Napa earthquake a reminder of risks in Washington state; New map shows risk levels

Earthquake damage risk
Relative risk for earthquake damage in Washington and Oregon shown in red, orange and yellow. Image: USGS.

A few weeks before Sunday’s 6.0 magnitude earthquake in northern California, the U.S. Geological Survey (USGS) released an updated earthquake risk map for the lower 48 states. The maps, used for building codes and insurance purposes, calculate how much shaking a building might experience during its lifetime from the biggest earthquake likely in the area. As the maps show, Washington state — from the Cascade Mountains to the Pacific Ocean — is at high risk from damaging earthquakes. In fact, we face a triple threat:

  • Shallow or crustal earthquakes, such as those that can be caused by the Seattle Fault
  • Deep intraslab earthquakes, such as the 6.8 magnitude Nisqually earthquake of 2001
  • Mega-thrust earthquakes, such as the 9.0 magnitude Cascadia earthquake of 1700

A magnitude 9.0 earthquake on the Cascadia subduction, which lies just off the coasts of Washington, Oregon, northern California, and British Columbia, would be one thousand times more powerful than the Nisqually earthquake of 2001. The impacts on coastal communities could be similar to the effects of earthquakes that struck Japan in March 2011 and Chile in February 2010.

Emergency managers and preparedness experts agree that “Drop, Cover, and Hold On” can help reduce injuries and deaths during earthquakes.

  • DROP to the ground (before the earthquake drops you!),
  • Take COVER by getting under a sturdy desk or table, and
  • HOLD ON to your shelter and be prepared to move with it until the shaking stops.

You cannot tell from the initial shaking if an earthquake will suddenly become intense… so always Drop, Cover, and Hold On immediately.

Find information about preparing for — and surviving — an earthquake on the Washington State Emergency Management Division website.

Visit the Washington State Seismic Hazards Catalog to see interactive graphic representations of how a major earthquake might affect your area of the state.

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