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Published February 16, 2017 | public
Journal Article

Evolution of seismicity near the southernmost terminus of the San Andreas Fault: Implications of recent earthquake clusters for earthquake risk in southern California


Three earthquake clusters that occurred in the direct vicinity of the southern terminus of the San Andreas Fault (SAF) in 2001, 2009, and 2016 raised significant concern regarding possible triggering of a major earthquake on the southern SAF, which has not ruptured in more than 320 years. These clusters of small and moderate earthquakes with M ≤ 4.8 added to an increase in seismicity rate in the northern Brawley seismic zone that began after the 1979 M_w 6.5 Imperial Valley earthquake, in contrast to the quiet from 1932 to 1979. The clusters so far triggered neither small nor large events on the SAF. The mostly negative Coulomb stress changes they imparted on the SAF may have reduced the likelihood that the events would initiate rupture on the SAF, although large magnitude earthquake triggering is poorly understood. The relatively rapid spatial and temporal migration rates within the clusters imply aseismic creep as a possible driver rather than fluid migration.

Additional Information

© 2017 American Geophysical Union. Received 27 NOV 2016; Accepted 20 JAN 2017; Accepted article online 24 JAN 2017; Published online 9 FEB 2017. Supported by USGS/NEHRP: G16AP00147, National Science Foundation (NSF): EAR-1550704, and Southern California Earthquake Center (contribution 7176) and funded by NSF EAR-1033462 and USGS G12AC20038. Figures done with PMG from Wessel et al. [2013]. Used data are from the Caltech/USGS SCSN; doi:10.7914/SN/CI; stored at Southern California Earthquake Data Center (SCEDC) doi:10.7909/C3WD3xH1.

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