Several retrospective analyses have proposed that significant increases in moment release occurred prior to many large earthquakes of recent times. However, the finding of Accelerating Moment Release (AMR) strongly depends on the choice of several parameters (magnitude range, area being considered surrounding the events, time period prior to the large earthquake) and the AMR analysis may appear as a data-fitting exercise with no new predictive power. As AMR may relate to a state of high stress around the eventual next epicenter, it is interesting to compare the AMR results to models of stress accumulation in California. Instead of assuming a complete stress drop on all surrounding fault segments implied by the back-slip stress lobe method (Bowman and King, 2001), we consider that stress evolves dynamically, punctuated by the occurrence of earthquakes and governed by the elastic and viscous properties of the lithosphere (Freed et al., 2007). We generate several sensitivity tests of the method, as well as a first grid-search analysis for a few large events in Southern California. We also present here a comparison of a more general AMR analysis from 1965 to today with maps of Coulomb stress changes due to all M7.0 since 1812, subsequent postseismic relaxation and interseismic strain accumulation.
Berkeley Seismological Laboratory
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