Saturday, November 14, 2015

When will a massive earthquake, tsunami hit the Pacific Northwest?

by David Martin

SEATTLE – Walking down almost any street in Seattle’s historic downtown, Eric Holdeman sees danger.

Holdeman ran the King County Office of Emergency Management for 11 years. He doesn’t think the area around Pioneer Square would do well in a powerful earthquake.

“These buildings would likely pancake,” said Holdeman, who now has his own consulting business. “The walls separate and the floors fall down. We’re talking about, like, the Haiti earthquake, where you see structures completely collapsed right on top of one another.”

For Holdeman, geologists and emergency planners, it’s not a question of if a major earthquake will strike the Pacific Northwest, but when. 

The Cascadia subduction zone, a 700-mile geological fault off America’s Northwest coast, has produced a magnitude 9.0 earthquake every 300 to 500 years. It’s been 315 years since the last one. 

A map of the Cascadia subduction zone.

“Certainly, we’re back in that window,” Holdeman said.

As regional director for the Federal Emergency Management Agency (FEMA), Kenneth Murphy would head the federal response to a Cascadia subduction zone disaster. He told America Tonight a magnitude 9.0 Cascadia subduction zone earthquake and tsunami would result in thousands of deaths and millions of homeless.

“I think people are just not mentally or physically prepared to think about how bad something like that can be,” Murphy said.

In Seattle, Holdeman said government officials have done little to mitigate the risks posed by old brick buildings. The city has about 800 unreinforced masonry buildings, he said.

“I don't think this state is going to take seismic safety to an appropriate manner until we're dragging dead bodies out of buildings,” he said. “Unfortunately, it's the American way that we don't address issues until we've been impacted by whatever that disaster is.” 

‘Destroys everything’

A couple hours southwest of Seattle, along the flat, scenic Washington coastline, Chuck Wallace also worries about “the big one.”

“The Cascadia subduction zone earthquake is supposed to be about a 9.0, maybe 9.1 earthquake, which is going to rock and roll everything around here for three to five minutes,” said Wallace, the deputy director of Emergency Management for Grays Harbor County.

He said the violent shaking would collapse bridges and overpasses, crack roadways and pipes and cause sandy soil to lose its strength in an otherworldly process called liquefaction.

Still, it’s what comes after the earthquake —a tsunami — that worries Wallace most.

“They believe the biggest tsunami wave we are going to have is 22 feet in this area here,” said Wallace in an interview in the fishing and tourist town of Westport. “However, there’s plus or minus 30 percent on that, so it could be 30 feet high. And you not only get one wave, you get multiple waves.”

Walking to the top of Westport’s three-story beachfront observation tower, Wallace pointed out why tsunamis are so dangerous along the Washington coast. The land stretching from the ocean is flat, and the key to surviving a tsunami is reaching high ground.

“The problem that they have here in Westport is that there is no real high ground,” said Wallace, adding that the concrete observation tower itself would not survive a tsunami.

To make the situation even direr, Wallace said the earthquake would likely make the roads impassible by car, meaning people will need to walk to safety. The math is not encouraging: The first tsunami wave would make landfall in 15 to 30 minutes, yet much of Grays Harbor County is a 40- to 50-minute walk to higher ground.

“You’re going to have two, three, four waves,” Wallace said. “The second wave is going to take the debris that was created from the first wave and now that becomes a battering ram for the second one. So, it starts banging into walls and destroying more property. Cars become battering rams; trees, everything becomes a battering ram and just destroys everything in its way.”

‘Very bad effects’

Geologists now fear an enormous earthquake, because the North American plate and the Juan de Fuca plate are stuck together at the Cascadia subduction zone. The North America plate wants to move west 13 feet a century above the Juan de Fuca plate, but it has been going nowhere. Every year the plates are stuck, the pressure builds.

“When they suddenly get unstuck, you can get a very big earthquake,” said Brian Atwater, a geologist with the U.S. Geological Survey in Seattle.

The chance of this happening in the next 50 years is 1 in 10, according to “Cascadia Subduction Zone Earthquake: A Magnitude 9.0 Earthquake Scenario,” a document produced by the FEMA and the Cascadia Region Earthquake Group.

According to the report, the death toll of in a worst-case earthquake and tsunami scenario could exceed 10,000, with more than 30,000 injured. It would also have an economic impact of $70 billion across California, Oregon and Washington.

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