Each year, seismologists with the Geological Survey of Canada record and locate more than 1000 earthquakes in western Canada. The earth’s crust is made up of plates that can either slide past one another, collide, or diverge (move apart). The west coast of Canada is one of the few areas in the world where all three of these types of plate movements take place, resulting in significant earthquake activity.
Canada’s largest earthquake in recent times (magnitude 8.1) occurred on August 22, 1949 off the coast of BC. It occurred on the Queen Charlotte Fault – the boundary between the Pacific and North American plates that runs underwater along the west coast of the Haida Gwaii (formerly Queen Charlotte Islands) off the west coast of British Columbia.
The shaking was so severe on the Haida Gwaii that cows were knocked off their feet, and a geologist with the Geological Survey of Canada working on the north end of Graham Island could not stand up.
From northern Vancouver Island, to the Queen Charlotte Islands, the oceanic Pacific plate is sliding to the northwest at about 6 cm/year relative to North America. The boundary between these two giant plates is the Queen Charlotte fault – Canada’s equivalent of the San Andreas fault. Canada’s largest historical earthquake – a magnitude 8.1, occurred along this fault on August 22, 1949. This earthquake, larger than the 1906 San Francisco earthquake, caused nearly a 500-km-long segment of the Queen Charlotte fault to break.
Cascadia Subduction Zone:
West of Vancouver Island, and extending from the north tip of the Island to northern California, the oceanic Juan de Fuca plate is moving towards North America at about 2-5 cm/year. This region is called the Cascadia subduction zone.
Here, the much smaller Juan de Fuca plate is sliding (subducting) beneath the continent (it is about 45 km beneath Victoria, and about 70 km beneath Vancouver). The ocean plate is not always moving though.
There is good evidence that the Juan de Fuca and North America plates are currently locked together, causing strain to build up in the earth’s crust.
It is this squeezing of the crust that causes the 1000 or so small earthquakes that are located in southwestern British Columbia each year, and the less-frequent (once per decade, on average, damaging crustal earthquakes (e.g., a magnitude 7.3 earthquake on central Vancouver Island in 1946).
At some time in the future, these plates will snap loose, generating a huge offshore “subduction” earthquake – one similar to the 1964 M=9.2 Alaska earthquake, or the 1960 M=9.5 Chile earthquake. Current crustal deformation measurements in this area provide evidence for this model. Geological evidence also indicates that huge subduction earthquakes have struck this coast every 300-800 years.
Earthquakes in Canada for the past 30 days