Stress evolution of the San Andreas fault system: Recurrence interval versus locking depth

Abstract

Major ruptures along the San Andreas Fault System (SAFS) are driven by stress that has accumulated in the upper locked portion of the crust. The present-day stress accumulation rate on any given fault segment is fairly well resolved by current geodetic measurements. Model stress accumulation rates vary between 0.5 and 7 MPa per century and are inversely proportional to earthquake recurrence intervals. In contrast, the total accumulated stress on a given fault segment is poorly resolved since it depends on the uncertain rupture history of each fault over the past few thousand years. We simulate accumulated stress at crustal depths for both past and present-day conditions by assuming complete release of accumulated slip deficit during major ruptures. These speculative results indicate that the southern San Andreas, which has not ruptured in a major earthquake in over 300 years, is currently approaching a threshold stress level. Copyright 2009 by the American Geophysical Union.