Study suggests San Andreas more overdue than previously thought

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Susan Valot/KPCC

The San Andreas Fault looks like a scar (on the bottom) in the Carrizo Plain area. This image was taken from the air in 2007.

A new study suggests the San Andreas Fault may be more overdue for a big earthquake than scientists previously thought. Researchers from UC Irvine and Arizona State University took a closer look at the fault that runs almost the length of California.

They looked at the section of the fault on the Carrizo Plain, about 100 miles north of Los Angeles. That’s where you can actually see the fault rupture on the surface, like a scar.

The scientists found evidence that the fault has set off large earthquakes as often as every century-and-a-half — and sometimes as often as every half-century.

That’s a much smaller interval than the widely accepted view that the San Andreas triggers big quakes every 250 to 400 years.

The last major quake on the fault was more than 150 years ago — the 7.8-magnitude Fort Tejon Earthquake back in 1857.

That doesn’t necessarily mean the “Big One” hits tomorrow, but the scientists say we need to be ready with earthquake supplies. UCI seismologist Lisa Grant Ludwig says you can make an analogy to your everyday life.

"There are storm clouds gathered on the horizon," she says. "Does that mean it's definitely going to rain? No, but when you have that many clouds, you think, 'I'm going to take my umbrella with me today.' That's what this research does: It gives us a chance to prepare."

The researchers say while earthquakes on the San Andreas may be more frequent, they also may be smaller. The scientists agree that figuring out when earthquakes will hit on the San Andreas Fault is complex.

The study will be published in the September 1 issue of Geology.

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