1946 Vancouver Island earthquake

The 1946 Vancouver Island earthquake was a 7.3 magnitude earthquake that struck Vancouver Island on the coast of British Columbia, Canada at 10:15 a.m. on Sunday, June 23, 1946.² 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.³ Shaking was felt from Portland, Oregon to Prince Rupert, British Columbia. The earthquake is remembered as one of the most damaging earthquakes in the history of British Columbia. However, damage was restricted because there were no heavily populated areas near the epicenter, where the violent shaking occurred.

Geography

The tectonics that caused the 1946 Vancouver Island earthquake are poorly known. No surface expression of the offset was noticed, most likely because the epicenter area is very remote and greatly forested. A comprehensive examination and computer interpretation of seismic data from over 50 stations has shown that the possible explanation of the earthquake includes a strike-slip fault corresponding to the lengthy axis of Vancouver Island known as the Beaufort Range Fault.⁵ 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 this is a lower likelihood in this case because the earthquake should have given 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 the Courtenay and Campbell rivers. 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 epicenter was positioned somewhere in the Forbidden Plateau region, located in central Vancouver Island.

Damage and casualties

The earthquake only caused two casualties, however, it was still a very destructive earthquake. These two resulted from one of the two, both men, having a heart attack, while the alternate man drowned when the dinghy he was located on was consumed by a wave. Of the two men, both were over the age of 49; their names were Jacob L. Kingston, 69, and Daniel Fidler, who was 50.¹

In Vancouver, damage consisted of lofty buildings oscillating violently and a piece of masonry fell off of the local railway station. In addition, within the city at least one gas line cracked and several power outages occurred. Fires broke out in several chimneys and at least one swing span bridge was fractured by the shaking. In the Hotel Vancouver, a senior building, more than 500 war veterans' families fled the flames. One writer, George Finley, stated that the Lions' Gate Bridge "swayed like a leaf", coinciding a "low, rumbling sound, like a deep growl."¹

The 1946 Vancouver Island earthquake demolished 75% of chimneys in the communities of Cumberland, Union Bay, and Courtenay and caused extensive damage in Comox, Port Alberni, and Powell River on the eastern side of Strait of Georgia.² Some chimneys were fractured in Victoria and people in Victoria and Vancouver were terrified, including people running into streets.²

Landslides created by the earthquake were frequent throughout Vancouver Island.⁶ Extensive rates of sinking was involed with this earthquake, most commonly around shorelines of the Strait of Georgia.⁶ This included the bottom of Deep Bay which sank between 2.7 m (9 ft) and 25.6 m (84 ft).⁷ These measurements were reported by the Canadian Hydrographic Department.⁷ Also, a 3 m (10 ft) ground shift occurred on Read Island.⁷ Ships throughout the region suffered trembling and the people that were on the ships during the earthquake defined it as either having run over a sand bar or striking a rock.⁶ Submarine power lines were destroyed in the long narrow Alberni Inlet and near the city of Powell River.⁶ All lighthouse keepers in the adjacent area felt the earthquake and experienced a little amount of destruction, including fractured windows and smashed dishes.⁶ A tsunami struck the west coast of Texada Island with two waves, the first was 2 m (7 ft) high and the seconed 1 m (3 ft) high.⁶ One fortunate occurrence allowed researchers afterward to review the effects of the earthquake: an aerial photographic survey had been established of Vancouver Island in 1946, after the earthquake, and these were studied by a geoscientist in the late 1970s.⁶

South of the Canada – United States border in Washington State, some chimneys fell at Eastsound and on Orcas Island and a concrete mill was damaged at Port Angeles.⁷ In Seattle, some damage occurred on upper floors of tall buildings and one bridge was damaged, but traffic was not slowed down. The shock was strongly felt at Bellingham, Olympia, Raymond, and Tacoma.⁷ It was powerful enough to knock the needle off a seismograph at the University of Washington, and was sustained for about a minute even in Seattle. The earthquake caused somewhat astounding movement among structures, moving one 300 ft (91 m) wall about 35 ft (11 m) and caused one home to shift for 5 ft (2 m) off its foundation.¹ The total affected area in Canada and the United States was about 260,000 km² (100,000 sq mi).⁷

Contents

Geography

Damage and casualties

See also

References