When “The Big One” Hits, it Might Not Be Alone, Earthquake Study Says

What if there's not just one "Big One," but several?

Twelve faults able to produce high-magnitude earthquakes, above 7 on the Richter scale, criss-cross Southern California, and a new study has scientists wondering if a big shock along one of the faults could cause others to violently shake as well.

"These are going to be Southern California-wide effects," said James Dolan, USC professor of Earth Sciences and the author of the study.

It's been over a century since the last true "Big One" hit California -- that would be San Francisco's 7.8-magnitude shaker in 1906 -- but Dolan is investigating whether really big earthquakes can put pressure on other faults, causing big earthquakes there as well.

His team studied how much SoCal's second largest fault moved each year during periods when there were many earthquakes and when it was quiet. They theorize that the strength of the fault was related to that of other faults in the system, said their study abstract posted online.

"We have flurries of big earthquakes separated by long periods of relative seismic quiet," Dolan said.

They presented their findings on cycles of activity at a recent meeting of the Seismological Society of America.

U.S. Geological Survey scientists said in March they are virtually certain that a strong earthquake like the one that hit Northridge in 1994 will strike California in the next 30 years, and they placed the likelihood of it being a magnitude-8 temblor at 7 percent. They mentioned the possibility that several faults can shake at once as well.

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