B.C. rattled by offshore quake
QUEEN CHARLOTTE, B.C.—After a sleepless night of tsunami warnings and aftershocks, triggered by a massive earthquake off British Columbia’s northwestern coast, Faye Beaulieu felt a small rumble inside her home around noon yesterday in the Haida Gwaii community of Queen Charlotte.
It was yet another aftershock—this time a magnitude-6.4, the most significant since the magnitude-7.7 quake the night before that itself was one of the biggest in Canadian history.
“It was only three or four seconds, just long enough to rattle everything—including me.”
The main quake struck Saturday a few minutes after 8 p.m., with an epicentre about 30 km off the coast of Haida Gwaii, formerly the Queen Charlotte Islands.
It triggered tsunami warnings along the B.C. coast and as far away as Hawaii.
There were reports of people feeling the quake throughout B.C., though there appeared to be no injuries or significant damage in the immediate area beyond broken picture frames and dishes.
The largest wave associated with the quake hit Langara Island, a northern Haida Gwaii island, and measured just 69 cm.
Beaulieu, who is the unit chief for the community’s ambulance service, was at home with her husband watching a movie and initially thought the rattling was coming from her home entertainment system.
But when she shut the movie off, the rattling didn’t stop.
“I really thought my house was coming down,” said Beaulieu, who said the shaking lasted about a minute.
“For how much the house was shaking, I’m surprised at how little happened,” she added.
The area is a hot spot for quake activity, with a major fault line just off the coast of the islands that make up Haida Gwaii.
It’s the same area that saw Canada’s largest earthquake ever recorded—a magnitude-8.1 quake back in 1949.
Saturday’s earthquake was Canada’s largest since that 1949 quake, noted John Cassidy, a seismologist with Natural Resources Canada.
“This was a huge earthquake—a magnitude 7.7 is the type of earthquake that only happens maybe one or twice around the world each year,” he added in an interview yesterday.
“It’s Canada’s equivalent to the San Andreas Fault.”
The quake happened as two tectonic plates—the Pacific plate and the North American Plate—slid past each other.
Cassidy said such horizontal movement typically doesn’t pose the same tsunami risks as vertical movement, which is the sort of quake that triggered the devastating 2010 tsunami in Japan.
The quake invariably prompted speculation about the “big one”—the type of earthquake that is believed to strike off the West Coast every 500 years or so and would create a massive tsunami and cause significant damage in British Columbia and the northwestern United States.
The last one was in 1700.
Brent Ward, an earth scientist at Simon Fraser University, said the big one would happen along a different fault than the one involved in Saturday’s quake, on the edge of the Juan de Fuca Plate west of Vancouver Island.
That plate is moving underneath the North American Plate, noted Ward, in a process known as subduction.
When it finally gives way, the results would be catastrophic.
“We would get the entire west coast of Vancouver Island being affected by a large tsunami, similar in size to the one that hit Japan,” he said.
“We would get intense ground shaking throughout southwestern B.C. down into Washington and possibly into Oregon, so we would see a very huge area affected by damaged buildings, damaged roads, and bridges.
“There would be fatalities,” he added.
But Ward cautioned against focusing too much on the big one. He said smaller—but still destructive—quakes are likely to be more frequent, pointing to a magnitude-7.3 quake that struck underneath Vancouver Island, near the community of Courtenay, in 1946.
“Everyone’s concerned about the big one, but the ones that are similar to what happened under Courtenay, these happen every 40 or 50 years,” noted Ward.
“If you compare similar-sized earthquakes and the damage they do, it would be a very significant event,” he warned.