3D modeling of ground rupture in thrust and reverse fault earthquakes: a distinct element approach

Kristen Chiama, Andreas Plesch, & John H. Shaw

Submitted September 7, 2025, SCEC Contribution #14470, 2025 SCEC Annual Meeting Poster #106

Thrust and reverse fault scarps that form during large earthquakes often feature complex patterns of distributed folding, fracturing, and uplift in surface fault ruptures that can vary significantly along-strike. We aim to evaluate the influence of fault parameters (slip, dip) and sediment strength mechanics on the patterns of ground surface deformation. We produced 80 3D distinct element method (DEM) models across 4 case studies: 1, planar faults with constant fault dip (20º, 40º, 60º); 2, variable fault dip along-strike from 20º to 70º; 3, variable depth of the fault tip; 4, amount of obliquity in fault slip. Across all of these cases, we tested homogeneous and heterogeneous sediment strengths by modifying the cohesion of the contact bonds using the parallel-bond contact model. We tested homogeneous sediment strengths including weak (1 MPa), moderate (3 MPa), and strong (5 MPa) sediment as well as heterogeneous sediment conditions with randomized heterogeneities along-strike and a cohesive top unit above loosely consolidated sediment.
Our results show that the most influential factor in determining the overall scarp type is the near-surface fault dip. Shallow faults produce pressure ridge scarps while steep faults produce monoclinal or simple scarps (consistent with Chiama et al., 2023, 2025). In parallel, the sediment strength determines the localization of slip in the near surface and differentiates the formation of monoclinal and simple scarps. The models with fault dip variability have the most diversity in scarp types present, while the randomized heterogeneity in sediment strength and depth of the fault tip produces the variability in surface deformation characteristics (scarp height, deformation zone width, scarp dip) within the given scarp type. Thus, the fault dip and along-strike variability in sediment strengths both contribute to significant along-strike variability in fault scarp morphology. We propose that insights from these 3D DEM models can help inform local site assessments for seismic hazards and aid in the community efforts for Probabilistic Fault Displacement Hazard Assessments (PFDHA).

Key Words
Thrust fault, Reverse fault, Tectonic Geomorphology, Distinct Element Method

Citation
Chiama, K., Plesch, A., & Shaw, J. H. (2025, 09). 3D modeling of ground rupture in thrust and reverse fault earthquakes: a distinct element approach. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology