British Columbia

Earthquake possible along new fault zone near Victoria say scientists

A newly-discovered fault will give B.C. south coast residents one more thing to worry about when prepping for earthquakes, say scientists.

It's a 125km-long series of faults that run from Washington to Victoria

The Devil's Mountain Faults, indicated here by a red line, is actually made up of a series of faults that run from Washington to Victoria. (Natural Resources Canada)

Seismologists in B.C. have confirmed the existence of a fault only five kilometres south of Victoria, giving South Coast residents one more thing to worry about when preparing for earthquakes.

It's called the Devil's Mountain Fault Zone and it's actually made up of a series of faults that run from Washington state to Victoria, running much closer to the B.C. capital than the point where the Juan de Fuca plate meets the North American plate, which scientists have predicted for decades will result in the 'Big One.'

Seismologists from Natural Resources Canada worked with the US Geological Survey to map the complex fault system on the ocean floor.

The findings were published in the summer of 2015 in the Geological Survey of Canada.

"This fault is about 125 km long from Washington to Victoria, which would be an earthquake, potentially, in the magnitude of 6.5, 7 perhaps even 7.5 if the entire fault zone ruptured at once," said John Cassidy, head of Earthquake Seismology at Natural Resources Canada.

Unlike the so-called 'Big One,' which will originate from the fault zone where the North American and Juan de Fuca plates meet, the Devil's Mountain Faults lie entirely on the North American plate, which usually generates smaller, shallower, crustal earthquakes.

The Juan de Fuca plate is moving toward and riding under the North America plate along a fault line west of Vancouver Island. (CBC)

Proximity matters

And the Devil's Mountain Faults probably won't rupture all at once, said Cassidy.

"There's no evidence that this fault has ruptured in that fashion all at once because it's a series of fault zones."

However, Cassidy says the proximity of the fault zone to a major urban centre — Victoria — could be an issue.

"The distance makes a huge difference … the shaking that can be just as strong from a much smaller earthquake that is only five to ten kilometres away from the city."

Next steps

Researchers are working to find out how often earthquakes occur at the Devil's Mountain Faults. The more frequently they happen, the more dangerous it is for residents living in the area.

"That's ongoing research to try and determine how often the fault moves, if it moves," said Cassidy.

In addition, governments will need to continue retrofitting old buildings and updating building codes according to new seismic information, said Cassidy.

"We're incorporating all of this new information into our earthquake hazard model and into building codes."

But overall the change will be small because the area is already on high alert in preparation for the next big earthquake, he said.

"It's not going to make a huge change because we already have a very high hazard level."

To listen to the full interview, click the link labelled: Devil's Mountain Faults Zone only 5km away from Victoria scientists confirm.