A Caltech Library Service

A seismotectonic analysis of the Anza Seismic Gap, San Jacinto Fault Zone, Southern California

Sanders, Chris O. and Kanamori, Hiroo (1984) A seismotectonic analysis of the Anza Seismic Gap, San Jacinto Fault Zone, Southern California. Journal of Geophysical Research B, 89 (B7). pp. 5873-5890. ISSN 0148-0227. doi:10.1029/JB089iB07p05873.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


Small earthquake epicenters near the Anza seismic gap define a 20-km quiescent segment of fault bounded to the northwest and southeast by areas of relatively high seismicity. Recent moderate earthquakes on and near the San Jacinto fault in the gap and their relatively depressed aftershock activity indicate that the fault is seismogenic and highly stressed but locked by some mechanism. The locked nature of the fault may be due to relatively high compressive stress normal to the fault resulting from the convergent geometries of the local, active, discontinuous faults and the oblique orientation of the regional maximum compressive stress. Strain is not being relieved by aseismic fault creep. A swarm of small earthquakes in the crustal block 13 km southwest of the Anza gap beneath the Cahuilla Valley recently released stress in an area which was previously highly active before the 1918 (M 6.8) and 1937 (M_L 6.0) earthquakes. The occurrence of these periods of increased seismicity near Cahuilla in the years immediately before the nearby (closer than 35 km) large earthquakes and the recent swarm suggest that the ground beneath Cahuilla may be acting as a stress meter signaling the presence of high stresses before large local earthquakes. The length of the quiescent fault segment suggests potential for about an M 6.5 earthquake if the entire segment ruptures at once.

Item Type:Article
Related URLs:
URLURL TypeDescription
Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1984 American Geophysical Union. Received May 10, 1983; revised December 9, 1983; accepted January 25, 1984. We appreciate numerous informative discussions with many individuals, including Doug Given and Bill Stuart of the U.S. Geological Survey, Pasadena; Karen McNally, Jim Pechman, and Ed Corbett of the Caltech Seismological Lab; Kerry Sieh and Robert Hill of the Caltech Geology Department; Greg Lyzenga of the Jet Propulsion Laboratory; and Robert Sharp and Tom Hanks of the U.S. Geological Survey, Menlo Park. We also thank Marianne Walck, Kerry Sieh, Robert Sharp, and an anonymous reviewer for their thoughtful editing. The research was supported by USGS contracts 1-14-08-197 56 and 64628, 14-08-0001-19266 and 20546. This is contribution 3859, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125.
Funding AgencyGrant Number
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences3859
Issue or Number:B7
Record Number:CaltechAUTHORS:20141105-131942852
Persistent URL:
Official Citation:Sanders, C. O., and H. Kanamori (1984), A seismotectonic analysis of the Anza Seismic Gap, San Jacinto Fault Zone, southern California, J. Geophys. Res., 89(B7), 5873–5890, doi:10.1029/JB089iB07p05873.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51312
Deposited By: Jason Perez
Deposited On:06 Nov 2014 20:46
Last Modified:10 Nov 2021 19:09

Repository Staff Only: item control page