Investigating the effects of velocity contrasts on rupture propagation along branching faults: Implications for the junction between the Mission Creek, Banning and the Southern San Andreas fault

Evan O. Marschall, Nobuki Kame, & Roby Douilly

Published September 8, 2024, SCEC Contribution #13779, 2024 SCEC Annual Meeting Poster #129 (PDF)

Complex crustal faults can sometimes separate material with different elastic properties. Dissimilar media around faults, also referred to as bimaterial interface, has been shown to cause effects on the rupture process along vertical strike-slip faults. Some previous studies suggest that asymmetry in wave propagation across a bimaterial interface can introduce normal stress changes on the fault near the rupture front that can lead to asymmetric bilateral or unilateral propagation. Furthermore, a bimaterial interface can also lead to differences in strain release across a fault interface for a fixed stress drop. Considering the effects caused by bimaterial interface on rupture propagation, it is worth understanding whether these effects can impact throughgoing rupture across a geometric complexity. In Southern California there are at least two branch fault systems which are inferred to have significant velocity contrasts across them: the junction of the Mission Creek and Banning segments on the Southern San Andreas fault (SAF) and the branching of the Clark and Buckridge Segments of the Southern San Jacinto fault (SJF). In this work we use dynamic rupture simulations to investigate the effects of velocity contrasts on rupture propagation along branch faults and the implications they may have in southern California. We generate a suite of finite element meshes with tetrahedral elements for different planar fault geometries including for the SAF and SJF. We assign a zone of stiffer material (between 0 to 20%) to one side of the fault system, such that both the main and secondary fault separate dissimilar media. The results indicate the rupture is less likely to propagate onto the secondary segment as the material contrast increases if the main fault and secondary faults have the same sense of slip. If the faults have opposite senses of slip, we find that a larger material contrast promotes propagation on the secondary fault. This may be related to asymmetric strain release across the bimaterial interface, as well as decreased rupture speeds from the material contrast. This indicates the Clark segment could be favored over the Buckridge segment along the SJF. However, for the SAF geometry we test both homogenous on-fault stresses as well as a resolved regional stress based on the SCEC CSM and that for stress conditions, the Mission Creek segment is favored over the Banning segment, independent of the material contrast.

Key Words
branch faults, dynamic rupture, numerical modeling

Citation
Marschall, E. O., Kame, N., & Douilly, R. (2024, 09). Investigating the effects of velocity contrasts on rupture propagation along branching faults: Implications for the junction between the Mission Creek, Banning and the Southern San Andreas fault. Poster Presentation at 2024 SCEC Annual Meeting.

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