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Seattle Fault

Seattle Fault · King County · last large earthquake close to A.D. 900

A roughly 70-kilometer thrust under Seattle can host a magnitude 7 to 7.5 earthquake. USGS says the last large one was close to the year 900.

The Seattle fault is a north-directed thrust that runs under the city. USGS describes a zone about 70 kilometers long. The agency says the fault can host a magnitude 7 to 7.5 earthquake. High-resolution marine seismic imaging has mapped the zone under Puget Sound.

The most recent large earthquake on the Seattle fault occurred close to the year 900. Other USGS work dates that event to about A.D. 900–930 from uplifted shorelines and tsunami deposits. That is the last large rupture USGS cites for the fault.

The Seattle Field Office places the fault among the crustal sources that can shake the Puget Lowland hard, separate from the deeper Cascadia megathrust. The sources below are the public USGS record of the fault and the marine seismic study.

Geography & Geology
Science / Strange Washington

Sources (2)

government · Tier S
U.S. Geological Survey
Seattle Field Office
government · Tier S
U.S. Geological Survey
High-resolution marine seismic imaging of the Seattle fault zone

Last reviewed: September 20, 2026

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