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Megathrust Earthquake Although megathrust earthquakes have not been recorded in British Columbia, past earthquakes have left a geological record of this occurrence. After the earthquake, the strain accumulated is released and vertical deformation results in the over-riding plate that is the reverse of that seen during stress build up. Thus areas like Vancouver Island, that have risen slightly before the quake, suddenly subside.
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Most recorded earthquakes are caused by stress
accumulation within the plates. In BC and offshore
earthquakes have occurred either within the Juan de Fuca or
the North American plates. None have occurred along the
junction where the two plates are actually in contact.
The apparent inactivity within the zone of contact
between the plates suggests that either the plates are
locked together and are accumulating strain or that the
contact zone is well lubricated and the plates are moving
smoothly past each other. This stress accumulation can
result in a potentially very destructive type of
earthquake, called a megathrust earthquake.
