SEATTLE — State officials released new information about what a tsunami produced by a major earthquake on the Seattle Fault could do to Seattle and Puget Sound.
The study prepared by geologists from the Washington Geological Survey division of the Department of Natural Resources, was done to help local and state emergency departments prepare for a tsunami in the Seattle area.
“The Seattle Fault crosses east-west through Puget Sound and downtown Seattle and has produced several earthquakes documented in the geologic record throughout the region,” a news release about the report said.
The report finds that tsunami waves would reach shorelines in fewer than 3 minutes in many places along the eastern side of Bainbridge Island, Elliott Bay and Alki Point.
It also shows that flooding could exceed 20 feet along shorelines in the greater Seattle area. Flooding and strong currents may continue for more than 3 hours from the start of the earthquake, according to the report.
Experts acknowledge the chance of that happening is very small, but it’s enough of a possibility that Department of Natural Resources geologists conducted their own study.
“The last known earthquake on the Seattle Fault occurred about 1,100 years ago. However, geologic evidence shows five additional earthquakes of an estimated magnitude 6.5 occurred within the Seattle Fault zone during the last 3,500 years,” a news release from the Washington State Department of Natural Resources said.
The Seattle Fault crosses east-west through Puget Sound and downtown Seattle.
“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.”
While the study found the 6 feet of flooding at the Port of Tacoma would be lower than in previous studies, it also found that waves may travel up to 3 miles inland in parts of the port.
While flooding from the tsunami would be greatest closer to the Seattle Fault, the study showed shoreline flooding and increased currents throughout the Salish Sea, from Blaine to Olympia.
The earthquake scenario used for the study was for a very large, low-probability magnitude 7.5 earthquake, which produces the maximum-considered Seattle Fault-generated tsunami for emergency planning purposes.
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