Big quakes on San Andreas fault more frequent than thought

Earthquakes have rocked the powerful San Andreas fault far more often than previously thought, according to a new study by UC Irvine and Arizona State University researchers.

They have found that large ruptures have occurred on the fault as often as every 45 to 144 years. But the last big quake was in 1857, more than 150 years ago.

“If you’re waiting for somebody to tell you when we’re close to the next San Andreas earthquake, just look at the data,” said UCI seismologist Lisa Grant Ludwig.

Ludwig hopes the findings will serve as a wake-up call to Californians who’ve grown complacent about the risk of major earthquakes.

That translates into having ample water and other supplies on hand, safeguarding possessions in advance, and establishing family emergency plans.

For regulators, Ludwig advocates new policies requiring earthquake risk signs on unsafe buildings and forcing inspectors in home-sale transactions to disclose degrees of risk.

The study revealed that the widely believed theory that a major earthquake happened on the fault every 250 to 400 years was inaccurate.

“What we know is for the last 700 years, earthquakes on the southern San Andreas fault have been much more frequent than everyone thought,” said Sinan Akciz.

The findings are to be published in the Sept. 1 issue of Geology.

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