A Magnitude 5.5 Earthquake occurred off the southeast coast of Vancouver Island in British Columbia, slightly after 6.20 am local time (slightly after 1.20 pm GMT) on Sunday 4 August 2013, according to Natural Resources Canada. The quake was felt across much of the island, but there are no reports of any damage or casualties, and no tsunami warning has been issued.
The approximate location of the 4 August 2012 Vancouver Island Earthquake. 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.
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.
See also Magnitude 4.3 Earthquake in central Washington State, Earthquake off the coast of Alaska, Earthquake off Vancouver Island and Earthquake off the coast of Vancouver Island. 9 September 2011.
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