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A service rig sits ready next to pumpjacks on a well pad outside of Fox Creek, Alta., on July 2, 2015.Amber Bracken/The Globe and Mail

An energy company has stopped operating in a part of Alberta subject to heavy hydraulic fracking after the province's energy regulator reported the area's largest earthquake in more than a year.

"They have ceased operations and will not be able to resume until we have approved their mitigation plans," Carrie Rosa of the Alberta Energy Regulator said Tuesday.

Rosa said final readings of the quake's strength registered 4.8 on the Richter scale, which rates tremblors of that magnitude at the top of the "light" classification. They're likely to be felt by most people in the area and may cause noticeable shaking and rattling of indoor objects.

No injury or damage was reported from the quake, which occurred about 35 kilometres west of Fox Creek.

Rosa said Repsol Oil and Gas won't be able to resume operations until the regulator has approved its mitigation plans.

"We have to find out what was occurring at the time the seismic event happened," she said. "We have investigators on the way to the site."

Concerns about seismic activity in the Fox Creek area began in December 2014 when a series of 18 earthquakes between 2.7 and 3.7 in magnitude rumbled through. In January 2015, several shakers were recorded between magnitudes of 2.4 and 4.4.

The regulator responded in February by imposing new rules for the so-called Duvernay play near town.

"The order comes after several seismic events — possibly related to hydraulic fracturing — were recorded in the Fox Creek area," the regulator said in a news release at the time.

Under the rules, companies must consider the likelihood of resulting earthquakes before starting to frack. Any seismic events greater than 4.0 on the Richter scale require an operator to shut down and notify the regulator. Quakes between 2.0 and 4.0 don't prompt a shutdown, but an operator must still inform the regulator. No activity is required for anything less than 2.0.

The rules also require closer monitoring of seismic activity.

Alberta Premier Rachel Notley said she wants the regulator to speed up a review the NDP government has asked for into seismic activity in the area.

"My officials have been in touch with the AER to find out exactly what the situation is and we're waiting to get more details," Notley said in Edmonton.

"The AER has been engaged in a review of fracking, in particular as it relates to this issue, and I'll be asking them to speed that review ... to come up with some recommendations that we can consider sooner than later.

"What I'd like to see first of all is a report on what the evidence shows is the relationship between fracking and the seismic activity that we've observed up in Fox Creek."

The regulator's database shows there have been 366 seismic events in the region since January 2015.

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