Session I :
Micro-physics underlying earthquake nucleation and frictional behavior of complex fault zones : observations and simulation

2nd ACES (APEC Cooperation for Earthquake Simulation) Workshop in Japan



Simulation of the Influence of Rate and State Dependent Friction on the Macroscopic Behavior of Complex Fault Zones with the Lattice Solid Model
Steffen Abe, James H. Dieterich, Peter Mora, David Place


Abstract

In order to understand the earthquake nucleation process, we need to understand the effective frictional behavior of faults with complex geometry and fault gouge zones. One important aspect of this is the interaction between the friction law governing the behavior of the fault on microscopic level and the resulting macroscopic behavior of the fault zone. Numerical simulations offer a possibility to investigate the behavior of faults on many different scales and thus provide a means to gain insight into fault zone dynamics on scales which are not accessible to laboratory experiments. The numerical experiments performed to investigate the influence of the rate and state friction on the dynamics of faults. These are designed to be similar to laboratory experiments by Dieterich and Kilgore in which a slide-hold-slide cycle was performed between two blocks of material and the resulting peak friction was plotted vs. holding time. Simulations with a flat fault without a fault gouge have been performed to verify the implementation. These have shown close agreement with comparable laboratory experiments. The simulations which have been performed with faults containing a fault gouge show a large dependence on the structure of the fault gouge. Simulations with a gouge in which the movement mainly takes place by grain rotation show a highly variable response to the holding event without a visible trend. Simulations with a gouge consisting of irrotational grains, however, show the expected increase in macroscopic friction. Preliminary results from those simulations also suggest that the macroscopic critical displacement Dc is dependent on the roughness of the fault surfaces.

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