Monday, August 27, 2012

Quake Swarm Strikes California

More than 210 earthquakes hit state of California on Sunday with the strongest measured 5.5. The earthquakes were felt as far away as San Diego, Temecula and San Clemente. The first quake occurred about three miles northwest of Brawley, registered as magnitude 3.8 temblor. It was followed by a swarm of quakes in the same area, according to the U.S. Geological Survey.

The earthquakes are occurring on a northeast striking fault zone located about 6 km north of the northwest end of the mapped Imperial Valley fault. This is within the area called the Brawley Seismic Zone. The BSZ extends from the northern end of the Imperial fault to the southern end of the San Andreas fault. It has been characterized by swarms that have occurred in the 1930s, the 1960s, and 1970s. The last significant swarm before this one occurred in 2005 along the south shore of the Salton Sea, with the largest event of M5.1. In 1981 there was swarm-like activity called the Westmoreland sequence, with a largest event of M 5.8, which occurred 8 km to the northwest of to days activity. Some of the aftershocks of the Mw6.4 1979 earthquake occurred in the same general area.

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