Vancouver Island Earthquake 1946
Canada's Largest Recorded Seismic Event on Land
Feb 12, 2009 Maureen K. Fleury
On Sunday, June 23rd, 1946 at 10:30 am, an earthquake with the magnitude of 7.3 struck Vancouver Island in British Columbia, Canada. The epicentre was located at Forbidden Plateau in central Vancouver Island.
The town of Courtenay, located east of the epicentre, was directly impacted by the earthquake. Tremors were felt as far north as Prince Rupert, British Columbia and as far south as Portland, Oregon.
Geology of Western British Columbia, Canada
Stretching from the Queen Charlotte Islands down to the northern tip of Vancouver Island, is the Queen Charlotte fault line. This is where the Pacific Plate is sliding northwest against the North America plate. There was an earthquake of 8.1 that occurred on this fault line on August 22, 1949.
In the ocean, west of Vancouver Island, there is a region known as the Cascadia subduction zone. This zone stretches from the northern tip of Vancouver Island down to northern California. The Juan de Fuca plate is subducting (sliding) under the North America plate.
It is believed that these two plates are currently locked together but it is squeezing the earth’s crust and causing numerous small earthquakes each year. At some point in time, it is anticipated that these two plates will break away from each other.
According to Natural Resources Canada, “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. Geological evidence also indicates that huge subduction earthquakes have struck every 300-800 years“.
Some of the areas affected by the 1946 Vancouver Island earthquake were not near the epicentre. With varied geological features, there are different reactions. Near a body of water, the soil is not strong due to containing clay and sand. This unsteady soil causes liquefaction and amplification. Coastlines and islands experienced damage even though they were not near Forbidden Plateau. In the Coastal Mountains, slopes are steep and not stable so there were several landslides during the 1946 earthquake.
Damaged Caused by the 1946 Vancouver Island Earthquake
In 1946, the population in the area was small and most of the buildings were constructed out of wood. There were very few bridges and dams built at the time. Most of the damage was done to chimneys that shook loose and crumbled. Over 75% of the chimneys in the area were affected.
In Courtenay, larger structures in the downtown area suffered damage. The chimney at the elementary school collapsed and fell through the roof. The school was empty because the earthquake struck on a Sunday.
Bricks fell off the rooftop fascia on the post office building. Some of the homes built on weaker foundations were shifted.
Neighbouring towns of Powell River, Port Alberni and Union Bay also suffered damage. Bricks fell from the bank building in Port Alberni. The pavement in some parts of the Island Highway shifted or broke loose.
Lighthouses along the waterways experienced shattered windows and seven-foot high tsunami rolled onto Texada Island in the Straights of Georgia.
Further away in Victoria and Vancouver, tall buildings swayed and shook but there was little or no damage.
There were only two deaths resulting from the 1946 Vancouver Island earthquake. One man died when his small boat capsized from waves generated by the earthquake. Another man from Seattle died from a heart attack.
Related Articles on Natural Disasters in British Columbia:
Comox House Failure 1946 Earthquake
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Chimney Damage, Port Alberni 1946 Earthquake
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Chimney Collapse, Courtenay 1946 Earthquake
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Damage to Bank, Port Alberni 1946 Earthquake
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Soiol Failure, Kelsey Bay Highway 1946 Earthquake
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