Saturday 10 November 2012

Earthquake off Vancouver Island.

On Wednesday 8 November 2012, slightly after 2.00 am local time (slightly after 6.00 pm on Thursday 7 November, GMT) the United States Geological Survey recorded a magnitude 6.3 Earthquake at a depth of 16.6 km, roughly 120 km off the southwest coast of Vancouver Island, British Columbia. This is a large quake and would potentially be very dangerous in an inhabited area, but it happened a long way off shore, and at an hour when most human beings were asleep, so there was no damage or casualties and only a few people on Vancouver Island felt the quake.

Map showing the location of the 8 November quake. Google Maps.

Vancouver Island is located on the western margin of the North American Plate, close to the Challenger Trench, along which the Explorer and Juan de Fuca Plate are being subducted. These are two remnant parts of the ancient Farallon Plate, which formerly underlay part of the eastern Pacific, and which has now been largely subducted beneath North America. The Explorer an Juan de Fuca Plates pass under the North American Plate as they sink into the Earth, but this is not a smooth process, with the plates constantly sticking together then breaking apart as the tectonic stresses build up.

Diagrammatic representation of the subduction of the Explorer and Juan de Fuca Plates beneath the North American Plate, close to Vancouver Island. Black Stars show major historic Earthquakes. Government of British Columbia.

Witness reports can help geologists to understand the processes going on in Earthquakes and the structures in the rocks that cause them. If you felt this quake you can report it to Natural Resources Canada here.

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