Rate of earthquakes depends on volume of fluids in hydraulic fracturing operations – but the magnitude of the largest possible events does not

New findings published by the high impact journal Science show that the rate in which earthquakes are triggered or induced by fracking depends on the volume of the hydraulic fracturing operations. But the magnitude of the triggered events is not capped – contrary to a concept which is still widely held.

Gail Atkinson, a professor in Western University’s Faculty of Science and the NSERC/TransAlta/Nanometrics Industrial Research Chair in Hazards from Induced Seismicity, teamed with researchers at the Alberta Geological Survey, the University of Alberta, the University of Calgary and Natural Resources Canada to show how seismicity is linked to fracking.

Atkinson, an internationally renowned expert on earthquakes and seismic hazards, and her collaborators have previously proven that there is a clear correlation between earthquakes at the magnitude 3.0 and above and industrial hydraulic fracturing operations.

But the latest results show a direct link between larger volumes of hydraulic fracturing fluids in the Duvernay play, a geological region in central Alberta that holds Canada’s largest marketable reserves of oil, and a higher number of induced earthquakes.

“This is an important finding because some previously held theories propose that there is a relationship between the largest magnitude of the earthquake and the injected volume, but what we have found is that the maximum magnitude isn’t what’s being controlled by the volume, it’s the earthquake rate,” says Atkinson, who notes that these two theories are slightly related because the more earthquakes that are induced provide more opportunities for a larger one to occur.

Atkinson says this is imperative information for industry as hydraulic fracturing operations can now control the rate of earthquakes and therefore, the number of larger ones, by controlling volume. But this discovery comes with a warning.

“Industry needs to be aware that controlling the volume doesn’t provide a guarantee on the maximum magnitude,” says Atkinson. “There is still a possibility for larger events so industry still needs to be very careful where they conduct hydraulic fracturing operations. They have to stay away from critical infrastructure to prevent a damaging event.”

According to Atkinson, there are promising signs that industry can change or modify existing practices to still get the results that they want, while reducing the number of induced earthquakes that they cause.

“There is some indication that industry is getting better at limiting induced earthquakes as the number of induced events has gone down in a number of jurisdictions, like Alberta and Oklahoma, over the past year,” says Atkinson. “For a while, every year, the largest event that was induced was the largest to date and we haven’t seen anything bigger this year than we have before. That may be a sign that industry is figuring some of these things out.”

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