Along-Strike Variability of Surface Deformation on Thrust and Reverse Fault Ruptures: Insights from 3D Distinct Element Method Models

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.