Washington State Department of Natural Resources Releases New Tsunami Maps

The state continues to prepare for the big magnitude 9.0 quake and ensuing tsunami.

by Jim McKay / July 6, 2018

A Cascadia Subduction zone earthquake scenario involving a magnitude 9.0 quake in the state of Washington would most likely trigger a tsunami that could have devastating effects. Estimates are that it could kill more than 10,000 people and injure 30,000 more.

The last similar quake to hit the area did so around January 1700 and the next one could hit at any time. It could be tomorrow or in 200 years, and that’s what makes preparation so hard. But it’s necessary.

Part of the preparation by the State Department of Natural Resources (DNR) is to develop maps that show where a tsunami inundation would be and the wave speed. Estimates are that residents would have an hour to 90 minutes to get to higher ground and that the tsunami could continue for eight hours or more. The models indicate that the tsunami could reach 18 feet in height at speeds up to 20 knots.

The models use a wave height of 12 feet for planning purposes and studies indicate waves in most areas will be under 10 feet.

The maps are specific to parts of Washington, the Northwest, and it is hoped local county, city and tribal officials will use the maps to better prepare residents.

DNR Communications Manager Joe Smillie said the maps were based on a near-worst-case scenario of an approximately 2,500-year event for planning purposes and to measure against design requirements and building codes.

“We are also producing some walking maps that will be distributed around the communities, so people can see where go to during a tsunami,” Smillie said. The walking maps or assembly maps will eventually be posted in public places and the county will also install evacuation route signs in at-risk communities and designated assembly areas.

Those assembly areas are parking lots or open fields that can serve as meet-up areas for residents and first responders can go to plan and stay safe. “Depending on how bad it is, they may have not home to go back to … or it may be condemned from damage, even if it’s still standing there,” Skagit County Department of Emergency Management Director Doug ten Hoopen told the Skagit Valley Herald.

The shaking from a magnitude 9.0 earthquake would last for several minutes and when it stops, the water along the shorelines would retreat slowly and drop several feet before tsunami waves would rush in some two hours later.


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