On August 26 , 2012 near Brawley , a swarm of more than 300 small to moderate earthquakes occurred with the largest two reaching a maximum of 5.3 and 5.5 . Some light cosmetic damage was found on some older buildings in downtown Brawley . Earthquake swarms are not unusual for the area . In 2005 , also near Brawley , there was a swarm with a peak magnitude of 5.1 , while in 1981 a swarm included one quake which was measured at 5.8 . The swarm activity is not understood completely , but the new restlessness could generate data that will help scientists to gain a better understanding of the region . According to a geologist at the United States Geological Survey ( USGS ) , such swarms are typical for the Brawley zone : " The area sees lots of events at once , with many close to the largest magnitude , rather than one main shock with several much smaller aftershocks . " The Imperial Valley of southern California experiences high rates of seismicity with a pronounced portion of the activity occurring within the Brawley Seismic Zone that separates the San Andreas fault to the north and the Imperial fault to the south . The Imperial fault was the source of the 1940 El Centro earthquake and the 1979 Imperial Valley earthquake . There was more than of surface rupture associated with the 1979 event along the northwest trending Imperial fault from just north of the Mexico – United States border to an area south of Brawley and the BSZ was found to have ruptured , with surface cracks , for a length of . The 1940 and 1979 mainshocks were of similar size and both were followed by damaging aftershocks near Brawley
1979 Imperial Valley earthquake
1979 Imperial Valley earthquake
Brawley Seismic Zone