Washington's Tsunami Zone Triggers Concern
tsunami meeting emphasizes preparedness
February 23, 2008
By Leif Nesheim
OCOSTA The December storm that downed trees and power lines, putting much of the Twin Harbors into darkness was just a taste of the devastation that would be caused by a killer tsunami.
“If anything was to be learned from the last storm, it’s be prepared,” said County Commissioner Al Carter to an audience of nearly 50 folks gathered at a tsunami workshop Thursday evening in Ocosta. The workshop was the latest in a series of presentations organized by the Washington State Division of Emergency Management.
“If we have the end-of-the-world earthquake, that’s why they call it the end of the world,” Carter said.
Help, when it gets here, will be a long time coming.
Just offshore is the Cascadia Subduction Zone, a 600-mile stretch of sea floor slowly sliding under the continental plate. Every 500 years or so, the friction building up from the slow-speed collision between pieces of the earth’s crust snap like a giant rubber band, said Brian Atwater, a geologist with the U.S. Geological Survey.
There’s plenty of conclusive geological evidence that massive tsunamis, triggered by such an earthquake, have repeatedly struck the region, he said. Layers of sand and ghost cedar forests in tidal flats are two such examples. The physical evidence also matches up with Native American oral history and written records in Japan of the last known major earthquake, Atwater said.
On Jan. 29, 1700, a 9.0 magnitude earthquake rocked the Pacific Northwest and triggered a tsunami that devastated the entire Pacific coast of Japan. It will happen again. The geologic record shows evidence of numerous similarly massive earthquakes, some occurring as little as 350 years apart.
There’s a one in seven chance that such an event will happen in a person’s lifetime, said Tim Walsh, a geologist with the state Department of Natural Resources Division of Geology and Earth Resources.
When it happens there will be no official warning, he said. The first thing will be several minutes of shaking so hard people will have a hard time standing up, Walsh said.
Once the shaking has stopped, people living in low-lying areas designated on maps, like the one above, put out by his department should immediately head to high ground, he said.
How high is high enough? It varies with the strength of the earthquake, the height of the waves and the topography of the ground. An earthquake of this magnitude will generate an 18-foot wave that will hit the coast in less than 45 minutes, though flooding akin to a fast-moving tide will start much sooner, Walsh said. That doesn’t mean an elevation of 20 feet will be safe, though.
The best bet: Check the map. Barring that, get to at least 50 feet of elevation. Don’t think about driving, you won’t get far.
Roads will be devastated by landslides, pavement will be compromised by ground that has liquefied, bridges will be destroyed. Trees and power poles will block streets. Getting out on foot will be the only chance, Walsh said.
For people living in areas like Ocean Shores, Westport and the Grayland plains, the only option may be to head to a tall, sturdy building still standing, he said. There are several such designated gathering points around the county.
And, there likely won’t be just one wave. There will be a series of waves lasting at least half a day. That’s why it’s a good idea to have an emergency pack ready to take along when evacuating.
On the Harbor, it will take longer for the first wave to hit, maybe an hour or more. It won’t be as high as the coastal wave but subsequent waves will pile water into the Harbor, causing them to stack up into a higher wave many hours later.
So, the “Big One” hits, people escape to the hills and a few days later the feds fly in to fix everything, right? Wrong.
“We’re not gonna be able to get here right away,” said George Crawford, earthquake program manager for the state Emergency Management Division.
In an event of this size, the whole region is going to be devastated. Seattle, with its millions of people, will take priority over isolated rural areas, Crawford said. Worse, rescuers will have to painstakingly clear a path to rural communities.
Power could, and likely will, be out for months, he said. Infrastructure including water and gas lines will be ruptured, he said. It will be up to local residents to help themselves and each other until outside help is finally able to arrive, Crawford said.
“I hate to say it, but the resources are gonna go where the most people are,” Carter said. “You’re gonna be on your own.”
That’s why its vital to start talking and planning locally. The earthquake and tsunami might not come within the lifetimes of anybody today, but if it does, Carter asked the audience, wouldn’t it be better to be prepared?
For more information about the tsunami workshop or to find out how you can begin a Map Your Neighborhood Program in your area, call Anne Sullivan at 249-3911. Information also is available online at www.co.grays-harbor.wa.us/info/DEM/index.htm or www.emd.wa.gov.