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In predicting earthquakes, what do we really know about the next ‘big one’?

How much do we really know about forecasting a massive earthquake off the Washington Coast?

Geologists will admit that they are a little fuzzy on the details of how often earthquakes hit our region and how large they can be. They just know that a big one hits every few hundred years.

The uncertainty stems from the fact that our history really only dates back to Lewis and Clark. There just isn’t a good recorded history of Northwest earthquakes.

University of Washington researcher Brian Atwater is trying to get a better handle on forecasting earthquakes based on the historical record left on the ocean floor about 100 miles offshore, in what is known as the Cascadia subduction zone.

“Our paper calls into question some of the approaches that have been used to extract earthquake history from those sedimentary archives,” said Atwater.

He dusted off research that oceanographers completed at the University of Washington four decades ago to see if it matched the current understanding of earthquake forecasting.

Atwater said the results of core samples those researchers completed were forgotten and just sitting around the school.

“Most of the information is really tied up in the older cores,” he said. “We felt it was important to go back and make sure that the findings about earthquakes, based on offshore information, would be consistent with what was seen back in the 60’s and 70’s.”

His research doesn’t question the understanding that the fault off the Washington Coast is active and capable of creating a massive earthquake about every 500 years.

“Nobody disagrees about the faults having a long history of very big earthquakes and associated tsunamis,” he said. “It’s just the details of the numbers we’re talking about.”

Atwater said the goal is to make sure that earthquake research and the models based on it are as accurate as possible and that the geologic evidence is being interpreted properly. “The sharper your vision of that history, the clearer your view of what lies ahead,” he said.

The last major earthquake to hit the fault off the Washington Coast was in January of 1700. It created a tsunami that traveled across the Pacific Ocean and was registered in Japan. It was also recorded in the Native American oral history in the Pacific Northwest.

Scientists say big ones like that have hit the region seven times in the last 3,500 years.

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