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Haida Gwaii’s weekend of tremors sheds new light on future disasters

The epicentre of Saturday's 7.7 magnitude earthquake.

U.S. Geological Survey

Dozens of aftershocks rattled B.C.'s north coast on Sunday, underscoring the force of a 7.7-magnitude earthquake that hit the region on Saturday.

And while not exactly a surprise – the quake took place in an earthquake zone that was hit by an 8.1-magnitude tremor in 1949 – the recent jolt is expected to shed new light on when and where future disasters could occur.

"There's a lot of new data that will be available from this earthquake that will allow us to map out exactly how the fault moved during this earthquake and where the fault slipped," Natural Resources Canada seismologist John Cassidy said on Sunday.

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The earthquake occurred along the Queen Charlotte Fault – west of Haida Gwaii between two major plates – in an area that has experienced many large earthquakes in the past. But this is the first that has been well recorded by modern instruments, he said.

"We will learn a lot about how that fault behaves, where it slipped … and that will give us a better idea of where future earthquakes along that fault zone might occur and what type of movement and what type of ground shaking could result," Dr. Cassidy said.

The earthquake, which triggered tsunami warnings for coastal B.C., Alaska and Hawaii, provided a practice run to first responders in several communities and also raised questions about whether the province had moved quickly enough to inform the public.

On Twitter, users complained that it took Emergency Info B.C. nearly an hour to post information about the earthquake and tsunami advisories.

In Tofino, emergency personnel didn't hear from the province until 45 minutes after the quake, by which time Tofino officials had sounded tsunami sirens and activated a telephone alert system, Mayor Perry Schmunk said on Sunday.

B.C. Attorney-General Shirley Bond, the minister responsible for emergency management, said in a statement that the province was focusing first on communities closest to the quake.

Local governments are responsible for the initial response to emergencies and disasters. Emergency Management B.C., a provincial agency, provides advisories of active emergencies.

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Ms. Bond said the province will review its response times. "We'll look at response times and information flow, if we can improve it, we're going to do that," Ms. Bond said in an interview Sunday. "There were a couple of difficulties. We get our technical information from other sources, one of those websites had a glitch last night and that did cause a short delay."

By Sunday afternoon, more than 50 aftershocks had been recorded. Those aftershocks included a 6.4-magnitude quake 64 kilometres southwest of Sandspit at 11.:54 am on Sunday and a 5.0-magnitude jolt about 90 kilometres southwest of Sandspit a couple of hours later, at 2:38 pm. Neither resulted in a tsunami alert.

Earthquake experts say Pacific-wide tsunamis are less likely to be triggered by the horizontal slipping movement associated with earthquakes around the Queen Charlotte Fault than by earthquakes that result in vertical movement of the ocean floor, like a 2011 earthquake in Japan.

Any strong shaking, beneath land or ocean, has the potential to generate localized tsunamis.

"So it's really important for people to recognize that if they feel strong shaking, and they're close to the water - it's a good idea to move to higher ground," Dr. Cassidy said.

People felt the quake on Haida Gwaii, in coastal communities including Prince Rupert and further inland.

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In the low-lying community of Masset on Haida Gwaii, houses shook, trees swayed and residents were advised to move to higher ground.

Masset fire chief Stephen Grosse was getting ready to put on his costume for an annual Halloween dance at the fire hall when the earthquake hit. The floor shook, lamps fell over and he could see the floor of his house tremble. "You could barely stand. The house was just moving, you could physically see the floor moving," Mr. Grosse said on Sunday.

No significant injuries or property damage had been reported from the earthquake.

With a report from Justine Hunter in Whistler, B.C.

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