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The 7th July 2010, M5.4 Borrego Earthquake Located near the Coyote Creek Segment of the San Jacinto Fault
Egill Hauksson, Nancy King, Lucy Jones, Sinan Akciz, Bob Dollar, Ken Hudnut, Kate Hutton

A M5.4 earthquake occurred in southern California at 4:53 pm (Pacific Time) about 30 miles south of Palm Springs, 25 miles southwest of Indio, and 13 miles north-northwest of Borrego Springs.  The earthquake occurred near the Coyote Creek segment of the San Jacinto fault, which is one of the strands of the San Jacinto fault. The earthquake exhibited sideways horizontal motion to the northwest, consistent with slip on the San Jacinto fault.  It was followed by more than 60 aftershocks of M>1.3 during the first hour.  Seismologists expect continued aftershock activity.

In the last 50 years, there have been four other earthquakes in the magnitude 5 range within 20 km of this location: M5.8 1968, M5.3 on 2/25/1980, M5.0 on 10/31/2001, and M5.2 on 6/12/2005. The biggest earthquake near this location was a M6.0 Buck Ridge earthquake on 3/25/1937.

The earthquake was felt all over southern California, with strong shaking near the epicenter.

The San Jacinto fault, along with the Elsinore, San Andreas, and other faults, is part of the plate boundary that accommodates about 2 inches/year of motion as the Pacific plate moves northwest relative to the North American plate. The largest recent earthquake on the San Jacinto fault, near this location, the M 6.5 1968 Borrego Mountain earthquake April 8, 1968, occurred about 25 miles southeast of the July 7 M 5.4 earthquake.

This M5.4 earthquake follows the 4th of April 2010, Easter Sunday, Mw7.2 earthquake, located about 125 miles to the south, well south of the US Mexico international border.  A M4.9 earthquake occurred in the same area on June 12th at 8:08 pm (Pacific Time).  Thus this section of the San Jacinto fault remains active. 

Seismologists are watching two major earthquake faults in southern California.  The San Jacinto fault, the most active earthquake fault in southern California, extends for more than 100 miles from the international border into San Bernardino and Riverside, a major metropolitan area often called the Inland Empire.  The Elsinore fault is more than 110 miles long, and extends into the Orange County and Los Angeles area as the Whittier fault.  The Elsinore fault is capable of a major earthquake that would significantly affect the large metropolitan areas of southern California.  The Elsinore fault has not hosted a major earthquake in more than 100 years.  The occurrence of these earthquakes along the San Jacinto fault and continued aftershocks demonstrates that the earthquake activity in the region remains at an elevated level.  The San Jacinto fault is known as the most active earthquake fault in southern California.  Caltech and USGS seismologist continue to monitor the on going earthquake activity using the Caltech/USGS Southern California Seismic Network and a GPS network of more than 100 stations. 

For additional information check, www.scsn.org, and http://earthquake.usgs.gov/

From USGS-Caltech Talking Points, Version 1.0 July 7, 2010 (18:50 PDT)