Subduction zone quake could also hit Northwest

Northwesterners should pay close attention to the tragedy unfolding in Japan, because the same thing is headed our way, scientists say.

The massive earthquake that struck Thursday night, followed within minutes by tsunami waves 20 feet high or more, is almost identical to what the coast of the Pacific Northwest will see when the offshore fault called the Cascadia subduction zone ruptures.

"It's the best example of what we're going to have, and I'm sure Japan is more prepared than we are," said John Vidale, head of the Pacific Northwest Seismic Network at the University of Washington. The Cascadia fault last ruptured in 1700, generating a magnitude 9 earthquake and a tsunami that may have been bigger than the one that battered Japan. Major earthquakes on the Cascadia fault occur every 400 to 500 years, though some new evidence suggest they could be much more frequent.

The magnitude 8.9 Japan quake was preceded by a series of magnitude 7 foreshocks that scientists will be studying closely, Vidale said. "We're very curious to see if something was going on that might have provided warning had they known how to interpret it properly."

Some scientists say Thursday's quake may have been as large as magnitude 9.1. If that proves correct, the official number could be revised upward.

Scientists at the National Oceanic and Atmospheric Administration in Seattle raced to their offices Thursday night, shortly after the quake hit, to help forecast where tsunami waves were headed.

A network of tsunami warning buoys launched after the 2004 Indian Ocean tsunami paid off in a big way, said Eddie Bernard, leader of NOAA's Pacific Marine Environmental Laboratory.

Two buoys off the coast of Japan picked up the tsunami wave minutes after the quake. That information allowed modelers in Seattle to predict the wave's path and its likely impact on Hawaii and the U.S. West Coast.

The location of the quake and its orientation means most of the West Coast was spared major impact, Bernard said.

"It's good luck and good location," he said. "If the earthquake had been somewhere else, the effects on the Washington coast could have been much worse."

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Information from: The Seattle Times, http://www.seattletimes.com