Northwest at risk of megaquake like one in Chile

Posted: Wednesday, March 03, 2010

LOS ANGELES - Just 50 miles off the Pacific Northwest coast is an earthquake hotspot that threatens to unleash on Seattle, Portland and Vancouver the kind of damage that has shattered Chile.

The fault has been dormant for more than 300 years, but when it awakens - tomorrow or decades from now - the consequences could be devastating.

Recent computer simulations of a hypothetical magnitude-9 quake found that shaking could last 2 to 5 minutes - strong enough to potentially cause poorly constructed buildings from British Columbia to Northern California to collapse and severely damage highways and bridges.

Such a quake would also send powerful tsunami waves rushing to shore in minutes. While big cities such as Portland and Seattle would be protected from severe flooding, low-lying seaside communities may not be as lucky.

The Pacific Northwest "has a long geological history of doing exactly what happened in Chile," said Brian Atwater, a geologist with the U.S. Geological Survey and University of Washington. "It's not a matter of if but when the next one will happen."

The last one hit in 1700, a magnitude-9 that sent 30- to 40-foot-tall tsunami waves crashing onto the coast and racing across the Pacific, damaging Japanese coastal villages.

There's an 80 percent chance the southern end of the fault off southern Oregon and Northern California would break in the next 50 years and produce a megaquake, according to Chris Goldfinger, who heads the Active Tectonics and Seafloor Mapping Laboratory at Oregon State University.



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