M5.7 - SOUTHERN CALIFORNIA

Tectonic Summary

The 14th June 2010, M5.7 Aftershock of the 4th April M7.2 El Mayor-Cucapah Earthquake Along the US Mexico border

A M5.7 aftershock to the M7.2 April, 4th 2010 Easter Sunday mainshock, called El Mayor-Cucapah earthquake, occurred at 9:27 pm (Western Standard Time) on June 14th, about 5 miles southeast of the Imperial County community of Ocotillo, at the US Mexico border. This aftershock was the largest so far of the M7.2 El Mayor-Cucapah sequence. This aftershock was located within the large cluster of aftershocks at the northwest end of the ongoing aftershock sequence. The M5.7 event was followed by its own vigorous aftershock sequence, with four M4+ and 35 M3 to M4 events, during the first 12 hours.

The M5.7 June 14th event probably occurred on a northwest striking fault that follows the trend of the Elsinore fault in this region. 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 this aftershock and its own aftershock sequence, and the M4.9 earthquake that occurred along the San Jacinto fault on June 12th 2010 demonstrate 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.