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San Andreas fault has produced far more earthquakes than previously believed, study finds

August 20, 2010 |  9:27 am

Major earthquakes along the San Andreas fault have occurred far more often than previously believed, according to a landmark study released Friday that suggests California is overdue for a huge temblor.

The long-awaited study came after scientists spent years studying the geology of the Carrizo Plain area of the San Andreas, which is about 100 miles northwest of Los Angeles.

The last massive earthquake on that part of the fault occurred in 1857. But researchers from UC Irvine and Arizona State University found that earthquakes have occurred as often as every 45 to 144 years.

That would make the region overdue for the type of catastrophic quake often referred to as "The Big One."

The finding adds weight to the view of many Southern California seismologists that the San Andreas has been in a quiet period and that a major rupture is possible.

The research, published Friday in the journal Geology, used charcoal samples to look for earthquake activity going back centuries.

"What we know is for the last 700 years, earthquakes on the southern San Andreas fault have been much more frequent than everyone thought," UCI researcher Sinan Akciz said in a statement. "Data presented here contradict previously published reports."

-- Rong-Gong Lin II

Updated, 6:21 p.m.: Study shakes up scientists' view of San Andreas fault earthquake risk