Undersea fault hints that Northwest flood could be larger

GRANTS PASS, Ore. – Scientists are just back from a monthlong research cruise in the Pacific Ocean off Washington state, where they were trying to find the stickiest point on a section of the Cascadia Subduction Zone, the huge undersea fault that breaks loose every few hundred years, generating a massive tsunami and earthquake.

Paul Johnson, a professor of geophysics at the University of Washington, was one of the principal investigators on the trip funded by the National Academy of Sciences. He said it will be some time before the data from deep-sea measurements of heat and gas emissions is fully analyzed, but preliminary indications are the strongest upheaval will be farther out to sea than previously thought, he said.

That is important because the farther out to sea that upheaval occurs, the bigger the tsunami, and the greater the damage on land from flooding, and the less damage on land from earthquake.

The subduction zone runs from Cape Mendocino, Calif., to Vancouver Island, B.C. It is the place where the rocky plate underneath the Pacific Ocean pushes under North America. It last gave way on Jan. 26, 1700, generating a magnitude 9 earthquake and a tsunami that washed away houses in Japan, said Brian Atwater, a geologist at the U.S. Geological Survey in Seattle who investigates geological evidence stretching back thousands of years of subduction zone quakes.

“Paul is trying to figure out how big the tsunami can be,” said Atwater, who was not part of the research team. “In deep water, the tsunami generation can be especially effective. And Paul was out there in deep water.”

A study commissioned by the Oregon Legislature has estimated that more than 10,000 people could die and $32 billion in property could be damaged when the next one hits.

The data will be publicly posted on the Internet in coming months for anyone to access and analyze, Johnson said.