Major earthquake could produce tsunami waves that could swamp Seattle in minutes

The new study used newer data on topography and elevation, spanning a larger area, than previous studies of the Seattle, Tacoma and Everett areas published in 2003, 2009 and 2014. While Tacoma is projected to see less water inundation than in previous studies, the new report said waves could travel farther inland. North of Deception Pass, the waves grow smaller, to a projected average height of 5 feet (1.5 meters).

Franz urged residents to learn more about the risks in their area, sign up for earthquake and tsunami warnings, and to prepare an emergency kit with at least two weeks of water, food and other necessities — and to do all of that now.

In the study, researchers from the department’s Washington Geological Survey division used projections modeled after the last major earthquake under the Seattle fault — a magnitude 7.5 about 11,000 years ago — to estimate the height, arrival time and inland reach of a subsequent tsunami if, or when, the disaster repeats itself.

Research shows the fault has triggered smaller quakes, mostly around 6.5 magnitude, five times in the past 3,500 years. The quake that happened 11,000 years ago was likely the biggest in the past 16,000 years.

While it’s likely future earthquakes will be smaller than what was modeled, the projections were still “shocking,” said Alex Dolcimascolo of the Geological Survey division, an author of the report. “We really wanted to emphasize this scenario so people can prepare.”