[Faculty] Fwd: [CSRC.COLLOQUIUM] "Coupled poroelastic modeling of an active plate boundary fault zone: was a lake responsible for past M7+ earthquakes on the Southern San Andreas Fault? "

[Jose Castillo]

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DATE:
*Friday, February 18, 2022*


TITLE:
*Coupled poroelastic modeling of an active plate boundary fault zone: was a
lake responsible for past M7+ earthquakes on the Southern San Andreas
Fault?   *

TIME:
*3:30-4:30PM*



LOCATION:
*In Person - GMCS 314*
or
Join Zoom Meeting -   https://SDSU.zoom.us/j/84471061245
<https://sdsu.zoom.us/j/84471061245>


SPEAKER/BIO:
*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 ∼236 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 ∼1100 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
– 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*

Note: Videos of previous colloquium talks can be seen on the CSRC website
in the colloquium archive section or on the CSRC YouTube page here
<https://www.youtube.com/channel/UCN0ZEztlmyDqG2pm-Rle_Eg/feed>.





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