Dynamic Modeling of Coseismic Rupture on Partially-Creeping Strike-Slip Faults
Abstract
Partially creeping faults exhibit complex behavior in terms of which parts of the fault slip seismically versus aseismically; this complexity is both temporal and spatial. Several faults in California exhibit creep that is rapid enough to be detected geodetically using InSAR, GPS and near-field methods, such as theodolite measurements of alignment arrays. Such studies of the Hayward Fault in the San Francisco Bay Area suggest that it has a complex pattern of creeping and locked patches along strike and down dip. The spatial pattern of creeping versus locked zones may have as much of an effect on throughgoing rupture as the more general presence of creep does. We use the 3D finite element modeling code FaultMod to conduct single-cycle models of dynamic rupture on partially creeping strike slip faults, in order to determine whether coseismic rupture can propagate into creeping regions, and how the presence and distribution of creep affects the ability of rupture to propagate along strike. We implement a rate-state friction criterion, in which locked zones of the fault are represented by rate-weakening behavior, and creeping zones of the fault are assigned rate-strengthening properties. We model two simplified partial creep geometries: a locked patch at the base of a largely creeping fault (similar to what is inferred for the Hayward Fault), and a creeping patch at the surface of a predominantly locked fault (similar to what is inferred for the Rodgers Creek Fault). We find that, in the case of a locked patch within a creeping fault, rupture does not propagate more than a kilometer past the edges of the locked patch, regardless of the patch radius. The case of a creeping patch within a locked fault is more complicated. We find that the width of the locked areas around the creeping patch determine whether or not rupture is able to propagate around the creeping patch and along the full strike of the fault; if the width of locked zone between the edge of the creeping patch and the end of the fault is too narrow, rupture is arrested. Regardless of along strike extent, rupture is able to penetrate several kilometers into the creeping patch, or all the way through it in the case of smaller patch radii, though at a slower rate than in the locked parts of the fault. By imposing multiple creeping and locked patches on a realistically complex fault geometry, we expect to be able to estimate the spatial and temporal distribution of coseismic slip on a partially creeping fault. We believe that combining the results of such dynamic models with static models of interseismic and postseismic creep may allow us to extend our slip estimates to cover the full earthquake cycle.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.G23B0796L
- Keywords:
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- 7209 SEISMOLOGY Earthquake dynamics;
- 8118 TECTONOPHYSICS Dynamics and mechanics of faulting;
- 1242 GEODESY AND GRAVITY Seismic cycle related deformations;
- 0545 COMPUTATIONAL GEOPHYSICS Modeling