Geological Origins
The Puget Sound area, where this earthquake occurred, is prone to deep earthquakes due to the Juan de Fuca tectonic plate's subduction under the North American Plate at 3.5 to 4.5 cm. a year as part of the Cascadia subduction zone, which causes stress in the former as it sinks into the mantle. As an intraslab earthquake, it was produced by a change in volume as rock changed from one form to another. Similar significant earthquakes occurred in the same general region on April 29, 1965 (magnitude 6.5, depth 63 km (39 mi)), and April 13, 1949 (magnitude 7.1, depth 53 km (33 mi)).
Read more about this topic: 2001 Nisqually Earthquake
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