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Three strong, shallow quakes but no tsunami off B.C. coast

Last Updated Oct 22, 2018 at 11:50 am PDT

(iStock Photo)
Summary

Three strong, shallow earthquakes hit off the coast of B.C. Sunday night, but did not trigger tsunamis

The three earthquakes that struck off B.C.'s coast Sunday all hit within an hour

VANCOUVER (NEWS 1130) –┬áIf you needed a reminder we live right beside one of the most seismically active areas in Canada, it came Sunday night.

Three strong, shallow earthquakes hit off the B.C. coast a little after 10:30 p.m., and one seismologist says they were unusual.

“They were located about 200 kilometres west of Vancouver Island between magnitude 6.5 and 6.8, so very large earthquakes,” says John Cassidy with the Geological Survey of Canada, adding that they were at a relatively shallow depth of 10 kilometres below the ocean floor.

It is the timing of the quakes that has Cassidy taking notice, with all three striking within an hour.

“Large earthquakes occur in that area every few years, and about every decade we see them in the magnitude 6.0 to 6.5 range,” he tells NEWS 1130. “What we haven’t seen before is three large earthquakes like this — it’s uncommon to see that within a very short window of time, like an hour. That’s a little bit different.”

So is it a sign of anything? Cassidy asserts that the tight timing is not indicative of anything more powerful to come.

“It doesn’t tell us when a bigger earthquake might occur or if an earthquake will happen closer to land. It doesn’t tell us anything about what we can expect in the future other than we know there will be aftershocks over the coming hours and coming days.”

The shaking could be felt on parts of Vancouver Island, but there have been no reports of any damage or injuries and Cassidy says no tsunami warnings were issued.

“The earthquakes occurred on what we call a transformed fault, and the type of movement we are looking at here is sort of a sideways slipping, so its not generally the type of earthquake that you would see generating large tsunamis,” he explains. “That would typically involve a vertical movement of the sea floor.”

But Cassidy says it is a good reminder that the province’s south coast is a very active earthquake zone.

“These earthquakes resulted from the movement of tectonic plates off the coast of British Columbia. The plates are moving at about the same speed that your fingernails grow, between three to five centimetres per year. Earthquakes happen every day, including large earthquakes on occasion. Being aware and being prepared is really important.”

Early warning system tested with three earthquakes

The three strong earthquakes were picked up by B.C.’s offshore early warning system.

Oceans Network Canada says preliminary results look good.

“As you can imagine, we’re still building out that system so more sensors, more upgrades to software, et cetera,” Teron Moore with the organization explains. “So an event like this really helps us to test and refine, and so far it looks really good.”

Their array on the ocean floor picked up a lot of data and sent it through their system to figure out if an alert was needed for earthquake early-warning end users.

 

The system is still being tested and refined, but it can be used to alert first responders and medical facilities, even used for automated actions like shutting down gas lines and rapid transit before shaking starts.

“If an earthquake happens and that hall is shaken, the doors of the firehall might be jammed. So simply just opening the firehall doors before the shaking hits will really allow first responders to do their jobs.