Schedule Oct 11, 2005
Quasidynamic Simulations of Long Deformation Histories on a Heterogeneous Fault
Dr. Gert Zöller, University of Potsdam

We attempt to develop a physical basis for earthquake dynamics and seismic hazard on large strike-slip faults by joint analysis of model realizations, with parameters representing specific fault zones, and multidisciplinary observations of deformation phenomena. The model consists of discrete slip patches (representing structural segmentation) on a vertical plane in a 3-D solid, and it accounts for brittle slip, creep slip, realistic boundary conditions, and 3-D elastic stress transfer. Recent developments extended the framework to incorporate quasidynamic rupture propagation, gradual healing, and creeping barriers along the fault.

We show that the model produces realistic frequency-size and temporal statistics of earthquakes, hypocenter distributions, foreshock-mainshock-aftershock sequences, slip histories, approach to and retreat from criticality, and accelerating seismic release. Systematic analytical and numerical parameter-space studies indicate the existence of basic dynamic regimes. The first is associated with strong fault heterogeneities, power law frequency-size statistics of earthquakes, and random or clustered temporal statistics of intermediate and large events. The second is associated with homogeneous or relatively regular faults, peaked frequency-size statistics (compatible with the characteristic earthquake distribution), and quasi-periodic temporal occurrence of large events. For a range of parameters, there is a third regime in which the response switches back and forth between the forgoing two modes of behavior. The results can be understood in terms of the phase diagram technique and the concept of intermittent criticality.

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