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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, B05S02, doi:10.1029/2004JB003190, 2005

Significance of stress transfer in time-dependent earthquake probability calculations

Tom Parsons

U.S. Geological Survey, Menlo Park, California, USA


Abstract

A sudden change in stress is seen to modify earthquake rates, but should it also revise earthquake probability? Data used to derive input parameters permit an array of forecasts; so how large a static stress change is required to cause a statistically significant earthquake probability change? To answer that question, effects of parameter and philosophical choices are examined through all phases of sample calculations. Drawing at random from distributions of recurrence-aperiodicity pairs identifies many that recreate long paleoseismic and historic earthquake catalogs. Probability density functions built from the recurrence-aperiodicity pairs give the range of possible earthquake forecasts under a point process renewal model. Consequences of choices made in stress transfer calculations, such as different slip models, fault rake, dip, and friction are tracked. For interactions among large faults, calculated peak stress changes may be localized, with most of the receiving fault area changed less than the mean. Thus, to avoid overstating probability change on segments, stress change values should be drawn from a distribution reflecting the spatial pattern rather than using the segment mean. Disparity resulting from interaction probability methodology is also examined. For a fault with a well-understood earthquake history, a minimum stress change to stressing rate ratio of 10:1 to 20:1 is required to significantly skew probabilities with >80–85% confidence. That ratio must be closer to 50:1 to exceed 90–95% confidence levels. Thus revision to earthquake probability is achievable when a perturbing event is very close to the fault in question or the tectonic stressing rate is low.

Received 25 May 2004; accepted 8 September 2004; published 4 March 2005.

Keywords: stress transfer; earthquake probability; paleoseismology.

Index Terms: 7223 Seismology: Earthquake interaction, forecasting, and prediction (1217, 1242); 7221 Seismology: Paleoseismology (8036); 7250 Seismology: Transform faults; 8164 Tectonophysics: Stresses: crust and lithosphere.

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Citation: Parsons, T. (2005), Significance of stress transfer in time-dependent earthquake probability calculations, J. Geophys. Res., 110, B05S02, doi:10.1029/2004JB003190.