Editing Cascadia subduction zone (section)

==Geophysics==
[[Image:JuandeFucasubduction.jpg|thumb|upright=1.4|Structure of the Cascadia subduction zone]]

The Cascadia subduction zone is a {{convert|1000|km|abbr=on}} long dipping [[Fault (geology)|fault]] that stretches from Northern Vancouver Island to [[Cape Mendocino]] in northern California. It separates the Juan de Fuca and North America plates. New Juan de Fuca plate is created offshore along the [[Juan de Fuca Ridge]].<ref name="Juan de Fuca Volcanics">{{cite web|url=http://vulcan.wr.usgs.gov/Volcanoes/JuanDeFucaRidge/description_juan_de_fuca.html|title=Juan de Fuca Volcanics|access-date=2008-05-06}} USGS</ref><ref name="Roadside Geology of Oregon">{{cite book|title=Roadside Geology of Oregon|year=1978|publisher=Mountain Press|first1=David D.|last1=Alt|first2=Donald W.|last2=Hyndman|location=Missoula, Montana|isbn=978-0-87842-063-6|edition=19th|page=3}}</ref>

The Juan de Fuca plate moves toward, and eventually is pushed under the continent (North American plate). The zone separates the [[Juan de Fuca plate]], [[Explorer plate]], [[Gorda plate]], and [[North American plate]]. Here, the [[oceanic crust]] of the Pacific Ocean has been sinking beneath the continent for about 200&nbsp;million years, and currently does so at a rate of approximately 40&nbsp;mm/[[year|yr]].<ref name="Juan de Fuca Volcanics"/><ref name="Roadside Geology of Oregon"/>

At depths shallower than {{convert|30|km|abbr=on}} or so, the Cascadia zone is locked by friction while stress slowly builds up as the subduction forces act, until the fault's frictional strength is exceeded and the rocks slip past each other along the fault in a [[megathrust earthquake]]. Below {{convert|30|km|abbr=on}} the plate interface exhibits [[episodic tremor and slip]].

The width of the Cascadia subduction zone varies along its length, depending on the angle of the subducted oceanic plate, which heats up as it is pushed deeper beneath the continent. As the edge of the plate sinks and becomes hotter and more molten, the subducting rock eventually loses the ability to store mechanical stress; [[earthquake]]s may result. On the Hyndman and Wang diagram (not shown, click on reference link below) the "locked" zone is storing up energy for an earthquake, and the "transition" zone, although somewhat plastic, could probably rupture.<ref>{{Cite web|url=https://www.researchgate.net/publication/247990703|title=The rupture zone of Cascadia great earthquakes from current deformation and thermal regime|website=ResearchGate}}</ref>

The Cascadia subduction zone runs from [[triple junction]]s at its north and south ends.  To the north, just below [[Haida Gwaii]], it intersects the [[Queen Charlotte Fault]] and the [[Explorer Ridge]].  To the south, just off Cape Mendocino in California, it intersects the [[San Andreas Fault]] and the [[Mendocino fracture zone]] at the [[Mendocino triple junction]].{{clear}}