Series of earthquakes in northern Alberta felt in Edmonton, Grande Prairie and B.C.

Three of the largest earthquakes ever recorded in Alberta rattled the province on Tuesday and aftershocks continued for hours afterward.

Earthquakes Canada said a string of seismic events rumbled through northwestern Alberta.

The largest, shortly before 6 p.m. MT, was initially measured at magnitude 5.8. It was followed by a series of aftershocks.

Earthquakes Canada later revised the magnitude of the largest quake to 5.1.

The quakes were all detected near Reno, Alta., a rural hamlet 360 kilometres northwest of Edmonton in the Peace River region. Reno is 200 km northeast of Dawson Creek, B.C.

The tremors were felt in communities across the province. 

"Strongly felt close to Reno," reads a post on the Earthquakes Canada website. "Lightly felt in eastern British Columbia and western Alberta. There have been a number of felt aftershocks in the same area." 

A 5.0-magnitude aftershock was detected around 7:55 p.m. MT and was "lightly felt" by some residents in the area. 

In a statement Wednesday, the Alberta Energy Regulator said at least 14 seismic events had been detected in the Peace River region over a 24-hour period. The largest was measured at a depth of six kilometres, the AER said.

A preliminary investigation by the AER has determined the tremors were likely caused by natural tectonic activity.

There is no active hydraulic fracturing activity in the area, the regulator said, and there was no clear correlation to other energy activity in the area as operators in the area have not changed water injection volume over the past year.

"The data we currently have is showing the events as occurring at greater depths than what we would expect in the case of an induced event," the regulator said in a statement. 

The province's strongest natural earthquake — magnitude 5.4 — occurred in April 2001 near the Alberta-B.C. border, about 40 km northeast of Dawson Creek, B.C.

"Alberta is no stranger to earthquakes but earthquakes in Alberta don't tend to be this high," said Joseph Farrugia, a seismic analyst with Natural Resources Canada.

"This is certainly one of the largest earthquakes that occurred in Alberta. 

"It's uncommon and certainly scary for people who live in the area."

Farrugia said smaller aftershocks are possible over the next few days, though they won't all be felt. 

"These earthquakes do occur naturally, just due to faults being present underground and when those stresses change and those faults decide to release that energy, earthquakes happen."

Industrial activity likely not to blame

Stephen Crane, a seismologist with Natural Resources Canada, said Tuesday's earthquakes were likely naturally occurring, not triggered by industrial activity such as fracking.

He said the depth of the tremors indicates they were triggered by natural shifts in faults deep in the Earth. He said researchers will now be working to better map the underground geology of the area. 

"There are faults all over Canada. A lot of these faults are inactive and we wouldn't know about most of them, particularly these ones because that happened at several kilometres depth," he said. 

"It's likely that these did occur on a fault that we didn't know about but that's something that we will start investigating."

Reports from citizens show the biggest earthquake was also felt in Edmonton, Calgary and Fort McMurray and other communities in Alberta and northern B.C.

"The geology east of the Rocky Mountains is such that it favours the transmission of seismic energy much more easily than in the Rocky Mountains and in B.C. where the geology is pretty complicated," said Farrugia.

"So it's not surprising that this earthquake would be felt at great distances."

Shifting ground

Yu Jeffrey Gu, a seismologist at the University of Alberta, said he felt "a jolt" from one the earthquakes while driving in Edmonton with his son.

He said that a potentially damaging earthquake like the largest on Tuesday is relatively rare in Alberta. He expects aftershocks may continue for months.

The depth of the quake means it was likely caused by shifting rock formations, Gu said.

Fracking-induced earthquakes are more shallow and also exhibit unique strike-slip tectonic patterns that can be detected by seismographs.

Gu said earthquakes have been occurring in the Peace River region with greater frequency and there are ongoing efforts to increase monitoring in the area.

It's unclear why activity is increasing but the geological structure of the region, which includes the Peace River Arch, one of only a few large-scale tectonic elements in the Western Canada Sedimentary Basin, could be shifting, Gu said. 

"It's likely to be natural but the verdict is still out and a lot more research needs to be done."

'Things were shaking'

Carmen Langer, a farmer in Three Creeks, Alta., about 40 km north of Reno, said his house shook.

"I was coming up my stairs from downstairs and I felt really weird on the stairs," Langer said. "And then I come up and got in my kitchen and things were shaking and [the] chandelier was moving and lamps are moving."

Before Tuesday's earthquakes, at least three other events were recorded in the Reno area within the last week — two 4.1-magnitude quakes and one that measured 4.5.