Major Oregon quake believed more likely

PORTLAND — Geologists now say there is a 10 to 14 percent chance of a major earthquake and tsunami hitting the Oregon Coast within the next 50 years, putting the coast through a disaster like that Hurricane Katrina brought in 2005 to the South.

Instead of thinking such quakes take place about every 500 years, geologists say recent work indicates the range to be from 300 to 350 years — which represents what one official called a near doubling of the chances for a big quake.

"The amount of devastation is going to be unbelievable," said Rob Witter, coastal geologist with the Oregon Department of Geology and Mineral Industries. "People aren't going to be ready for this. Even if they are prepared, they are going to be surprised by the level of devastation."

The findings have brought new urgency to calls for preparation along the coast — for people to identify high ground and for families to draw up emergency plans.

"The geology and numerical models predict tsunamis could reach as high as 80 to 100 feet in Oregon, which is similar to the tsunami that struck Sumatra," Witter told The Oregonian newspaper. "We need to be very cautious and prepare for that event. It may not happen in a person's lifetime, but if it does, it's going to be equivalent to a Katrina-like event."

In about a generation, Witter said, scientists have changed their minds about the dangers posed by earthquakes from the Cascadia subduction zone. That is the area 50 to 75 miles out to sea where one tectonic plate is sliding under another.

Twenty-five years ago, they didn't think it could produce earthquakes.

But the work of Brian Atwater of the U.S. Geological Survey linked a "ghost forest" in a Washington state tidal marsh, thought to have been killed in a big quake, to a tsunami recorded in a Japanese historical document on Jan. 27, 1700.

Then Chris Goldfinger, director of the Active Tectonics and Seafloor Mapping Lab at Oregon State University, turned up new evidence of big earthquakes.

He studied offshore landslides along the 600-mile fault line. First he found 20 representing earthquakes of magnitude 9 or greater in the full zone over the last 10,000 years, and then he found 18 more of magnitude 8 to 8.5 in the southern part of the zone.

Witter said those findings put the cycle of giant quakes at 300 to 350 years.

Native Americans and other peoples have passed stories of big quakes from generation to generation, said James Roddey, spokesman for the state geological agency.

"They created a cultural tradition by retelling these events and legends," Roddey says. "We see that around the world. When the Sumatra earthquake struck (the Indian Ocean), the Andaman Islands were right in the middle of the rupture zone. There was huge ground shaking, but very few people died from the tsunami because they had also created this culture of awareness. They went to high ground. They survived the event."

Though the Sumatra and Cascadia subduction zones differ, Witter said, a tsunami at the Oregon coast would be much the same.


Information from: The Oregonian,

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