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Group A, Poster #255, San Andreas Fault System (SAFS)

Large Events on the Southern San Andreas Fault Modulated by Lake Filling Events

Ryley Hill, Matthew Weingarten, Thomas K. Rockwell, & Yuri Fialko
Poster Image: 

Poster Presentation

2022 SCEC Annual Meeting, Poster #255, SCEC Contribution #12375 VIEW PDF
New geologic and paleoseismic data demonstrate that the past 6 major earthquakes on the Southern San Andreas Fault (SSAF) correlate with high-stands of the ancient Lake Cahuilla, a ~236 km3 body of water adjacent to the SSAF. To investigate the possible causal connections, we computed relative time-dependent Coulomb stress changes produced by lake level fluctuations over the last ~1100 years. Simulations were numerically solved using a fully coupled 3-D finite element model incorporating a poroelastic crust overlying a viscoelastic mantle. We find that the Coulomb stress perturbations on the SSAF are positive (i.e., promoting failure) throughout the lake loading history. For an acceptable ra...nge of material properties of the Earth's crust and well constrained lake ages, the estimated stress perturbations are of the order of 0.5 MPa, likely sufficient for triggering. Stress perturbations are dominated by pore pressure changes, but are enhanced by the poroelastic “memory" effect whereby increases in pore pressure due to previous lake high stands do not completely vanish by diffusion and constructively interfere with the undrained response in subsequent high stands. Our preferred model suggests that the lake loading modulated the interseismic stress accumulation on average by as much as 16-44%. The destabilizing effects of lake inundation are enhanced by a non-vertical fault dip, presence of a fault damage zone, and lateral pore pressure diffusion. Our results are applicable to other regions where hydrologic loading, either natural or anthropogenic, is associated with significant seismicity.