Why have there been so many earthquakes off the coast of B.C.?

There has been an increase of earthquake activity off the coast of British Columbia over the past month. Courtesy Natural Resources Canada

Over the past month there have been 169 earthquakes of magnitude 2.5 or above off the coast of British Columbia. Is this a sign of the “big one?”

“There has been a slight increase in activity,” said Alison Bird, seismologist with Natural Resources Canada. “But from time to time we have swarm activity off the coast.”

In fact, the last time it was so active was September 2013.

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“It’s pretty routine. With the kinds of tectonics in this region, the forces that the plates are under, it’s not a surprise that we have a sudden burst of small earthquakes.”

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There are many faults in that area west of Port Hardy. You have plates moving away from each other, others that are moving side by side, and then one plate that is sliding under another. All those different motions make it a hotbed of activity.

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Scroll over the interactive map for information on the earthquakes

Bird said that it’s unlikely that this swarm is associated with anything larger. That’s because it’s not in the right area, and that swarms don’t necessarily indicate something larger.

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Still, though it happens from time to time, that doesn’t mean that B.C. residents shouldn’t always be prepared.

“We will have the big one, the mega-thrust earthquake, other large earthquakes in this region, guaranteed. I just can’t tell you when they’re going to occur.”

Paul Caruso, a geophysicist with the U.S. Geological Survey, concurred.

“No one knows for sure,” he said. “We do get these swarms from time to time but that’s because it’s a very active area.”

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For the mega-thrust earthquake — the one we tend to call “The Big One” which would be somewhere near magnitude 9 — Bird says there is a one-in-ten chance of that happening within the next 50 years.

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But if people are prepared for that one, they will be prepared for anything.

When it comes to the Victoria area, there is a one in three chance of of magnitude 6 or bigger in the next 50 years.

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The magnitude 4.6 earthquake in Tofino is separate from the swarm occurring off the coast, but earthquakes occur in that region almost every day, Bird said. It’s just that that one was a little larger than most.

B.C. residents aren’t strangers to the shaking and rattling of the earth. But it’s possible that, because a large earthquake hasn’t occurred in a long time, people forget that one day they could face a much more dangerous situation.

“They’re a good reminder that this is earthquake country. We really have to respect that,” Bird said. “The thing is, we haven’t had anything truly large for so long that people have become complacent and don’t grasp the threat in the region.”

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Bird has some advice.

“Just be prepared regardless of what’s happening with the earthquakes.”

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