Static Stress Changes due to the 1994 M6.7 Northridge Earthquake and the Potential for Triggered Slip on the San Andreas Fault
Abstract
The 1994 M6.7 Northridge earthquake occurred on a blind thrust fault located approximately 40 km south-southwest of the San Andreas fault in densely populated suburban Los Angeles. Savage and Svarc [2010] recently proposed that the Northridge earthquake may have triggered deep aseismic slip on the San Andreas fault. To test this hypothesis, we present results from three-dimensional kinematic and mechanical models of the Northridge event. We derive a coseismic slip distribution from a kinematic slip inversion of interferograms formed using data from the European Space Agency satellite ERS-1. For the Northridge thrust geometry, we use a triangular fault element mesh based on the SCEC Community Fault Model. This slip model is then incorporated into a mechanical model where we calculate the changes in static stresses on the San Andreas fault surface due to the Northridge coseismic slip. Analysis of the static Coulomb stress changes on the locked San Andreas fault suggest that part of the San Andreas fault was brought closer to failure by the Northridge event. The mechanical model results suggest that the increases in Coulomb stress on the San Andreas fault are dominantly due to unclamping, but spatially-varying directions of shear stress are predicted indicating that right lateral slip would be inhibited to the northwest, and promoted to the southeast. To determine a rough estimate of the magnitudes and directions of possible triggered aseismic slip on the San Andreas fault, we create a second mechanical model where the upper ten kilometers of the San Andreas are locked while the deep portions of the fault are permitted to slip freely in the strike-slip direction. We find that if the San Andreas did undergo triggered slip due to the Northridge event, portions of the SAF may have undergone contemporaneous right- and left-lateral slip. The model-predicted surface displacements from the triggered slip are compared to the postseismic GPS velocities of Savage and Svarc [2010].
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.S13A2246I
- Keywords:
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- 1242 GEODESY AND GRAVITY / Seismic cycle related deformations;
- 7223 SEISMOLOGY / Earthquake interaction;
- forecasting;
- and prediction;
- 8118 TECTONOPHYSICS / Dynamics and mechanics of faulting