The Influence of Fault-Dip Variations on Multicycle Earthquake Rupture Dynamics of the San Andreas Fault

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

Published September 8, 2024, SCEC Contribution #14005, 2024 SCEC Annual Meeting Poster #156

The Mojave section of the San Andreas Fault (SAF) offers a unique study area due to its relatively straight surface trace, which is bounded by the Big Bend to the north and the San Jacinto Fault (SJF) to the south, encompassing a southwest-dipping northern part, a vertical middle part, and a northeast-dipping southern part. Historical records highlight a discrepancy in seismic activity: the 1857 Fort Tejon earthquake ruptured through this section, whereas the 1812 event from the south halted midway. Recent paleoseismic studies indicate a lower earthquake frequency in the middle of the Mojave section than in adjacent sections.

This study explores the impact of fault-dip variations on earthquake rupture behavior along this section of the SAF over multiple earthquake cycles. We used the SCEC Community Fault Model (CFM) to develop a realistic model of dip-varying fault geometry and a reference model of vertical dipping fault geometry as a comparison. Using Coreform Cubic, we created finite element meshes. We employ a newly developed dynamic earthquake simulator based on the finite element method (FEM) EQdyna, which captures both quasi-static and fully dynamic processes, to perform 3D multicycle dynamic simulations for the two models. This simulator integrates rate- and state-dependent friction laws to model the full earthquake cycle.

The Comparison of rupture propagation between the two models reveals that the fault geometry with varying dip exhibits more complex rupture behavior than the vertical fault model. The dip changes along the strike-slip fault can act as a barrier, potentially terminating the rupture. This complexity is primarily driven by a nonlinear strike at the fault's base. These variations in rupture dynamics correspond with the observed seismic activity patterns, including the lower earthquake frequency in the central Mojave section.

Citation
Bordbar, H., Duan, B., Meng, Q., Shang, Z., & Tang, Z. (2024, 09). The Influence of Fault-Dip Variations on Multicycle Earthquake Rupture Dynamics of the San Andreas Fault. Poster Presentation at 2024 SCEC Annual Meeting.

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