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Possible next Tsunami victim: America’s West Coast

North America’s West Coast could be the next victim of tsunamis as severe as those that devastated southeast Asia on Sunday, geologists say.

Similar giant waves, spurred by undersea earthquakes, have repeatedly struck this coast in the past, according to a University of Oregon geoscientist. Native legends confirm this, he added.

“From northern California to Vancouver, B.C., the Native American stories tell of battles between gods along the coast, whales carried over the land and dropped, rivers becoming salty during the flood, and canoes thrown into trees,” said Ray Weldon, who researches and teaches about of geologic hazards at the university.

Geologists believe a tsunami caused by a magnitude 9.0 earthquake occurred on Jan. 26, 1700. It wiped out local tribal villages and causing damage as far away as Japan, which has written records of the event.

Weldon said he hopes coastal residents will be learn about the tsunami potential in light of the devastation along the coasts of nine Asian nations on the Indian Ocean.

Weldon is leading a team of scientists studying uplift – the gradual rise of the Earth’s surface – along the coast. This helps predict the size of future earthquakes and tsunamis. A comparison of modern uplift rates in the Pacific Northwest reveals many similarities to the rates predicted by models of past earthquakes, like the one of 1700, Weldon added.

The uplift reveals that a subduction zone – an area on a planet's crust in which the edge of an oceanic continental plate is being pushed beneath another plate – is accumulating strain that can trigger a great earthquake, he said. Historically, such events tend to occur, on the average, every 300 to 500 years.

Damage from an undersea earthquake as large as the one that shook the Indian Ocean could span from Northern California to Vancouver, B.C., Weldon said. He and his colleagues estimate that the resulting tsunami would add to the damage in the low-lying coastal part of the Pacific Northwest and extend beyond the region to as far away as Japan.

There is a geological record of the 1700 tusnami, according to Weldon. This includes widespread evidence of submerged coastal estuaries (the wide mouths of rivers), marine fossils and sand deposits carried by the tsunami far up coastal rivers, and drowned coastal forests. Chemical dating and tree ring analysis established that most of these forests were drowned in the winter of 1699–1700.

Weldon, who has lived in Indonesia and has relatives in Thailand, said last weekend’s tragedy brings home the need for coastal residents and tourists to learn about and take precautions against tsunamis.

“For an earthquake as strong as the one that hit southeast Asia, the shaking at the Oregon coast would last for up to 90 seconds and be great enough to cause significant damage and loss of life,” he said. “Most significantly, a tsunami will arrive at the coast as soon as minutes following the shaking to within a half-hour.”

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