Rheological controls on fault loading rates in northern California following the 1906 San Francisco earthquake

Abstract

To estimate seismic hazard in complex, multiple fault systems, it is necessary to understand how stresses within the system are transferred. Accurate estimates of loading rate due to far-field tectonic motion and postseismic transients following large earthquakes are required. Using plausible lower crustal rheologies constrained by observations following the 1906 San Francisco earthquake, I show that postseismic relaxation may play a significant role in reloading the coseismic fault, providing 60-80% of the stress released during great earthquakes. Further, postseismic stressing rates along neighboring faults are highly dependent on the geometry and rheology of the lower crust/upper mantle. This implies that tectonic loading rate estimates are also highly dependent on lower crustal/upper mantle structure. Thus, improvement of seismic hazard estimates within complex, multiple fault systems is dependent on a better understanding of structure and rheology at depth. Copyright 2004 by the American Geophysical Union.