Statewide mega-quake on the San Andreas now thought possible

san-andreas-carrizo-plain.jpgOne of the lessons learned from the deadly Japanese earthquake of 2011 is that the San Andreas Fault may be capable of a much more potent quake than previously believed. A new study published in Nature offers evidence that the massive fault that defines the geography of California could snap along its entire length, unleashing a whomper of an earthquake that would hit north and south. Up to now, seismologists have assumed that a portion of the San Andreas in Central California where the Pacific and the North American plates creep past each other fairly smoothly would be immune from a violent snap — and that the so-called "creeping segment" would protect Southern California and Northern California from each other.

From Eryn Brown in the LA Times:

For decades, scientists have assumed the central portion of California's San Andreas fault acts as a barrier that prevents a big quake in the southern part of the state from spreading to the north, and vice versa. As a result, a mega-quake that could be felt from San Diego to San Francisco was widely considered impossible.

But that key fault segment might not serve as a barrier in all cases, researchers wrote Wednesday in the online edition of the journal Nature.

Using a combination of laboratory measurements and computer simulations, the two scientists showed how so-called creeping segments in a fault — long thought to be benign because they slip slowly and steadily along as tectonic plates shift — might behave like locked segments, which build up stress over time and then rupture.

Such a snap caused the 9.0-magnitude Tohoku-Oki earthquake that hit Japan in 2011, triggering a tsunami, killing nearly 16,000 people and destroying the Fukushima Daiichi nuclear power plant. Forecasters had not believed such a large quake was possible there.

A supposedly stable section of fault also ruptured during the 1999 Chi-Chi quake in Taiwan, a 7.6-magnitude temblor that killed more than 2,400 people.

Enjoy your day. Here's another explainer on how the creeping segment mechanism is thought to work on long faults such as the San Andreas.

Interactive map of the San Andreas Fault

Photo: Elkhorn Scarp on the Carrizo Plain/SanAndreasFault.org

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