Earthquake would trigger 20ft tsunami in Seattle in 3 minutes, state report says

Nicholas Turner/The Seattle Times

A tsunami triggered by a major earthquake beneath Puget Sound would arrive at our shores sooner and reach farther inland than previously thought, according to a study released Thursday by the state Department of Natural Resources. from Washington.

Models showed that a tsunami following a magnitude 7.5 quake would flood Seattle’s shoreline in more than 20 feet of water and reach parts of Bainbridge Island, Elliott Bay and Alki Point within 3 minutes.

Waves could reach a staggering 42 feet at the Seattle Ferris Wheel and reach Lumen Field and T-Mobile Park.

“Three to five minutes is all that separates a seismic event from the arrival of tsunami waves,” Public Lands Commissioner Hilary Franz said Thursday at a news conference on Seattle’s waterfront. . “That’s why we’re conducting this research now so that everyone is aware of this, so that our local government is aware of this, and we can start preparing and planning and taking all the necessary precautions.”

The new study used more recent topography and elevation data, covering a larger area, than previous studies of the Seattle, Tacoma and Everett areas published in 2003, 2009 and 2014, respectively.

While Tacoma is expected to see less water flooding than in previous studies, the new report indicates that the waves could travel farther inland.

Water along parts of Harbor Island’s northeast coast could rise 15 feet, the study showed, while waves could reach up to half a mile inland, from Smith Cove at Sodo, and nearer a mile near Tacoma Harbor.

North of Deception Pass the waves get smaller, up to a projected average height of 5 feet.

Franz urged residents to learn more about the risks their area faces, sign up for earthquake and tsunami warnings and prepare an emergency kit with at least two weeks’ worth of water, food and other necessities – and to do it all now, before it’s too late.

“We won’t be able to eliminate all risk from earthquakes and tsunamis, but we can use this new modeling to help us develop plans to ensure our resilience when it happens,” she said.

In the study, researchers from the department’s Washington Geological Survey Division used projections modeled after the last major earthquake below the Seattle Fault – a magnitude of 7.5 that occurred about 1,100 years ago – to estimate the height, arrival time and inland range of a subsequent tsunami if, or when, the disaster repeats itself.

Research shows the fault has triggered smaller earthquakes, mostly around magnitude 6.5, five times in the past 3,500 years.

The earthquake that occurred 1,100 years ago was probably the largest of the last 16,000 years.

Although future earthquakes are likely to be smaller than what was modeled, the projections were still “shocking”, said Alex Dolcimascolo of the Geological Survey Division, author of the report. “We really wanted to emphasize that scenario so people could prepare.”