Fault coupling and potential for earthquakes on the creeping section of the central San Andreas Fault

Abstract

The 150km long central section of the San Andreas Fault (CSAF) in central California creeps at the surface and has not produced a large earthquake historically. However, sections of the San Andreas Fault to the north and south are known to have ruptured repeatedly in M~7-8 earthquakes. It is currently unclear whether the creeping CSAF could rupture in large earthquakes, either individually or along with earthquakes on the locked sections to the north and south. We invert Global Positioning System and interferometric synthetic aperture radar data with elastic block models to estimate the degree of locking on the CSAF and place bounds on the moment accumulation rate on the fault. We find that the inferred moment accumulation rate is highly dependent on the long-term fault slip rate, which is poorly constrained along the CSAF. The inferred moment accumulation rate, normalized by shear modulus, ranges from 3.28×104 to 5.85×107m3/yr, which is equivalent to a Mw=5.5-7.2 earthquake every 150years for a long-term slip rate of 26mm/yr and Mw=7.3-7.65 for a long-term slip rate of 34mm/yr. The comparisons of slip distributions with microseismicity and repeating earthquakes indicate a possible locked patch between 10 and 20km depth on the CSAF that could potentially rupture with Mw=6.5. ©2014. American Geophysical Union. All Rights Reserved.