Comparing rupture behavior of the Mojave segment in two community fault models using a 3D fully dynamic earthquake simulator

Hasti Bordbar, Benchun Duan, Qingjun Meng, Zhi Shang, & Zizhuang Tang

Submitted September 7, 2025, SCEC Contribution #14755, 2025 SCEC Annual Meeting Poster #TBD

Understanding the influence of fault geometry on earthquake rupture propagation is critical for improving seismic hazard assessments in tectonically active regions. In this study, we employ EQdyna, a three-dimensional, fully dynamic earthquake simulator, to investigate the dynamic rupture behaviors of the southern San Andreas Fault (SSAF) over multiple earthquake cycles.
We compare two fault models derived from the SCEC Community Fault Model (CFM): one with nearly vertical dip angles (CFM version 5.3) and another with variable along-strike dip angles (CFM version 7). Which one is more realistic is still under debate. To explore the role of fault loading, we test two different initial stress conditions before the first cycle: (1) a simplified case with uniform along-strike normal stress; and (2) a more realistic case where a regional 3D stress tensor is resolved onto the fault surface using local strike and dip variations. We find that the former condition minimizes geometrical effects over earthquake cycles.
Rupture behavior of the Mojave segment differs markedly between the two fault models. In the near-vertical model, ruptures are more segmented and typically terminate near Elizabeth Lake (a paleoseismic site), consistent with paleoseismic observations of lower rupture frequency along the Mojave segment. In contrast, the variable-dip model facilitates more continuous and widespread ruptures through the Mojave segment, often terminating near Frazier Mountain (another paleoseismic site), as dip changes promote more favorable stress conditions for rupture propagation.
These findings underscore the crucial role of fault geometry in determining rupture extent, segmentation, and termination locations. Longer-term simulations are underway to determine better which fault model more closely reproduces the long-term rupture behavior of the SSAF, as revealed by paleoseismic studies.

Citation
Bordbar, H., Duan, B., Meng, Q., Shang, Z., & Tang, Z. (2025, 09). Comparing rupture behavior of the Mojave segment in two community fault models using a 3D fully dynamic earthquake simulator. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)