SCEC Award Number 19238 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Multi-cycle dynamics of the San Andreas and San Jacinto faults in Southern California
Investigator(s)
Name Organization
Benchun Duan Texas A&M University
Other Participants
SCEC Priorities 1d, 2e, 5a SCEC Groups FARM, SAFS, CS
Report Due Date 04/30/2020 Date Report Submitted 04/30/2020
Project Abstract
 Dynamic rupture models on realistic fault geometries in the context of earthquake cycles is one of physics-based tools to assess seismic hazard on real fault systems. The Cajon Pass, which is the triple junction between the San Andreas and San Jacinto faults, and the Big Bend on the San Andreas fault are two prominent fault geometrical complexities, i.e., earthquake gates, that would influence rupture extents and magnitudes of earthquakes on the fault system. In this project, we explore multicycle dynamics of the San Andreas fault from Parkfield to Salton Sea and the San Jacinto Fault (Claremont segment) with our 2D numerical methods for earthquake cycles. The method consists of a finite element model for coseismic spontaneous ruptures and an analytic Maxwell viscoelastic model representing the tectonic loading, viscoelastic relaxation and off-fault deformation (Duan, 2019; Duan et al., 2019; Duan and Oglesby, 2005). We adopt realistic fault geometry from Community Fault Model 5.2 (Nicholson et al., 2017; Plesch et al., 2007) to build our models. The fault geometric complexity is the only heterogeneity we consider in models while we keep the shear loading uniform. The results show a variety of representative rupture scenarios that are comparable to paleoseismicty and may be indicative for future rupture scenarios, including ruptures that can jump over the Cajon Pass gate from the San Jacinto fault to the San Andreas fault.
Intellectual Merit This project models earthquake cycles, especially dynamic ruptures, on the San Andreas and the San Jacinto faults with realistic fault geometries from the well-developed Community Fault Models in Southern California. Earthquake sequences in the models are dictated by heterogeneous stresses developed over earthquake cycles. The rupture scenarios, which are comparable to paleoseismicty, show various rupture extents bounded by critical macroscopic fault geometrical complexities such as the Big Bend and the Cajon Pass triple junction. The integration of the physics-based models and paeloseismicity provides us with better information to assess seismic hazard on the San Andreas and San Jacinto faults in Southern California.
Broader Impacts The project supports a Postdoc researcher who is applying scientific programming and parallel computing to model earthquake source dynamics on geometrically realistic fault to assess seismic hazard. In addition, rich information in paleoseismological records such as the complexity in earthquake recurrence intervals and rupture extents help constrain numerical models and lend the models credibility to infer future rupture scenarios. With realistic fault geometries and dynamic ruptures modeled in the context of earthquake cycles, earthquake sequences in this study show features like rupture scenarios of various rupture extents and sizes, ruptures conditionally impeded by earthquake gates, long-term slip rate, complexities in earthquake recurrence intervals, etc. Such features would facilitate collaboration among modelers, paleoseismologists, and geologists to yield a more informed picture to assess probability of multiple-fault ruptures in earthquake-prone regions such as Southern California.
Exemplary Figure Figure 2. Representative rupture scenarios from the earthquake sequence simulated. (a) A super-large rupture that breaks the whole fault system, which shows potential like the 1857 Fort Tejon earthquake. (b) A large rupture that breaks the San Andreas segments northwest to the Big Bend. (c) A large rupture that breaks most of the San Andreas segments southeast to the Big Bend. (d-e) Moderate earthquakes occurring on the San Jacinto fault that are comparable to 1899, 1918, 1923 earthquakes. (f) A moderate earthquake that breaks the Indo segment. (g-h) Super-large ruptures that nucleate near the Cajon Pass and break the whole fault system, in which event h involves the rupture jumping from the San Jacinto fault over the Cajon Pass to the San Andreas fault.