DATE:

Friday, February 18, 2022

TIME:

3:30 PM

LOCATION:

GMCS 314

SPEAKER:

Dr. Matthew Weingarten, Geological Sciences, San Diego State University

ABSTRACT:

Recent paleoseismic evidence shows that previous ruptures on the Southern San Andreas Fault (SSAF) correlate with high-stands of the ancient Lake Cahuilla, a √¢¬à¬º236 km^3 body of water adjacent to the SSAF. We investigate time-dependent Coulomb stress changes caused by high-stands of ancient Lake Cahuilla for the last √¢¬à¬º1100 years using a fully coupled 3D finite element model of a strike-slip fault in a poroelastic crust overlying a viscoelastic mantle. We find the Coulomb stress perturbations are positive √¢¬Ä¬ì enhancing the likelihood of SSAF rupture. Stress perturbations are on the order of 0.3-0.7 MPa for a plausible range of the fault damage zone permeabilities. The relatively high “hydrologic” stress perturbation is due in part to what we refer to as the “memory” effect whereby increases in pore pressure due to previous high stands do not completely vanish by diffusion and constructively interfere with the undrained response due to subsequent increases in the lake level. Our preferred model estimates that lake loading complemented the interseismic stress accumulation by 12-24.5% at the seismogenic depths during several previous earthquake cycles. Our model also indicates that the destabilizing effects of lake inundation are enhanced in the presence of a non-vertical fault dip, fault damage zone, and lateral pore pressure diffusion

HOST:

Christopher Paolini

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