January 11, 2019 by THE CANADIAN PRESS
GRAND BAY-WESTFIELD, N.B. – A minor earthquake rattled windows and knocked dishes off shelves in a small community in southern New Brunswick on Thursday.
“It felt like something ran into the building _ it was a big bang,” said Troy Gautreau, chief of Grand Bay-Westfield Fire and Rescue, who was in Fire Station No. 1 when the quake struck.
“It went on for three or four seconds. It was long enough to really grab your attention.”
Federal officials say the 3.8-magnitude quake was recorded at 9:49 a.m., its epicentre in the community of Grand Bay-Westfield, about two kilometres underground and about 25 kilometres north of Saint John.
Gautreau confirmed there were no reports of damage, but many residents called the town office to find out what was going on.
Firefighters were dispatched to one home, where the occupants thought their basement had exploded.
Earthquakes Canada, a branch of the Natural Resources Department, said local residents had filed more than 250 online reports about the seismic activity by early afternoon.
Nick Ackerley, a seismologist with Earthquakes Canada, said the epicentre of the quake was relatively shallow, which is why so many people felt the rumbling.
He said earthquakes at this magnitude typically cause little damage, unless they are close to a heavily populated area.
“Even in that case, we expect very light damage,” he said. “But we know that it was widely felt.”
In 1982, New Brunswick experienced its most powerful earthquake on record, a 5.7-magnitude shaker in the Miramichi region that was 100 times more powerful than the one recorded on Thursday.
“But it only caused light damage because there were very few people living close to the epicentre,” Ackerley said.
The latest quake could have been the result of intraplate tectonics, which refers to the fact that all of Eastern Canada is in the middle of one tectonic plate known as the North American Plate, he said.
Even though there are no active stress points in the middle of this rather stable plate, there are many faults caused by the creation of the Appalachian Mountain Range 250 million years ago, and the opening of the Atlantic Ocean 200 million years ago.
“Those major tectonic events created lots of faults in the region, but they’ve been inactive since then,” Ackerley said.
As well, some seismic stress can be traced to massive glaciers that retreated from Eastern Canada more than 20,000 years ago, which allowed the Earth’s crust to slowly bounce back.
“So it’s still rebounding,” he said. “That’s where some of the stress in the rock comes from.”
Last April, the federal agency said it recorded 22 earthquakes in New Brunswick during a 30-day span, most of them felt near McAdam, on the western edge of the province.
In early 2016, a “swarm” of more than 100 earthquakes shook the McAdam area, but a reason was never found.
Local residents said the quakes often produced a loud bang, similar to a gunshot. Some said it sounded like their hot water tank had exploded.
Most of those earthquakes rated at less than three in magnitude, as calculated on a scale developed by Otto Nuttli, a American seismologist whose formula is used to measure the energy released by earthquakes in eastern North America.
According to Earthquakes Canada, the better-known scale developed in California by Charles Richter does not apply to Eastern North America, where the seismic waves attenuate differently.
-By Michael MacDonald in Halifax