The 2001 Nisqually earthquake, having a moment magnitude of 6.8, with epicenter in the southern Puget Sound, damages Seattle metropolitan area.

The 2001 Nisqually earthquake occurred at 10:54:32 local time on February 28, 2001, and lasted nearly a minute. The intraslab earthquake had a moment magnitude of 6.8 and a maximum Mercalli intensity of VIII (Severe). The epicenter was in the southern Puget Sound, northeast of Olympia, but the shock was felt in Oregon, British Columbia, eastern Washington, and Idaho. This was the most recent of several large earthquakes that occurred in the Puget Sound region over a 52-year period and caused property damage valued at $1–4 billion. One person died of a heart attack and several hundred were injured.

The moment magnitude scale is a measure of an earthquake's magnitude based on its seismic moment. M_w  was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Similar to the local magnitude/Richter scale (M_L ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale.

The epicenter, epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates.

Puget Sound is a complex estuarine system of interconnected marine waterways and basins located on the northwest coast of the U.S. state of Washington. As a part of the Salish Sea, the sound has one major and two minor connections to the Strait of Juan de Fuca, which in turn connects to the open Pacific Ocean. The major connection is Admiralty Inlet; the minor connections are Deception Pass and the Swinomish Channel.