December 30, 2004
Scientists: Tsunami Could Hit West Coast
Tsunami scientists and public safety officials are closely watching an earthquake-prone nation with thousands of miles of crowded coastlines for signs of an imminent disaster. Indonesia? Japan? Try the United States.
Experts say the West Coast could experience a calamity similar to the one they have been watching unfold half a world away.
"People need to know it could happen," said geologist Brian Atwater of the U.S. Geological Survey.
Scientists say grinding geologic circumstances similar to those in Sumatra also exist just off the Pacific Northwest coast. They are a loaded gun that could trigger a tsunami that could hit Northern California, Washington, Oregon and British Columbia in minutes - too fast for the nation's deep-sea tsunami warning system to help.
In fact, Atwater said there was a 9.0 earthquake under the Pacific more than 300 years ago that had devastating consequences. He and other scientists last year reported finding evidence of severe flooding in the Puget Sound area in 1700, including trees that stopped growing after "taking a bath in rising tide waters."
The danger rests just 50 miles off the West Coast in a 680-mile undersea fault known as the Cascadia subduction zone that behaves much like one that ruptured off Sumatra. The 1700 quake occurred along the Cascadia fault.
Scientists say a giant rupture along the fault would cause the sea floor to bounce 20 feet or more, setting off powerful ocean waves relatively close to shore. The first waves could hit coastal communities in 30 minutes or less, according to computer models.
Seattle; Vancouver, British Columbia; and other big cities in the region probably would be relatively protected from deadly flooding because of their inland locations. But other, smaller communities could be devastated.
And while buildings in the United States are far more solid than the shacks and huts that were obliterated in some of Asia's poor villages, few structures could withstand nearby tremors as powerful as those that occurred Sunday in Sumatra.
Moreover, such a quake would be way too close to shore for the nation's network of deep-sea wave gauges to be of any help.
Even in the case of quakes happening farther out in the Pacific or in Alaska, the U.S. warning system might not be adequate.
The network - which consists of six deep-sea instruments in Alaska, Washington, Oregon and Hawaii and near the equator off the coast of Peru - is thin and scattered, and at least two of the gauges in Alaska are not even reporting daily wave readings. Also, predicting where a tsunami is likely to come ashore cannot be done with the kind of precision seen in hurricane forecasts.
Eddie N. Bernard, who directs the network for the National Oceanic and Atmospheric Administration, said the six sensors are the "bare minimum" for adequate warning. He said there are plans to expand the system to 20 sensors in the next five years, including 10 gauges for the seismically active Aleutian Islands.
Whether the continental United States is vulnerable to tsunamis from Asian earthquakes is another question. Hawaii and parts of Alaska certainly are exposed, but whether earthquake fault lines in Japan and Southeast Asia are oriented in the right directions to send tsunamis all they way to the Lower 48 states is debatable.
As for the Atlantic Coast, a tsunami is considered extremely unlikely.
Some computer models suggest East Coast cities are vulnerable to a large tsunami if there were a huge volcanic eruption and landslide in the Canary Islands, off northwest Africa. But other researchers say such an event would happen only once in 10,000 years, and such a disruption is unlikely to occur all at once.
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