Coastal communities got a gentle reminder over Christmas that they are living in the most earthquake-prone part of the country. Nine earthquakes struck in three days in the waters off northern Vancouver Island, including a magnitude 6.2 quake about 200 kilometres west of Port Hardy on Christmas Eve. No tsunami alert was issued and no damage was reported.
Earthquakes off the west coast of Vancouver Island are not uncommon, but since the island itself acts as a giant natural breakwater, the risk of a major tsunami rolling in from the open Pacific and hitting population centres on the Salish Sea seems remote.
But complacency would be a mistake. An article last summer in the Seismological Society of America’s journal GeoScienceWorld documented a major fault line that runs under the Strait of Georgia near Sechelt at an incredible depth of 65 kilometres.
Working from 30 years of data on seismic activity southwest of Texada Island, researchers identified an “earthquake nest” spanning up to 20 kilometres of the Juan de Fuca tectonic plate. The nest sits beneath the North America plate, and the four to 10 seismic events that occur each year lose most of their energy by the time they reach the surface. But a major rupture could trigger “the equivalent of a greater than 6.0 magnitude earthquake,” says article co-author Reid Merrill, a PhD student at UBC’s Department of Earth, Ocean and Atmospheric Sciences.
Merrill compares the potential impact to the 2001 Nisqually earthquake near Olympia, Wash., which injured hundreds of people and cost at least $1 billion in damage across greater Seattle. “The epicentre would be much closer to these metropolitan areas like Nanaimo and Vancouver and Sechelt,” he told CBC News in September. “In some ways these earthquakes … can be more dangerous than the megathrust or the Big One.”
His advice for municipal planners is to keep the threat in mind when evaluating new building sites. We would add that the risks associated with existing development should also be reviewed under the lens of these new findings.
As the saying goes: hope for the best and prepare for the worst.
