Southwest Washington Tsunami Inundation Hazard Maps Released

Southwest Washington Tsunami Inundation Hazard Map
Previous inundation mapping was based upon the last Cascadia Subduction Zone earthquake from 1700 AD. This new study and modeling is based upon a simulated 2500 year event, from a magnitude 9.0 earthquake. Photo courtesy: Grays Harbor County Emergency Management

Submitted by Grays Harbor County Emergency Management

Washington State DNR released new Tsunami Inundation Hazard Maps for Southwest Washington on Monday, March 26th, 2018. These maps are a bit different than previous tsunami inundation mapping. Previous inundation mapping was based upon the last Cascadia Subduction Zone earthquake from 1700 AD. This new study and modeling is based upon a simulated 2500 year event, from a magnitude 9.0 earthquake. This event produces a farther reaching tsunami inundation scenario.

Although the 2500 year event brings more tsunami inundation, the response from all people along the coast is the same.

  1. Once you feel the earthquake, DROP, COVER and HOLD ON until the ground shaking stops and then move to high ground immediately, whether it is a multi-story home, business, tower, or up a hillside. DO NOT attempt to run from the interior of a building during the earthquake as it increases your chances for injury. Always wait until the ground stops shaking. Remember, there WILL be aftershocks. DO NOT leave your place of safe haven unless someone in authority tells you it is ok to leave. You should stay in place for at least 2 full tidal cycles. (nearly 24 hours)

     ** Aftershocks may produce additional tsunami waves in coastal areas

  1. The first tsunami waves (a minimum of 4 are expected) will arrive within 15-25 minutes following the quake.
  2. Wave heights along the beaches will vary depending on the bathymetry of the coastline however the amount and level of inundation is our greatest concern. WA State DNR provided Grays Harbor Emergency Management some approximate inundation depths for this 2500 year event for our coastal areas.

Ocean City:
Screamin’ Eagle Campground: 45.1 ft.

Ocean Shores:
Spinnaker Park: 28.5 ft.
Bill’s Spitt (Peninsula Ct SE): 4.7 ft.
Elks Lodge: 21.1 ft.
Point Brown Ave at E Chance a La Mer NE roundabout: 27.2 ft.

Westport:
Westport Viewing Tower: 12.5 ft.
W Ocean Ave roundabout: 18.4 ft.
Westport City Park: 6.5 ft.

Grayland:
Beachcomber Grocery and Deli: 26.2 ft.
Security State Bank: 22.2 ft.

Areas of deepest on-land inundation
North Jetty (Ocean Shores): 67 ft.
Damon Point (Ocean Shores): 61 ft.
Ocean City: 57 ft.

Points to Remember

This is a model of a predicted event. There is a possible difference of +/- 30% to 40%, of the values in this study. Mankind has never been able to predict the timing of an occurrence, size of the earthquake or devastation caused by an earthquake and the possible resulting tsunami.

The modeling takes into account mean high tide and subsidence (4-6 feet). If we are at low tide when the tsunami arrive, the event will have a reduced impact, however, if we are at higher tides (King Tides, Higher Astronomical Tides), the event could have a greater impact.

For a large earthquake and tsunami event, such as this modeled event, there is the possibility of PREQUAKES, the main 9.0 Earthquake and hundreds of AFTERSHOCKS, some potentially capable of producing additional tsunami waves.

Your actions are exactly the same for any felt earthquake along the coast – MOVE TO HIGHER GROUND! The earthquake DOES NOT have to reach a magnitude 9.0 to produce a tsunami.

For more information about this new model, Please attend the TSUNAMI ROADSHOW, Wednesday April 11, 2018:

  • Begins at 12:00 p.m. at the Ocosta Junior-Senior High School Library, 2580 Montesano St, Westport
  • Begins at 6:00 p.m. at the Ocean Shores Convention Center, 120 W. Chance a La Mer, NW Ocean Shores
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