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A map of the Juan de Fuca Plate

Cutaway of the Juan de Fuca Plate. USGS image

The Juan de Fuca Plate, named after the explorer, is a tectonic plate arising from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate at 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 Plate and 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 Volcanoes, and the Pacific Ranges, which is part of the Pacific Ring of Fire, along the west coast of North America from southern British Columbia to northern California.

The last major earthquake at the Cascadia subduction zone was the 1700 Cascadia earthquake, estimated to have a moment magnitude of 8.7 to 9.2. Based on carbon dating of local tsunami deposits, it occurred around 1700. As reported in National Geographic on 8 December 2003, Japanese tsunami records indicate the quake happened the evening of Tuesday, 26 January 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 tectonic 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.^[1]

See also

• Geology of the Pacific Northwest

References

External links

• National Geographic on Japanese records verifying an American earthquake
• Cascadia tectonic history with map

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