Multi-cycle Dynamics of the San Andreas and San Jacinto Faults in Southern California

Dunyu Liu, & Benchun Duan

Published August 15, 2019, SCEC Contribution #9690, 2019 SCEC Annual Meeting Poster #144

Natural fault systems have geometric complexities at various scales. Earthquake ruptures may halt at or propagate through these complexities, especially macroscopic ones (so called ‘earthquake gates’), depending on fault geometries and fault stress/strength that vary with rupture histories. Therefore, earthquake gates may control total rupture lengths and thus earthquake sizes. The Cajon Pass and the Big bend are two major earthquake gates along the San Andreas Fault and the San Jacinto Fault in Southern California. In this study, we model 2D multicycle dynamics of the San Andreas Fault from Parkfield to the Salton Sea and the San Jacinto Fault (Claremont) with some simplifications and explore possible rupture scenarios over multiple earthquake cycles. The 2D simulation method consists of a finite element model for coseismic spontaneous ruptures and an analytic viscoelastic model for interseismic fault stress evolutions. We apply the maximum shearing direction parallel to the general strike of Parkfield and Cholame segments. Four types of representative events emerge in the model. They are 1) the large event rupturing the Parkfield and Cholame segments and a major portion of the Carrizo segment, 2) the large event rupturing the San Jacinto Fault, the Mojave segment, San Bernadino segment and part of the Indio segment, 3) the moderate event rupturing the San Jacinto Fault (not often), and 4) the small event breaking part of the Indio segment (rare). The type 2) event typically nucleates on the San Jacinto Fault where the strike aligns well with the maximum shearing direction. The rupture propagates bilaterally, and it jumps to the San Andreas Fault at the Cajon Pass. Then, the rupture breaks the Mojave and San Bernardino segments. The rupture on the San Jacinto Fault also jumps to the Indio segment at the location where the strike aligns well with the maximum shearing direction. These results provide physical insights into rupture behaviors of the Cajon Pass earthquake gate.

Key Words
Cajon Pass, Earthquake Multicycle Dynamics, Fault Geometric complexities,

Citation
Liu, D., & Duan, B. (2019, 08). Multi-cycle Dynamics of the San Andreas and San Jacinto Faults in Southern California. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)