OLYMPIA – The nearest high ground is one of the most important pieces of information for safely evacuating from an incoming tsunami.
These maps, produced by DNR’s Washington Geological Survey, show the time it would take to evacuate on foot from the tsunami inundations zones caused by a Cascadia subduction zone earthquake.
“We’ve seen around the world how devastating tsunamis are for coastal communities,” said Commissioner of Public Lands Hilary Franz, the elected official who leads DNR. “In the event of a tsunami, nothing is more important than knowing where to go to be safe and how long it will take to get there. That is why Department of Natural Resources’ geologists are making this life-saving information easily accessible for everyone who lives, works or plays along Washington’s coast.”
The maps are colored to indicate how many minutes it would take to walk to safety from the inundation zone, assuming a slow walking pace of 2.46 miles per hour – the same pace used to time urban cross walk lights.
Waves from a Cascadia earthquake-induced tsunami could reach coastal areas like Long Beach or Westport as soon as 15 minutes after the earthquake starts.
Effective walk times differ for communities based on their topography. For example, people at Cape Disappointment can safely walk to higher ground in as little as 15 minutes, while the walk to safety from Long Beach can take as long as 75 minutes.
319 years since Cascadia last quaked
The geologic record shows the Cascadia subduction zone – the offshore area where the Juan de Fuca tectonic plate is pulled under the larger North American plate – produces megathrust quakes about every 300 to 600 years.
These maps are modeled on a magnitude 9 Cascadia earthquake. The onshore and offshore geologic record shows the last big earthquake happened in 1700 creating a tsunami that hit all of the Pacific Nothwest and traveled across the ocean to Japan. By using the models for larger Cascadia events, the maps provide a scenario that is useful for smaller events as well.
Models, maps available online
The new pedestrian evacuation maps and maps for other communities are available through an interactive map on the DNR web site: https://www.dnr.wa.gov/programs-and-services/geology/geologic-hazards/tsunamis#preparation-and-evacuation.6
The interactive map also provides access to tsunami evacuation brochures for areas that do not have walk time maps yet.
Other information about impacts from earthquakes to Washington communities is available on DNR’s Geologic Information Portal at: https://geologyportal.dnr.wa.gov