- Juan de Fuca Plate
The Juan de Fuca Plate, named after the explorer, is a
tectonic platearising from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plateat the Cascadia subduction zone. It is bounded on the south by the Blanco Fracture Zone, on the north by the Nootka Fault, and along the west by the Pacific Plate. The Juan de Fuca Plate was originally part of the once-vast Farallon Plate, now largely subducted under the North American Plate, and has since fractured into three pieces. The plate name is in some references applied to the entire plate east of the undersea spreading zone, and in other references only to the central piece. When so distinguished, the piece to the south is known as the Gorda Plateand the piece to the north is known as the Explorer Plate. The separate pieces are demarcated by the large offsets of the undersea spreading zone manifested in the above mentioned fracture zone and fault.
This subducting plate system has formed the
volcanic Cascade Range, the Cascade Volcanoesand the Pacific Ranges, which is part of the Pacific Ring of Fire, along the west coast of North Americafrom southern British Columbiato northern California.
The last major earthquake at the Cascadia subduction zone was the
1700 Cascadia earthquake, estimated to have a magnitude of 8.7 to 9.2. Based on carbon datingof local tsunamideposits, it occurred around 1700. As reported in " National Geographic" on December 8, 2003, Japanese tsunamirecords indicate the quake happened the evening of Tuesday, January 26, 1700.
In 2008 small earthquakes were observed within the plate. The unusual quakes were described as "more than 600 quakes over the past 10 days in a basin 150 miles southwest of Newport." The quakes were unlike most quakes in that they did not follow the pattern of a large quake, followed by smaller aftershocks; rather, they were simply a continual deluge of small quakes. Furthermore, they did not occur on the techtonic plate boundary, but rather in the middle of the plate. The subterranean quakes were heard on hydrophones, and scientists described the sounds as similar to thunder, and unlike anything heard previously. [* [http://www.sciencedaily.com/releases/2008/04/080413184801.htm Science Daily article about chain quakes detected from Juan de Fuca Plate, April 2008] ]
Geology of the Pacific Northwest
* [http://news.nationalgeographic.com/news/2003/12/1208_031208_tsunami.html National Geographic on Japanese records verifying an American earthquake]
* [http://www.washington.edu/burkemuseum/geo_history_wa/Cascade%20Episode.htm Cascadia tectonic history with map]
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