Geoscientists have revealed a direct link between hydraulic fracturing, or fracking, and earthquakes in Canada. The groundbreaking study found that earthquakes can even occur intermittently over several months after drilling operations end.

Seismicity of northwestern Alberta, Canada for the period 1985−2016. The size of the dot correlates to the magnitude of the earthquake. Xuewei Bao and David Eaton

According to a new study published in the journal Science, seismic activity in northwest Alberta over the last five years were likely caused by fracking, in which chemically-laden water and sand is injected at high pressures into shale formations to release oil or gas.

The article, Fault activation by hydraulic fracturing in western Canada, was authored by Xuewei Bao and David Eaton from the University of Calgary.

For the study, the researchers mapped out more than 900 seismic events near Duvernay shale drilling sites around the Fox Creek area dating back to December 2014. This included a 4.8-magnitude earthquake in January in northern Alberta that's likely the strongest fracking-induced earthquake ever.

They found that there were two main causes for quakes. The first was immediately from pressure increases as the fracking process occurred.

"We were able to show that what was driving that was very small changes in stress within the Earth that were produced by the hydraulic fracturing operations," Eaton told DeSmogBlog.

The second cause comes from pressure changes from lingering fracking fluid. According to the Globe and Mail, a fault shakes when fluids infiltrate tiny spaces in the porous rock and increases pore pressure.

"If that pressure increases, it can have an effect on the frictional characteristics of faults," Eaton told the Globe and Mail. "It can effectively jack open a fault if the pore pressure increases within the fault itself and make it easier for a slip to initiate."

Per the study abstract, "Patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of >1 km, whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months."

Eaton told DeSmogBlog that a "majority of injection-induced earthquakes are actually linked to hydraulic fracturing" in Canada.

The new study is not related to the recent spate of induced earthquakes currently rocking midwestern states, most notoriously Oklahoma. Those quakes are not likely caused by fracking itself but from the injection of large volumes of oil and gas wastewater into deep underground wells.

"The key message is that the primary cause of injection-induced seismicity in Western Canada is different from the central United States," Eaton told the New York Times, adding that their study could help regulators craft guidelines to avoid more human-caused earthquakes.