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Report: Chance of mega-quake hitting California increases

March 10, 2015

LOS ANGELES (AP) — Scientists are virtually certain that California will be rocked by a strong earthquake in the next 30 years. Now they say the risk of a mega-quake is more likely than previously thought.

The chance of a magnitude-8 quake striking the state in the next three decades jumped to 7 percent from 4.7 percent, mainly because scientists took into account the possibility that several faults can shake at once, releasing seismic energy that results in greater destruction.

While the risk of a mega-quake is higher than past estimates, it’s more likely — greater than 99 percent chance — that California will be rattled by a magnitude-6.7 jolt similar in size to the 1994 Northridge disaster. The chance of a Northridge-size quake was slightly higher in Northern California than Southern California — 95 percent versus 93 percent, according to a report released Tuesday by the U.S. Geological Survey.

“California is earthquake country, and residents should live every day like it could be the day of a big one,” USGS geophysicist and lead author Ned Field said.

The latest seismic calculations largely mirror previous findings issued by the USGS in 2008. Back then, scientists also determined that California faced an almost certain risk of experiencing a Northridge-size quake.

The new report included newly discovered fault zones and the possibility that a quake can jump from fault to fault. Because of this knowledge, the odds of a catastrophic quake — magnitude 8 or larger — in the next 30 years increased.

There is a 93 percent chance of a magnitude 7 or larger occurring over the same period and a 48 percent chance of a magnitude 7.5 — similar to previous estimates.

Thousands of quakes every year hit California, sandwiched between two of Earth’s major tectonic plates, the Pacific and North American plates. Most are too small to be felt.

Of the more than 300 faults that crisscross the state, the southern segment of the San Andreas Fault — which runs from central California to the Salton Sea near the U.S.-Mexico border — remains the greatest threat because it hasn’t ruptured in more than three centuries.

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