General Information


Region :
Coso area, southern Owens Valley
Date : 11/27/96
Time (gmt) : 20:17:23
Magnitude : Mw 5.1
Latitude : 36.075
Longitude : -117.650
Depth (km) 2

3-axis raw seismogram recorded at HMC



Coso Earthquake of November 27, 1996

There was a moderate earthquake in the Coso area of southern California on November 27, 1996 at 20:17:23 GMT (12:17:23 PST). The hypocenter was located at 36.075N 117.650W with a depth of 1 to 3 km. The epicenter is 17 miles ENE of the town of Little Lake. The preliminary local magnitude (ML) was 5.0. The preliminary moment magnitude (Mw) from UC Berkeley was 5.1 . Focal mechanisms from both the first motions and the long-period surface waves showed a strike-slip solution with NE and NW nodal planes. The distribution of aftershocks tends to be elongated in a northeast-southwest direction suggesting left-lateral slip on a northeast trending fault plane, but the fault plane is still unclear.

In the 18 hours since the mainshock, we have recorded over 225 aftershocks with 6 M3 events. Currently, the rate of recorded aftershocks has declined to 5-10 small earthquakes per hour. In hindsight, we identified a small "foreshock" sequence that occurred 27 hours before the mainshock and had 3 M2 earthquakes with several smaller events.

The closest telemetered strong-motion instrument recorded 2% g at Ridgecrest, about 40 km to the south. The region surrounding the earthquake is sparsely populated and there have been no reports of damage.

This earthquake occurred in the area of the Coso geothermal fields which has frequent small earthquakes. This region has had vigorous swarms of many small earthquakes with several M4's in 1981, 1982-83, 1985 and 1992. The 1995-96 Ridgecrest sequence that included 3 M5 events occurred in an area 25 to 30 km to the south.

List of current seismicity in southern California can be obtained by "finger quake@scec.gps.caltech.edu" Maps of ground motion and seismicity for the current sequence can be seen on the USGS homepage at http://www-socal.wr.usgs.gov

contributed by:

Jim Mori

Southern California Seismic Network

USGS/Caltech


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