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.
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.
this animation the Juan de Fuca plate (dark brown
is sliding under the North American Plate (light
brown). The red bar indicates that the plates
become locked and the edge of the NA plate begins
to slowly rise and buckle. over a period for
200-300 years the energy built up causes the
locked portion to give way and the upper plate
snaps back into its original position. The vertical displacement scale has been
exaggerated for the purpose of the animation.