Report says tsunami triggered by Puget Sound earthquake would hit Seattle in minutes

The Washington State Department of Natural Resources (DNR) released a new study on Thursday, showing how a tsunami produced by a major earthquake in Puget Sound would impact the greater Seattle area.

The DNR and the Washington Geological Survey conducted this study to develop local emergency response and preparedness plans to ensure the highest populated area in the state is ready in case a tsunami hits. The study shows the potential aftermath of a tsunami triggered by a 7.5 magnitude earthquake along the Seattle Fault zone, which crosses east and west through the Puget Sound and downtown Seattle.

(The Washington State Department of Natural Resources)

According to the study, tsunami waves would reach the shoreline in many places on the east side of Bainbridge Island, Elliott Bay and Alki Point in less than three minutes. In addition, a tsunami will likely create flooding and inundation lasting more than three hours, reaching greater than 20 feet along the shoreline in the greater Seattle area. 

The study also suggests that tsunami waves would create flooding that is six feet deep, traveling up to three miles inland in parts of the Port of Tacoma.

While flooding from the tsunami will be the greatest closer to the Seattle Fault zone, the study shows the potential for shoreline flooding and increased currents throughout the Salish Sea, from Blaine to Olympia.

Experts say the last known earthquake to happen in the Seattle Fault happened about 1,100 years ago. Geological evidence shows that it was powerful enough to thrust the beach at Restoration Point on Bainbridge Island upward by 23 feet, while dropping land at Seattle’s West Point by three feet. If another earthquake happens, the study suggests that the land level changes could create an entirely new shoreline in many locations near the Seattle Fault zone. 

Despite the major time gap since the last earthquake, Scientists say another earthquake is still possible. Geological evidence shows there were five additional earthquakes averaging a 6.5 magnitude in the Seattle Fault zone in the last 3,500 years. 

"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. Get signed up for tsunami and local alerts."

"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."

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According to Seattle Mayor Bruce Harrell, studies like this are a critical tool for the city to understand risks and prepare for future emergencies.

"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 Mayor Harrell.

Officials say if you feel an earthquake drop, cover, and hold on, then evacuate to high ground and get as far inland as you can as quickly as possible.