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Stress Transfer in Earthquakes and Forecasting: Inferences from Numerical Simulations

John B. Rundle, Paul B. Rundle, Andrea Donnellan, William Klein, Gleb Morein, Peggy Li, & Donald L. Turcotte

In Preparation 2005, SCEC Contribution #777

Observations indicate that earthquake faults occur in topologically complex, multi-scale networks driven by plate tectonic forces. In this system, the true stress-strain dynamics is inaccessible to direct observations, or unobservable. Conversely, the space time patterns associated with the time, location, and magnitude of the earthquakes are easily observable. We are therefore developing realistic numerical simulations, involving data-mining, pattern recognition, theoretical analysis and ensemble forecasting techniques, to understand how the observable space-time earthquake patterns are related to the fundamentally inaccessible and unobservable dynamics. Numerical simulations can also help us to understand the different scales involved in earthquake physics interact and influence the resulting dynamics. For example, we can investigate how processes operating on time scales of seconds and spatial scales of meters, such as source process times in fault zones, influence processes that are observed to occur over time scales of hundreds of years and spatial scales of hundreds of kilometers, such as recurrence of great earthquakes. At the present time, our simulations of the Virtual California earthquake fault model involve a set of rectangular fault segments embedded in an elastic half space, inasmuch as our goal is to develop an understanding of such complex models. Thus we defer additional effects that are known to be important, including viscoelastic fault interactions, and rate and state friction laws, to future work. Our simulations indicate that elastic interactions combined with the nonlinearity in the frictional failure threshold law leads to self-organization of the statistical dynamics, producing 1) statistical distributions for magnitudes and frequencies of earthquakes that are bear characteristics similar to those possessed by the Gutenberg-Richter magnitude-frequency distribution as observed in nature; and 2) clear examples of stress transfer among fault activity described by stress shadows, in which an earthquake on one group of faults reduces the Coulomb failure stress on other faults, thereby delaying activity on those other faults. In this paper, we describe the current state of these modeling and simulation efforts for Virtual California 2001, a model for all the major active strike slip faults in California. Furthermore, we show how these simulations can be used to develop statistical earthquake forecasting techniques that are complementary to the methods used by the Working Group on California Earthquake Probabilities, but improve upon those methods in certain ways. Finally, we provide a brief discussion of future problems and issues related to the development of ensemble earthquake forecasting techniques.

Rundle, J. B., Rundle, P. B., Donnellan, A., Klein, W., Morein, G., Li, P., & Turcotte, D. L. (2005). Stress Transfer in Earthquakes and Forecasting: Inferences from Numerical Simulations. Journal of Geophysical Research, (in preparation).