Washington officials already have concluded the state is woefully unprepared for a catastrophic earthquake, like the so-called “Big One” that’s expected to strike near the coast sometime in the next few centuries.
But earthquakes can do damage from afar, too. After a powerful undersea quake and a blast of cellphone alerts early Tuesday, Alaskans braced for a tsunami that was expected to smash into the state’s southern coast and western Canada. The National Weather Service also issued lower-level watch advisories for Washington, Oregon, California and Hawaii.
While the killer wave never materialized, it was a reminder that Washington needs a better understanding of how tsunamis big and small could impact the state’s coastal communities, said Corina Forson, the chief hazards geologist for the state Department of Natural Resources.
DNR’s inundation maps, which illustrate areas subject to tsunami flooding, are incomplete and outdated, Forson said. And they’re based on earthquakes that might strike close to home – along the Seattle Fault and in the Cascadia Subduction Zone, for example. They don’t model what would happen if, say, the Gulf of Alaska quake really did generate a far-reaching tsunami.
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“We really only have about half of all Washington’s coastline mapped for tsunami hazards, and none of that really is for these distant events,” Forson said.
DNR says Washington is the only West Coast state that does not have a thorough, up-to-date analysis showing which critical infrastructure is at risk. The agency is asking lawmakers for $543,200 in startup money, plus $493,200 per year, to hire two geologists and a technician dedicated to earthquake and tsunami mapping.
“We’ve asked for this for several years and have not got much traction,” said Joe Smillie, a DNR spokesman. “It got into the governor’s budget now, so that’s encouraging.”
Tuesday’s magnitude-7.9 earthquake struck shortly after midnight and triggered a series of aftershocks. It sent Alaskans racing to evacuation centers in Kodiak and other coastal towns, and the shaking was even felt in Anchorage, some 350 miles from the epicenter. The tsunami warning was lifted after about four hours. Remarkably, no damage or injuries were reported.
The earthquake started in a subduction zone in the Gulf of Alaska, where a tectonic plate that forms the floor of the Pacific Ocean is slowly sliding underneath the North American continent. It’s the same zone that in 1964 produced the second most powerful quake ever recorded, along with deadly tsunamis.
Forson said Tuesday’s quake probably didn’t cause a tsunami because of how the plates moved underwater, grinding horizontally rather than forcing one plate upward.
“We usually see tsunamis from reverse faults and not these strike-slip faults, unless there’s a landslide or something associated with it,” she said. “But because the magnitude was so large, that automatically triggers a warning.”
Any earthquake below a magnitude 6, she said, is analyzed by federal scientists before tsunami warnings are issued. With larger quakes, tsunami centers play it safe and let the warnings go out automatically.
“These tsunami waves travel so fast across the ocean, you don’t have a lot of time to really go into detail and assess the earthquake parameters,” she said. “It’s better to get a warning or a watch out, so that people have time to react and evacuate if necessary.”
Forson said people should seek high ground immediately if they feel an earthquake near the coast. Although resources are strained, emergency managers in Western Washington do plan for such events.
“All of the major population centers on the outer coast do have sirens and evacuation routes,” Forson said.
She urged people to sign up for cellphone notifications with the U.S. Geological Survey and the National Weather Service.