BELLINGHAM, Wash. -- Scientists studying the effects of a future massive earthquake off the Washington Coast have learned that it could produce devastating tsunamis along the far northern Washington waters along the Salish Sea.
Studies have shown partial ruptures along the Cascadia subduction zone off the Pacific Northwest Coast and ensuing large destructive quakes and catastrophic tsunamis happen roughly every 300-500 years (the last one happening in January, 1700. )
But this study calculated the worst case scenario of a massive rupture along the entire length of the Cascadia subduction zone that would trigger a 9.0 quake and how it would affect the greater Bellingham and Anacortes areas. Scientists have determined these type of events happen every 1,800-4,500 years (or an average of about 2,500 years.)
That scenario indicates the first tsunami waves would reach the Anacortes/Bellingham areas about 1.5 hours after the Cascadia earthquake, with water as deep as 18 feet and rushing in and out at a speed of 20 knots (23 mph), especially near Guemes Channel, Burrows Pass, off Clark Point and off Eliza Rock . Tsunami inundation is expected to continue for more than 8 hours. That's on top of any earthquake damage.
Researchers admit the model assumes greater inundation than previous modeling "so communities can plan for worst outcomes."
MORE | Read the full study
The study produced two maps for both the Bellingham area and the Anacortes area. One is based on survival criteria for those caught outside when a tsunami arrives. Waves below 2.5 feet (denoted as yellow areas) are survivable if you can get indoors or avoid the direct force of the wave by standing in the leeward side of a tree or power pole. Between 2.5 and 6 feet (light orange), it's unlikely to survive if outdoors, but odds improve if you can get on a roof or inside a multi-story building. Tsunamis above 6 feet (denoted as dark orange on the map) would be difficult to survive in any circumstance if caught in the open, unless you can find a reinforced structure or vertical evacuation structure, the study concludes.
The other maps show the total depth the model calculated of tsunami inundation in this scenario.
Bellingham Maps: Total water inundation | Tsunami height by survival criteria
Anacortes Maps: Total water inundation | Tsunami height by survival criteria
"Earthquakes and tsunamis are very real threats that we must be proactive in preparing for,” said Commissioner of Public Lands Hilary Franz. “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 study also produced maps that suggest where the greatest tsunami inundation would occur, although the study's authors warn that due to model limitations, it should be used to guide overall evacuation planning and not site-specific tsunami mitigation planning.
In the event of Cascadia subduction quake, tsunamis would also inundate the coastal waters and other inland waters of Washington as well. This study just focused on the Bellingham and Anacortes areas.