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Scientists predict North American tsunami inevitable

Tsunamis much like the deadly wall of water that swept across the Indian Ocean a year ago have struck the US West Coast at least 16 times, most recently in 1700.

It is only a matter of time before another one strikes. And when it does, some coastal cities may have as little as 15 minutes warning before the tsunami reaches them, said Chris Goldfinger, an Oregon State University (OSU) professor of marine geology.

"And it just keeps coming," he said of the tsunami wave. "It may take another 15 minutes just to get to the peak."

Tsunamis are very long waves that are led by a depression in the water. When the leading edge of the tsunami gets close to shore, the depression arrives first, often draining the beaches of water before the wave arrives.

"People run out on the sand and you see fish flopping," Goldfinger said. "It's rare to see a big wave coming in. You don't see a breaking wave, you don't see a curl. It just hits you like a wall."

Goldfinger, along with other researchers, is working at the Hinsdale Wave Research Laboratory at OSU to study tsunami behavior and find ways to reduce the risk to coastal cities, or at least increase the chances of survival.

The Hinsdale facility includes a US$4.8 million tsunami wave basin, an enormous tank with a wave generator that can simulate tsunami waves as they approach a coastline and assess the level of damage they can cause.

The lab -- the largest of its kind in the world -- has run a sophisticated simulation on the impact a tsunami could have on the densely populated Puget Sound area of Washington state, which includes the Seattle area. Researchers plan to release the results at an international meeting in February, Cox said.

The coast is at risk because of a long, sloping fault called the Cascadia Subduction Zone stretching 965km undersea from mid-Vancouver Island in Canada to Northern California.

The zone is the junction of two huge sections of the Earth's crust -- called the Juan de Fuca and North America plates -- where new ocean floor is being created and pushed beneath the continent, building up pressure that sets the stage for enormous earthquakes that reach magnitude 9 or higher.

Those quakes have occurred with regular frequency over the past 10,000 years, flooding what has become one of the most heavily populated areas of the US and Canada.

Researchers have found evidence of 23 major quakes over those millennia, and at least 16 spawned tsunamis that inundated most of the coast.

Sediment samples drilled from the ocean floor in 1999 and 2002 show a clear pattern that has been confirmed with radiocarbon dating, geological evidence and statistical analysis, said Goldfinger.

Nationally, more than 200 tsunamis have been recorded since the 1700s, killing more people than all other earthquake-related incidents combined, according to OSU researchers.
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