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Washington National Guard Rehearses For Cascadia Megaquake

The Washington National Guard -- joined by officers from Oregon and Idaho -- are preparing for a massive military relief effort.

More than 1,000 Washington National Guard members and state and county emergency managers across Washington rehearsed this week for a worst-case earthquake scenario -- a magnitude nine rupture of the offshore Cascadia fault zone.

Washington National Guard Adjutant General Bret Daugherty said he assumes quake relief in that case will need to be delivered by airlift from east of the Cascades.

"We're going to have large pockets of isolation because we're not going to be able to travel on the ground,” he said. “So really, help is going to have to flow into Western Washington from the east. Spokane is going to play a critical role there."

In the megaquake scenario this exercise simulates, the Washington coast is completely cut off by landslides, collapsed bridges and buckled roads. Helicopters might be the only way to get around. More of them will be needed though.

That's why the assistant adjutant general of the Idaho National Guard is here.

“I'm going to have to go back and say, 'Look, they're going to really need a lot of help,’” said Boise-based Brigadier General John Goodale. "When you see what a Cascadia event -- the earthquake -- would do to the state of Washington, that is probably the most eye-opening thing I saw.”

Goodale said if the electric grid goes down on a wide scale, the Boise airport might even be an initial staging ground to funnel relief to Washington and Oregon.

The military’s response plan for a magnitude nine earthquake envisions a massive national mobilization.

"Our estimates right now are somewhere between 50,000 to 80,000 (service members) potentially to have to show up here to really get things put back together,” Daugherty said.

In this week's disaster simulation called Evergreen Tremor, a lot of military assets were deployed merely on computer screens. Daugherty said a much larger exercise is planned next year. In it, Navy, Army and National Guard units from multiple states will physically deploy in response to a pretend Cascadia megaquake.

The fault zone expected to generate the next Big One lies underwater between 40 and 80 miles offshore. It stretches from Vancouver Island to Northern California.

The last full rip of the Cascadia Subduction Zone happened in January 1700. The exact date and destructive power was determined from buried forests along the Pacific Northwest coast and an “orphan tsunami” that washed ashore in Japan. Geologists digging in coastal marshes and offshore canyon bottoms have also found evidence of earlier great earthquakes and tsunamis. The radiocarbon dating of those events makes it possible to estimate the recurrence interval of Cascadia megaquakes. Those estimates vary slightly among government agencies and universities.

Washington National Guard planners accepted a U.S. Geological Survey timeframe that posits a destructive Cascadia  quake roughly every 300 to 500 years. "We're 15 years into that window," warned Daugherty.

Now semi-retired, Tom Banse covered national news, business, science, public policy, Olympic sports and human interest stories from across the Northwest. He reported from well known and out–of–the–way places in the region where important, amusing, touching, or outrageous events unfolded. Tom's stories can be found online and were heard on-air during "Morning Edition" and "All Things Considered" on NPR stations in Washington, Oregon, and Idaho.