Numerical Simulations for Earthquake Physics (Virtual California): Recent Results and Current Plans

Attention has recently been focused on the need for numerical simulations of interacting earthquake fault systems [1]. "Virtual California" is a topologically realistic model which has been used to simulate earthquakes on the San Andreas fault and its associated fault system. The Virtual California model includes elastic interactions among the faults in the model, driving at the correct plate tectonic rates, and frictional physics on the faults using the physics obtained from laboratory models with parameters consistent with the occurrence of historic earthquakes. An important consequence of the elastic interactions in the model is the appearance of correlations and space-time patterns of occurrence of events. Without the interactions, each fault element would behave independently; with the interactions, cooperative phenomena and patterns are observed. Previous numerical analysis of this simulation has focused on the distribution of recurrence times between large events. From this it is possible to compute the waiting times until the next great earthquake for California faults. Here we report on a variety of recent results. 1) We are investigating the stability of the numerical solutions and how these depend on the Greens function computations and other assumptions in the displacement discontinuity method; 2) We have developed a new method for generating and scoring a synthetic earthquake catalog utilizing Virtual California. The idea is to use paleoseismic data to identify intervals within the artificial data which most closely resemble the current seismic state of California; 3) We are working with collaborators to understand the interplay between fault system complexity and predictability. In this talk we summarize and discuss these issues, and indicate directions for the future.