local (m-scale) strike of fault in degrees at displacement measurement site using a 6-degree declination. Measurements without a corresponding dip entry (NaN entry in FaultDip field) reflect the general azimuth of the surface rupture with an estimated uncertainty of ±5 degrees. FaultDip: Local (m-scale) dip of fault in degrees at displacement measurement site. Dip direction is based on right-hand rule, combined with the corresponding FaultStrike entry for the measurement site. FeatAzim_N: Azimuth of the faulted cultural or natural feature in degrees (6-degree declination) on the north side of the surface rupture. FeatAzim_S: Azimuth of the faulted cultural or natural feature in degrees (6-degree declination) on the south side of the surface rupture. V_pref_m: Field-based preferred scarp height in meters of a natural or cultural feature or surface crossing the fault. V_min_m: Field-based minimum scarp height in meters of a natural or cultural crossing the fault. V_min_m approximates lower 95% confidence bound unless otherwise noted. V_max_m: Field-based maximum scarp height in meters of a natural or cultural feature or surface crossing the fault. Approximates upper 95% confidence bound unless otherwise noted. ScarpFaceDir: Facing direction of vertical scarp produced in surface rupture. Variable – variable scarp facing directions are present. None – rupture does not have a vertical expression. MsmtType: Whether left-lateral or vertical displacements capture slip in all known rupture traces. Complete – measurement captures all recognized and mapped slip at the site; however, the measurement may still lack minor displacement from distributed, far-field, and/or cryptic slip. Incomplete – Some recognized and mapped rupture traces are not accounted for in the displacement measurement (e.g., the feature evaluated only crosses one of two subparallel rupture strands) and is considered a minimum value. Likely complete – the measurement is more likely to be a complete measurement than an incomplete (minimum) estimate. Likely incomplete – the measurement is more likely to be an incomplete (minimum) estimate than a complete measurement. Setting: General setting of the displacement measurement. Cultural includes built (e.g., rock wall), planted (e.g., orchard rows), or modified (e.g., irrigation ditch) features. Natural indicates erosional or depositional features such as a gully or gravel bar. Feature: Natural or cultural feature crossing the fault, displaced by the surface rupture, and used to estimate left-lateral and/or vertical displacement. MsmtMethod: Methods used to measure horizontal displacement. Projection – natural or cultural feature projected into the fault zone using chaining pins and/or tape measures with uncertainty defined by multiple projections. Quick tape – displacement estimated by measuring the distance between piercing points (where linear features crossing the fault intersect the rupture) subparallel to the fault rupture with a tape measure (no projections). Uncertainties measured or estimated. Spatial – points along feature measured using time-averaged Trimble Geo7x or Avenza; displacement measured in office with uncertainties based on multiple projections. Notes: Description of the feature used to measure displacement, the expression of the rupture (e.g., multiple strands), measurement confidence, and/or information on repeated measurements. Abbreviations: EQ – earthquake; msmt – measurement; N – north; S – south; E – east; W – west; NE – northeast; NW – northwest; SE – southeast; SW – southwest; Geo7x – Trimble Geo7x GNSS device; GEER team – previous measurements made by a Geotechnical Extreme Events Reconnaissance (GEER) team in March 2023.more » « less
