An earthquake is the sudden release of stored energy. Most earthquakes occur along a fracture within the earth, called a fault. The shaking caused by this sudden shift is often very small, but occasionally large earthquakes produce very strong ground shaking. It is this strong shaking and its consequences – ground failure, landslides, liquefaction – that damages buildings and structures and upsets the regional economy.
Washington, especially the Puget Sound basin, has a history of frequent earthquakes. More than 1,000 earthquakes occur in the state each year. A dozen or more are strong enough that people feel ground shaking. Occasionally, earthquakes cause damage. The state experienced at least 20 damaging events in the last 125 years.
The Nisqually earthquake on February 28, 2001, was a deep, magnitude 6.8 earthquake 10 miles northeast of Olympia. One person died of a heart attack, hundreds were injured, and various estimates place damage at between $500 million and $4 billion. Exact figures are not available, as insurance claims information is not available.
The earthquake threat in Washington is not uniform.
On July 2, 1999, there was a 5.8 earthquake centered in the Satsop area of Grays Harbor County -- although the earthquake was felt a few counties over, most other areas didn't see damage. In Grays Harbor, the damage was estimated at $8.1 million, including repairing and retrofitting its historic courthouse in Montesano.
While most earthquakes occur in Western Washington, some damaging events, such as the 1872 magnitude 6.8 (est.) quake, do occur east of the Cascades. Geologic evidence documents prehistoric magnitude 8 to 9.5 earthquakes along the outer coast, and events of magnitude 7 or greater along shallow crustal faults in the urban areas of Puget Sound.
The Cascadia subduction zone, the fault boundary between the North America plate and the Juan de Fuca plate, lies offshore from northern California to southern British Columbia. The two plates are converging at a rate of about 2 inches per year. In addition, the northward-moving Pacific plate is pushing the Juan de Fuca plate north, causing complex seismic strain to accumulate. The abrupt release of this slowly accumulated strain causes earthquakes.
Seismic Safety in Washington
The Geology Division of the Washington State Department of Natural Resources (DNR) conducts geologic hazards mapping across the state and works to identify our earthquake threats. In addition, the United States Geological Survey works closely with DNR to provide the most accurate, credible, and up-to-date scientific earthquake information to the public and emergency management community. Their work forms the basis for the implementation of seismic provisions and standards in building codes and other infrastructure protection standards. For additional information about the earthquake hazards in Washington, see the links below:
- Earthquakes in Washington (DNR)
- Geological Mapping of Washington (DNR)
- Washington Earthquake Information (USGS)
- Earthquake Hazards Program (USGS)
- Seismology and Tectonics (UW)
- Slides from Catastrophic Disaster Planning Workshop (PDF)
- Earthquake and Tsunami School Resource Guide (PDF)
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- For Kids:
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