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SAF_Stress_Evolution_1600_2020_SmithKonteretal.mp4 (1.42 MB)

San Andreas Fault System Stress Evolution (1600-2020)

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posted on 2020-09-10, 01:57 authored by Bridget Smith-KonterBridget Smith-Konter, L. Burkhard, Lauren WardLauren Ward, Paul WesselPaul Wessel, X. Xu, D.T. Sandwell
400-year earthquake cycle stress evolution simulation of the San Andreas Fault System. This simulation demonstrates the levels of tectonic Coulomb stress that accumulate throughout the earthquake cycle. Coulomb stress accumulation is based on a geodetically-constrained interseismic stress accumulation rate model and stress changes from 100+ historical and prehistorical earthquake ruptures (~M>6.0) spanning the past 420 years from new paleoseismic constraints (Scharer and Streig, 2019). Color scale is saturated at 3 MPa to emphasize significant regions of accumulated stress at seismogenic depths. The model also assumes complete stress release following each prescribed earthquake.

The North American-Pacific plate boundary is modeled as a series of vertical connected faults embedded in an elastic plate overlying a viscoelastic half-space. The 4-dimensional model simulates interseismic strain accumulation, coseismic displacement, and post-seismic viscous relaxation of the mantle. Long-term slip rates (i.e. over many earthquake cycles) are constrained to match contemporary geodetic estimates of far-field slip. Deep slip along these faults drives the secular interseismic crustal block motions. The block boundaries are locked from the surface down to a variable locking depth, which is also tuned to match the present-day GNSS measurements. Apparent locking depths range between 0 and 26 km. Stress varies as a function of observation depth within the seismogenic zone; in this simulation, we calculate the representative stress at 1/2 of the local locking depth. Stress calculations are performed on a fault-segment by fault-segment basis, thus only the local fault contributes to the final stress result. Restraining bends, such as San Bernardino and Mojave segments, have higher normal stress and lower rates of Coulomb stress accumulation; releasing bends, such as the Brawley segment, have lower normal stress and higher rates of Coulomb stress accumulation. Kinks and bends in the fault produce small-scale stress variations, so we average along the fault to minimize artificial effect.

Funding

NASA Earth Surface and Interior Program (80NSSC19K1043)

Southern California Earthquake Center (18149)

National Science Foundation (EAR-1829371)

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