Thursday, March 17, 2011

California and Pacific North West Tsunami Risk

With all the talk about the possibility of underwater quakes just offshore of the USA's west coast causing tsunamis, I've wondered what the size of such waves might be. This article offers some estimates:

California tsunami could come with no warning
[...] Southern California could see a significant tsunami caused either by a large earthquake off Alaska or by undersea landslides spurred by smaller earthquakes off California. Northern California is at greater risk because of the Cascadia subduction zone, which runs along the Pacific Northwest coast.

Quakes off Alaska and the Pacific Northwest could create 15-foot waves in Southern California and 25-foot tsunamis in the northern part of the state, said California State Geologist John Parrish.

Tsunami inundation map of Long Beach. Click through for a larger version.And tsunamis caused by underwater landslides off Southern California could reach as high as 40 feet, although they would be localized and quick to dissipate, said Costas Synolakis, director of the Tsunami Research Center at USC.

That type of event is only expected to strike once in 2,000 or 3,000 years. But, as has happened in Japan, experts say all predictions may go out the window.

“Mother Nature is notorious for not obeying rules that we make,” Parrish said.


A quake off Alaska would give California six to nine hours lead time to clear the beaches before a tsunami struck, Parrish said. A temblor off the California-Oregon border, on the other hand, might give Northern California towns less than half an hour to prepare.

“That’s not very much time," he said, "especially if it’s 2 o’clock in the morning and you’re trying to wake up a whole town of people and get them up the hill.” [...]

I can only wonder how accurate the estimates are. No one will really know until it happens.

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