Lower Crustal Controls on Postseismic Reloading Rates in the San Francisco Bay Area Following the 1906 San Francisco Earthquake

S. J. Kenner , University of Kentucky
P. Segall, Stanford University

Abstract

        To effectively estimate future seismic hazard within complex, multiple fault systems such as the San Andreas fault system, it is necessary to understand how stresses are transferred within that system.  Accurate estimates of stress loading rates on faults due to far-field tectonic motion and postseismic transients following large earthquakes are required.  We investigate postseismic loading rates along major northern California faults following the 1906 San Francisco earthquake.  Using the best-fitting numerical models of Kenner and Segall [2002], we show that relaxation of time-dependent material in the lower crust and upper mantle may play a significant role in reloading the coseismic fault, providing 60-80% of the stress released during a great earthquake.  We also demonstrate that postseismic stressing rates along neighboring faults are highly dependent on the geometric structure and rheology of the lower crust and upper mantle.  It can be inferred from these results that tectonic loading rate estimates are also highly dependent on modeled lower crustal/upper mantle structure.  In consequence, future improvement of seismic hazard estimates within complex, multiple fault systems depend critically on obtaining a better understanding of structure and rheology at depth.

Reference: Kenner, S.J., and P. Segall, Lower Crustal Controls of Postseismic Reloading Rates in the San Francisco Bay Area Following the 1906 San Francisco Earthquake, in prep, Geophysical Research Letters, August 2002.