Virtual California:
Interplay Between Fault System Complexity, Dynamics, and Numerical Stability
P. B. Rundle1, G. Morein, J. B. Rundle2, K. F. Tiampo3, A. Donnellan4 and D. L. Turcotte5
Virtual California is a topologically realistic simulation of the interacting earthquake faults in California. Inputs to the model arise from field data, and typically include realistic fault system topologies, realistic long term slip rates, and realistic frictional parameters. Outputs from the simulations include synthetic earthquake sequences and space-time patterns together with associated surface deformation and strain patterns that are similar to those seen in nature. It is a type of model called a backslip model, so called because the loading in the model arises from negative slip or “backslip” applied to each fault boundary element at its geologically observed long-term rate of offset, V(x). We note that in this context, a fault element is regarded simply as a “degree of freedom”, rather than a spatially coherent entity with geological meaning. All of the rectangular fault elements are embedded in an elastic half space, and they interact with each other by means of quasistatic elastic interactions, whose stress Greens functions are computed by means of a boundary element method. Frictional coefficients are assigned to each fault element, along with other frictional parameters, by means of a data assimilation technique. When the model is used to produce a simulation, the result is a history of slip on the fault elements in response to the driving forces. The interactions between the fault elements serve to organize the system so that, instead of a sequence of single elements breaking individually, multiple elements break simultaneously, producing large earthquakes. The dynamical evolution in the model is also produced by means of a stochastic, cellular automaton method, in which a random overshoot or undershoot component is added at the time of sliding of a element. The topology of the model fault system has evolved over time, becoming more complex, and using progressively finer scales of detail. Here we discuss the latest versions of the fault system topology and the associated numerical simulations. We focus in particular on the interplay between fault system complexity, and complexity in the dynamics. We find that the mesh scale of the boundary elements is strongly affected by the scale fault topology, and that the stability properties of the dynamics are likewise strongly affected.
1Center for Computational Science and Engineering and Departments of Physics and Engineering, University of California at Davis, Davis, CA, USA
2Center for Computational Science and Engineering and Departments of Physics and Engineering, University of California at Davis, Davis, CA, USA
3Department of Earth Sciences, University of Western Ontario, London, ON, Canada
4Earth and Space Science Division, Jet Propulsion Laboratory, Pasadena, CA, USA
5Department of Geology, University of California at Davis, Davis, CA, USA
