Should a great earthquake occur along the Cascadia subduction zone, Belingham residents theoretically may have only an hour and a half to prepare before an 18-foot-high wall of water from a resulting tsunami arrives, according to a study released Monday by the Washington State Department of Natural Resources.
The state DNR published new maps showing the potential impacts to communities on the north Salish Sea from a tsunami generated by a magnitude 9 earthquake along the Cascadia subduction zone — an event that geologic history shows can occur approximately every 2,500 years and one that current building codes now prepare for in the region, according to a DNR release.
“Earthquakes and tsunamis are very real threats that we must be proactive in preparing for,” Commissioner of Public Lands Hilary Franz said in the release. “That’s why DNR’s team of highly-trained geologists works each day to ensure our communities have the information they need to prepare and be safe.”
The DNR model predicts tsunami inundation could reach the Bellingham/Anacortes area about 90 minutes after the earthquake and continue for more than eight hours. Inundation depths could be as high as 18 feet with velocities of 20 knots in some areas.
"We knew that it could produce tsunami waves — we've seen that from past events," DNR Communications Manager Joe Smillie said. "But we didn't know to what extent and magnitude."
While this is a worst-case scenario, the study predicts wave heights of a potential tsunami will average "less than 10 feet for most areas." Within Whatcom County, 12 feet is the wave height used for planning purposes, according to a press release from the Whatcom County Sheriff's Office in response to the study.
The modeling, which did not include updates for other coastal areas in northern Whatcom County, has already been sent to city, county and tribal governments to help with emergency planning, Smillie said.
"The Whatcom County Sheriff's Office considers the protection of the citizens of Whatcom County paramount," Sheriff Bill Elfo said in his office's release. "With the release of this new study, we now have another data point to use in the development of updating of the Whatcom County Tsunami Action Plan."
Elfo also noted that eight tsunami sirens have been installed between Point Roberts and Squalicum Harbor since 2006, and a ninth is being installed this summer.
Smillie said he hopes the model provides information everyone can store away, especially with other faults in the area that can produce smaller tsunami that could still impact Bellingham.
"I hope they can look at it and file it away in the back of their brain as a piece of information for just in case that big quake does hit and there are tsunami warnings," Smillie said. "They'll know if that does happen to grab a few things and head uphill. ... It's good to have water and clothes in a go bag and have it ready to go in your house."
Elfo said the sheriff's office will help review the area's tsunami action plan during a region-wide catastrophic earthquake exercise in 2021, including a week-long, full-scale exercise to simulate the effects of a tsunami and the regions ability to respond.
"Tsunami resilience of our coastline cities, residences and businesses is an extremely important role for local emergency planners," City of Bellingham Interim Emergency Management Coordinator Bob Vander Yacht said in the sheriff's office press release. "Priority one for planning is the safety of Whatcom County citizens and visitors."