British Columbia hosts Canada's most rapidly developing coastal communities along the semi-enclosed waterways of the Strait of Georgia. This region also is Canada's most seismically active zone. In 1946, the Vancouver Island M7.3 earthquake caused a number of submarine failures of sand and gravel shoreline deposits, destroying coastal facilities, shearing submarine cables and causing large, destructive waves. Multibeam and sidescan sonar technologies have been used to map three submarine landslides at Goose Spit, Mapleguard Spit and Grief Point. These sites are 32–55 km from the epicentre. The data image the failures in great detail, providing important information on size and style of mass-wasting. The total combined area affected by these three failures is over 1.3 × 10⁶ m². Submarine cores show the spit failures consisted of well-rounded beach gravel, cobble and sand, in some cases suspended in a cohesive mud matrix, while the Grief Point failure was likely a debris flow avalanche. Cone penetration tests at Goose Spit show soil profiles prone to liquefaction, lateral spreading and post-liquefaction landsliding with reasonably low ground accelerations.