1946 Vancouver Island earthquake
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| Date | June 23, 1946 |
|---|---|
| Magnitude | 7.5 Mw |
| Depth | ~ 20 km (12 mi) |
| Epicenter | 49°45′N 124°30′W / 49.75°N 124.5°W |
| Areas affected |
Canada United States |
| Total damage | Limited |
| Max. intensity | VIII (Severe) |
| Casualties | 2 killed |
The 1946 Vancouver Island earthquake occurred with a moment magnitude of 7.5 that struck Vancouver Island, on the Coast of British Columbia, Canada, at 10:15 a.m. on June 23. The main shock epicenter occurred in the Forbidden Plateau area northwest of Courtenay. While most of the large earthquakes in the Vancouver area occur at tectonic plate boundaries, the 1946 Vancouver Island earthquake was a crustal event. Shaking was felt from Portland, Oregon to Prince Rupert, British Columbia. This is one of the most damaging earthquakes in the history of British Columbia, but damage was restricted because there were no heavily populated areas near the epicentre, where severe shaking occurred.
This earthquake is Canada's largest historic onshore earthquake. However, the greatest earthquake in Canadian history recorded by seismometers was the 1949 Queen Charlotte earthquake, an interplate earthquake that occurred on the ocean bottom just off the rugged coast of Graham Island, which reached magnitude 8.1 on the moment magnitude scale.
The tectonics that caused the 1946 Vancouver Island earthquake are poorly known. No surface expression of the offset was noticed, most likely because the epicentre area is very remote and densely forested. A comprehensive examination and computer interpretation of seismic data from over 50 stations has shown that a possible explanation of the earthquake includes a strike-slip fault corresponding to the lengthy axis of Vancouver Island, known as the Beaufort Range Fault. A fault running across Vancouver Island, corresponding to the projection of the underwater Nootka Fault on the British Columbia Coast, is also a possibility but an unlikely one because the earthquake showed no evidence of offsets along a series of highways that follows much of the eastern coastline of Vancouver Island, called Island Highway, and other roads between Courtenay and Campbell River. The estimated depth of the earthquake places it within the continental crust, not at the margin with the Cascadia subduction zone, and certainly not inside the subduction zone itself. Specifically, the earthquake's epicentre was positioned somewhere in the Forbidden Plateau region, in central Vancouver Island.
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