What is the effect of asymmetric topography on rupture propagation across the Cajon pass?
Abstract
Modeling the complexities of the fault system in southern California presents a series of challenges for numerical modelers. Significant examples of such complexities are the interconnected nature of the fault network (e.g. intersecting cross-faults), geometric discontinuities (branches and stepovers), the adjacency of major fault structures (e.g. San Andreas and San Jacinto faults), material heterogeneities, but also the intersection of the fault interface with the irregular topographic surface. This last feature and how specifically it affects fundamental values of rupture propagation (e.g. fault slip rate) is a topic that requires attention. In that perspective, a particular site of interest is the Cajon Pass in southern California. The southern San Andreas fault (SSAF) passes northwestwards through the Coachella valley and then cuts through the San Bernardino mountains and later through the San Gabriel mountains. The interesting "complication" here is that the two mountains are placed asymmetrically with respect to the fault trace. For that reason, south of the Cajon pass and before the Coachella valley (from SE to NW), the topographic dome is to the north of the fault, while north of the pass the topography is to the south. This particular setting generates an asymmetric topographic effect on the top of the fault interface. It is reasonable to ask how this asymmetry in the free surface effect will affect the rupture mechanism and eventually the possibility of a through-going rupture across the Cajon pass. For that reason, we generated a finite element mesh of southern California that includes the topographic features of the San Bernardino and San Gabriel mountains and the SSAF fault interface (based on UCERF3). We combine our mesh with the dynamic rupture code FaultMod (Barall, 2009) to investigate how the topographic asymmetry will eventually modulate a possible through-going rupture. We compare our preliminary results with a model that implements a flat free surface and therefore does not account for the topographic asymmetry.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S41D0568K
- Keywords:
-
- 4314 Mathematical and computer modeling;
- NATURAL HAZARDSDE: 7215 Earthquake source observations;
- SEISMOLOGYDE: 7221 Paleoseismology;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS