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UW Emergency Management

Washington earthquakes

QuakesKnown as the triple threat!

Crustal or shallow quakes

Occur in the North American plate at 0-30 km near the crust’s surface along faults. Intense shaking occurs near the epicenter but usually diminishes quickly with distance relative to the other earthquake types. Shallow quakes are the type expected on the Seattle Fault zone, which is the primary but not only source for shallow quakes in Seattle.

Deep or intraplate quakes

Occur at depths of 30-70 km in oceanic crust as it dives under lighter continental crust. Because of the depth, even buildings located right above them are far enough away that ground motions are attenuated. Deep quakes are the most common large earthquakes that occur in the Puget Sound region. Quakes larger than 6.0M occurred in 1909, 1939, 1946, 1949, 1965 and 2001.

Subduction zone or megathrust quakes

Occur on the interface between the North American plate and the San Juan de Fuca plate, a small plate extending from northern California to British Columbia. These are the largest type of earthquakes in the world.

Other videos about earthquake hazards in Seattle