LOS ANGELES (AP) — If a monster earthquake struck off Alaska’s coast, tsunami waves would rush toward California, swamping the nation’s largest port complex and causing major economic damage.

That’s according to a hypothetical scenario released Wednesday by the U.S. Geological Survey and others to help emergency planners prepare.

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Tsunamis are a rare but real threat in California. After the 2011 Japan disaster, tsunami waves surged across Pacific and damaged the Northern California commercial fishing village of Crescent City.

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Scientists say a closer offshore quake would create more havoc, flooding the ports of Los Angeles and Long Beach, forcing coastal communities to evacuate and destroying boats and small craft.

The tsunami scenario is similar to a quake exercise released several years ago designed to prepare for a big one on the San Andreas Fault.

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