6.4M quake that struck off B.C. is part of recent 'swarm': agency

A series of four earthquakes, including one with a preliminary magnitude of 6.4, struck off the coast of Vancouver Island on Thursday morning, part of an ongoing "swarm" of quakes being detected off the British Columbia coast.

The first and largest quake occurred at 8:08 a.m. PT at a depth of 10 kilometres, 183 kilometres southwest of Port Alice, B.C., according to Earthquakes Canada.

The agency said no tsunami and no damage was expected, but the earthquake might have been felt by some residents of Vancouver Island.

The 6.4-magnitude quake was followed by one preliminarily measured at 4.3 magnitude at 8:35 a.m. PT, another at 4.9 magnitude at 9:17 a.m. PT, and yet another preliminarily measured at 4.8 magnitude at 10:34 a.m. PT, all near the same location.

A total of 13 earthquakes with a preliminary magnitude of around 4.0 or greater have now been detected in B.C. waters since the start of July.

A notice posted to the Earthquakes Canada website says the agency is tracking a "swarm of earthquakes offshore Vancouver Island, at the intersection of the northern Juan de Fuca Ridge, Sovanco Fracture Zone and Nootka Fault Zone."

Natural Resources Canada seismologist John Cassidy described the region as a "really complicated tectonic setting," in an interview with CBC News in Victoria after the earthquakes hit.

"We have plates moving apart, sliding past one another and we have, in fact, three major fault systems that intersect in the vicinity of these earthquakes," he said. "Going back as long as we've been recording earthquakes, it's one of the most active zones in Canada."

He said while there is no reason to be concerned about the current cluster of quakes posing a risk to safety given their depth and distance from land, they do serve as a reminder that B.C.'s coast is susceptible if and when an earthquake strikes closer to the shore.

"This sequence doesn't tell us when a large earthquake will happen closer to land, but it does remind us that we live in a very active zone," Cassidy said.

The current quakes also give scientists useful data to help better predict and understand future rumblings, he added.

"This earthquake ... will be very useful for us in terms of understanding what we can expect from future events," he said.