Fox Creek, an oil town of nearly 3,000 residents in western Alberta, recently experienced its third earthquake of at least magnitude 4.0 this year. The difference between this one and many of the quakes felt in fracking country in the U.S., however, is that Canadian researchers are attributing the cause to fracking itself, not just the wastewater disposal process.

The reported 4.4-magnitude event that jolted the region in mid-June was the latest in a surge of seismic events that ramped up in December 2013, around the time fracking increased in this part of Alberta. There was no reported damage, but Chevron Corp. temporarily shut down its drilling operations nearby.

In western Canada, similar to parts of the central United States, one of the emerging side effects of the fracking boom is what scientists call "induced seismicity" — the proliferation of suspected man-made earthquakes.

In Canada, though, scientists and regulators now believe the dominant trigger of induced earthquakes affecting western Alberta, including Fox Creek, and parts of British Columbia, is the fracking itself—the pumping of huge amounts of chemicals, water and sand down a well to crack open bedrock to release oil and gas.

"Even a year ago, there was a fairly widely held view that almost all of the induced earthquakes [across North America] were coming from wastewater disposal and that hydraulic fracturing has very limited potential to induce earthquake," said Gail Atkinson, professor and Canada Research Chair in Earthquake Hazards and Ground Motions at the University of Western Ontario.

Despite the growing awareness about fracking-caused quakes in Canada, "what's less clear is how much of the seismicity in the U.S. might be tied to hydraulic fracturing," said Atkinson. "I think there's so much of it from wastewater disposal, it may be masking an underlying signal from hydraulic fracturing."

George Choy, a seismologist at the United States Geological Survey, told InsideClimate News that fracking-caused events are "rare" in America. He could name only two examples: a cluster of 77 earthquakes felt in Poland Township, Ohio, in March 2014 and a series of 116 earthquakes that occurred in south-central Oklahoma in January 2011. Meanwhile, there have been thousands of seismic clusters across the central United States in recent years that scientists suspect are tied to wastewater injection.

Cause, or Coincidence?

Fox Creek is one of the emerging seismic hot spots in western Alberta and northeastern British Columbia, providing an opportunity for Canadian researchers to investigate this less-understood type of induced seismicity.

At first glance, fracking quakes and wastewater quakes are triggered in a similar manner: They both involve the injection of fluid underground in an area with existing faults.

But, according to Jeffrey Gu, an associate professor of geophysics at the University of Alberta, there are some key differences. For one, fracking-caused events likely occur more quickly after fluid injection—on the order of hours to days to weeks. Wastewater events, however, can occur months to years later.

Gu, Atkinson, and three other researchers found this to be the case in Fox Creek in 2013, when the area was struck by an unusually high number of earthquakes—more than 50 quakes in a four-month period. "If you look at the time of the hydraulic fracturing of the operations, the timing of the earthquakes is closely related," said Atkinson.

Scientists suspect it involves the different nature of the injection. For fracking, the injection of fluids—a slurry cocktail of chemicals, water and sand—is done at a high pressure over a short period of time, and eventually much of that water is pumped back up. In contrast, wastewater is dumped down a well at low pressures, consistently, for months to years.

The 2015 Fox Creek events shattered the notion that fracking-triggered earthquakes are always small, said Atkinson. Fox Creek potentially set the record for the largest quake likely tied to fracking with a magnitude 4.4 event on Jan. 22. A week prior, the same area experienced a 4.0-magnitude event.

The Fox Creek events caught the attention of the Alberta Energy Regulator, which responded by releasing new rules dictating operator response to earthquakes.

Companies with fracking sites around Fox Creek are now required to report an earthquake of magnitude 2.0 or greater that is felt within about 3 miles of their operation. If the event measures 4.0 or above in magnitude, the operator should shut down.

This response is called a "traffic-light system," and is used by regulators in response to induced earthquakes in both Canada and the United States.

Earlier this week, three earthquakes with magnitudes ranging between 4.0 and 4.5 shook Oklahoma. Since then, state officials have announced that two wastewater-disposal wells have been temporarily shut down.

Alberta's rules were first put to the test following the earthquake in mid-June. Chevron was the closest operator to the earthquake origin, and immediately closed down its facility. Chevron had completed fracking at this location on June 5 and was working on construction at the time of the earthquake. The company received regulatory approval to restart on June 30.

So far, none of the suspected induced seismic events in western Canada have caused any damage. It's a different story in the United States, where events possibly linked to wastewater disposal have resulted in cracked buildings and collapsed chimneys, and impacted residents repeatedly have attempted to sue energy companies for compensation.

In Canada, "the public is of two minds," said Atkinson. Take Fox Creek: "on the one hand, people are really getting quite concerned over the possibility of damage ... but on the other hand, the town's economic forces are closely tied to the oil-and-gas industry." People don't want the industry to go away, said Atkinson––they just want it to be "a little more careful."