Washington state’s coastal communities are well aware they’re just moments away from a tsunami following a major earthquake. Bright blue evacuation signs that abound near beaches and trailheads serve as reminders to head for higher ground when the landscape rumbles whether it’s along the Cascadia Subduction Zone that stretches from Northern California to Vancouver, British Columbia, or a distant earthquake fault across the Pacific.
What has been less clear is just how the surge could go about inundating the inland shores of Seattle, Tacoma, Bellingham, and other Washington cities tucked amid the islands, bays, coves and canals of Puget Sound, home to roughly 5 million people, as well as the communities along the greater Salish Sea that connects the state with British Columbia to the north.
New digital simulations from the state Department of Natural Resources’ Washington Geological Survey demonstrate the projected intensity of a fast-moving wall of water in the minutes and hours following a magnitude 9.0 megaquake on the Cascadia fault. Color coding identifies the wave peaks and troughs and shows how the surge is most likely to crash through the region based on the geology of the ocean floor and other factors.
Though the simulation tempers itself with the description “wave peaks of 10 feet or higher,” previous models mapped by DNR, the National Oceanic and Atmospheric Administration, and the Federal Emergency Management Agency have predicted wave peaks up to five stories tall, or 50 to 60 feet. Debris is still washing up along the West Coast following the 2011 magnitude 9.1 earthquake and tsunami in Japan that killed at least 20,000. There, the wave peak topped out around 33 feet.
More detailed simulations of individual areas considered at highest risk are to be released over the next three years as part of Washington’s continued efforts to prepare for forthcoming natural disasters as a member of the National Tsunami Hazard Mitigation Program. It’s been about 300 years since the Cascadia fault last ruptured so dramatically, and scientists say the region is due for its next big quake.
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