Washington State’s earthquake and tsunami risks compare to Japan’s

The Cascadia Subduction Zone (where one tectonic plate sinks beneath another) is capable of very large earthquakes of magnitude 9.0 or greater.

The rumbling sound and violent shaking are followed by the roar of the ocean as a powerful tsunami inundates the countryside washing away nearly everything in its path. That’s what occurred on March 11, 2011, when an earthquake and tsunami struck northern Japan, but we could also be talking about Western Washington on January 26, 1700, when a powerful earthquake in the Cascadia Subduction Zone occurred just off of the state’s coast. The geologic record indicates that the magnitude of the 1700 earthquake was between 8.7 and 9.2, strikingly similar to Japan’s 8.9 magnitude earthquake last year. 

As we approach the one-year anniversary of the Tohoku earthquake, residents of Washington State should know that a similar-sized earthquake followed by a large tsunami is primed to occur here. Washington State has a similar subduction plate scenario in which the tectonic plates lock together, build up pressure, and eventually release, causing a powerful earthquake and, quite possibly, a substantial tsunami. This event has been predicted to recur at an interval of 300-500 years; however, an earthquake can occur at any time. Our last great earthquake was in 1700 and we can expect another either any day or not for another century. 

DNR’s Division of Geology and Earth Resources helps Washington State residents prepare for disasters, such as earthquakes and tsunamis. The Division is also part of the state’s response. Following a geologic disaster, the Washington Military Department’s Emergency Management Division (EMD) works closely with the Division of Geology and Earth Resources to evaluate the extent of the disaster and help advise local emergency management agencies of potential threats and recommended evacuations.

As an example, DNR and EMD went into action when a 4-foot tsunami wave was forecasted to hit portions of the Washington State coastline following the Tohoku earthquake. Acting with DNR’s input, EMR recommended evacuations of Pacific Beach, Moclips and Taholah. In addition, Neah Bay and healthcare facilities in Long Beach also voluntarily evacuated. Fortunately, the waves experienced in Washington last year were minor. But as you watch the media reports looking back to last year’s tragedy in Japan, please remember: it will someday happen here again, too.

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