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Earthquake warning for California fault line proves accurate

July 8, 2010 |  9:01 am

 http://www.uoregon.edu/~rdorsey/SJFig1.gif

California earthquake experts have been saying for weeks that the 7.2 temblor on Easter Sunday in Mexicali had placed pressure on two Southern California fault lines -- the Elisnore and the San Jacinto -- making quakes there more likely.

They proved prescient. 

The 5.4 earthquake that rattled Southern California on Wednesday evening appeared to hit along the San Jacinto fault, officials said. That fault runs roughly from the Salton Sea area northwest through the San Jacinto Mountains toward San Bernardino.

Scientists are now studying how the Mexicali quake changed the pressure of various Southern California fault lines. One questions: Did the temblor make quakes more likely along more dangerous fault lines, such as the Whittier — which produced the deadly 1987 Whittier Narrows quake? Scientists are particularly interested in the Whittier fault because it's connected to the Elsinore and runs under heavily populated areas.

The 5.4 quake on Wednesday wasn't exactly an aftershock of Mexicali.

"We've been calling those 'triggered earthquakes,' " Caltech seismologist Kate Hutton said, referring to temblors north of the aftershock zone that runs from the Gulf of California to Ocotillo, Calif., near the Mexican border.

"We've been able to see an increase in activity," Hutton said. Wednesday's earthquake was the largest to hit the Elsinore and San Jacinto fault zones since the April 4 shaker.

-- Rong-Gong Lin II and Hector Becerra

Map credit: University of Oregon

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