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Tsunami waves would reach Seattle within minutes after earthquake, study finds

Washington state officials urged Seattleites to be prepared for a tsunami, even though the last known earthquake on the Seattle Fault occurred about 1,100 years ago.

SEATTLE — Tsunami waves from a magnitude 7.5 earthquake on the Seattle Fault would only take minutes to reach the greater Seattle area, according to a newly released study.

The Washington State Department of Natural Resources (DNR) released the new study Thursday and urged Seattleites to be prepared, even though the last known earthquake on the Seattle Fault occurred about 1,100 years ago.

“Although the chances of this happening in our lifetime is low, it's important for families to get prepared now,” said Maximilian Dixon, the hazards and outreach program supervisor for the Washington Emergency Management Division. “The ground shaking will be your warning that a tsunami may be on the way. Make sure you know where the closest high ground is and the quickest route to get there."

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Tsunami waves would reach the shoreline in less than three minutes in many places on the eastern side of Bainbridge Island, around Elliott Bay and Alki Point, according to the study prepared by geologists within the Washington Geological Survey division of DNR.

The study also found flooding from such a tsunami would exceed 20 feet along Seattle's shoreline. The DNR said the study found waves may travel up to 3 miles inland at the Port of Tacoma, although flooding would be lower than in previous studies.

Flooding from the tsunami will be greater near the Seattle Fault but the new study showed shoreline flooding and increased currents throughout the Salish Sea, from Blaine to Olympia. 

The earthquake scenario used in the modeling is a "very large, low-probability" magnitude 7.5 earthquake on the Seattle Fault, which runs east-west through Puget Sound and downtown Seattle. The fault has produced several documented earthquakes, according to DNR.

The DNR said the model does not account for tide stages or local tsunamis triggered by earthquake-induced landslides.

“Most often, when we think of tsunamis, we think of our outer coast and communities along the Pacific Ocean. But there’s a long history of earthquakes on faults in the Puget Sound,” said Commissioner of Public Lands Hilary Franz. “While the history of earthquakes and tsunamis along the Seattle Fault is less frequent than the Cascadia subduction zone, the impacts could be massive. That’s why it’s critical these communities have the information they need to prepare and respond.”

The study was conducted to help local and state officials develop response and preparedness plans for a tsunami.

The DNR offers many resources for families to be prepared in the event of an earthquake. If an earthquake occurs, it's safest to drop, cover and hold on, and then evacuate to higher ground to get as far inland as possible.

“We will continue to ensure our Office of Emergency Management -- and all our departments -- are best equipped to respond to emergencies and natural disasters, while we also strengthen our infrastructure and build a resilient city now and for the future," said Seattle Mayor Bruce Harrell.

The most recent earthquake was powerful enough to move the beach at Restoration Point on Bainbridge Island upward by 23 feet and dropped land at Seattle's West Point by 3 feet.

DNR said the next earthquake may establish new shorelines in many locations near the fault line.

For more information and resources, visit dnr.wa.gov/tsunami.


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