March 02, 2001
On February 28, 2001 at 10:54 am the Seattle / Olympia, Washington area was rocked by a magnitude 6.8 earthquake. The quake damage may exceed 1 billion dollars, and at least one person was killed. The region has a history of large earthquakes - most recently a magnitude 6.5 in 1965 and a 7.1 in 1949.
Washington is situated at a convergent continental margin, the collisional boundary between two tectonic plates. The Cascadia Subduction Zone, which is the convergent boundary between the North America plate and the Juan de Fuca plate, lies offshore from northern-most California to southern-most British Columbia. The two plates are converging at a rate of about 3-4 cm yr; in addition, the northward-moving Pacific plate is pushing the Juan de Fuca plate north, causing complex seismic strain to accumulate. Earthquakes are caused by the abrupt release of this slowly accumulated strain.
The image above is a snapshot of a 3 dimensional visualization of the earthquake region. The orange ball indicates the earthquake's hypocenter; the yellow dots are hypocenters of previous earthquakes from 1988-1995 with a magnitude greater than 3. The tick marks on the map's depth axis represent 10 km distances down into the earth; the depth axis has been exaggerated three times normal so the data can be more easily read. The great depth of the earthquake (over 50 km) made the surface damage less extensive than a shallower quake.