In the worst-case scenario, the tsunami would come so fast and so suddenly that residents in some areas would have very little to no time to evacuate.
The projections are based on new simulations the DNR shared on its website this week.
Corina Allen, chief hazards geology chief for the agency, is among those working on the detailed simulations of what might happen if a major earthquake strikes in the Cascadia Subduction Zone, a 621-mile fault line that runs offshore from Northern Vancouver Island to Cape Mendocino, California.
“The highest modeled inundation so far has been in southwest Washington at Damon Point, and there’s expected to be about 60 feet of flooding above the previously dry surface,” Allen told KOMO-TV.
Neighborhoods in Seattle and Tacoma could also be flooded, although they would have more time to evacuate.
“We hope these simulations can really help people to plan for those events before they happen,” Allen said.
Tsunamis most often happen when a large earthquake occurs under the ocean or near the shoreline, pushing sea water upward into a wave that grows as it spreads over shallow water, according to the DNR. Earthquakes that generate tsunamis are usually 7.0 magnitude or higher and are centered less than 62 miles below Earth’s surface.
The new simulations use a magnitude 9.0 earthquake as the triggering event, which then creates a tsunami that could travel as fast as 500 mph over water and crash onto land with waves up to 20 feet high. The coastal areas, in turn, would have already subsided due to the earthquake.
The last earthquake that big in the Cascadia Subduction Zone struck in 1700, according to the Pacific Northwest Seismic Network. Geological evidence shows that such large earthquakes have happened in the zone at least seven times in the past 3,500 years, or about every 400 to 600 years.
Officials hope the simulations will serve as a wake-up call for local governments and residents.
“We know tsunamis will hit our state. It’s a question of when, not if, which means we need to prepare now,” Washington Commissioner of Public Lands Hilary Franz told KPTV. “Our hope is that these stark videos drive home the need for communities to take action to become more secure and resilient.”