SCEC Award Number 02050 View PDF
Proposal Category Science Proposal
Proposal Title Incorporating Stress Triggering Concepts into Earthqauke Probability Estimates 
Investigator(s)
Name Organization
Jeanne Hardebeck University of California, San Diego
Other Participants
SCEC Priorities SCEC Groups N/A, N/A, Seismology
Report Due Date N/A Date Report Submitted N/A
Project Abstract
 Stress triggering and fault interaction concepts are beginning to be incorporated into quantitative earthquake probability estimates. However, existing methods are limited in their range of compatible earthquake nucleation models. I introduce a new general method for translating stress changes into earthquake probability changes, which can potentially be used with any physical fault model. I demonstrate that this model works better for the assumption of rate-and-state friction than a prior model that “double-counts” the stress change by applying a Coulomb stress threshold and a rate-and-state model in combination. Given the large uncertainties in earthquake probability calculations, it is unclear whether the small probability changes resulting from stress transfer are significant and meaningful for the purposes of seismic hazard assessment. I present an exploration of parameter space that demonstrates that the probability changes due to stress triggering are significant only for time intervals that are short compared to the repeat time of the target fault. Therefore stress change calculations will be useful in long-term seismic hazard assessment only for low slip-rate faults. Otherwise, stress triggering calculations are best utilized in the short-term immediately following a major earthquake.
Intellectual Merit One of the fundamental goals of SCEC is to move towards physical models of earthquake occurrence, and incorporating these physical models into seismic hazard assessment. This work contributes towards our ability to implement physical models of earthquake triggering in a probabilistic framework.
Broader Impacts This project contributed to the training of a female early-career scientist (the PI was a post-doc at the time of this project.)
Exemplary Figure Figure 3. Contours indicate percent probability change as a function of the stress change (normalized by the seismic cycle stress) and the length of the time interval (normalized by the event repeat time on the target fault) which is assumed to start at the time of the stress change. Because of the normalization, these Figures are appropriate for faults with any stressing rate. Each panel shows results for a stress change occurring at a different time during the seismic cycle. The shaded region indicates roughly where the conditional probability change will not be statistically significant at the 1σ level. I assume that the original probability distribution is log-normal with a coefficient of variation b = 0.5, and that Aσ is 0.1 of the seismic cycle stress (following Dieterich [1994]). The symbols show results using data from a study of Landers earthquake (square), Toda et al. [1998] (triangles), Parsons et al. [2000] (circles), and Toda and Stein [2002] (diamond).

Hardebeck, J. L., Stress Triggering and Earthquake Probability Estimates, J. Geophys. Res., 109, B04310, doi:10.1029/2003JB002437, 2004. [SCEC contribution number 764.]