Fracking linked to most induced earthquakes in western Canada

and colleagues found thirty-nine hydraulic fracturing wells (0.3 percent of the total of fracking wells studied), and seventeen wastewater disposal wells (1 percent of the disposal wells studied) that could be linked to earthquakes of magnitude 3 or larger.

While these percentages sound small, Atkinson pointed out that thousands of hydraulic fracturing wells are being drilled every year in the WCSB, increasing the likelihood of earthquake activity. “We haven’t had a large earthquake near vulnerable infrastructure yet,” she said, “but I think it’s really just a matter of time before we start seeing damage coming out of this.”

The study also confirmed that in the last few years nearly all the region’s overall seismicity of magnitude 3 or larger has been induced by human activity. More than 60 percent of these quakes are linked to hydraulic fracture, about 30-35 percent come from disposal wells, and only 5 to 10 percent of the earthquakes have a natural tectonic origin, Atkinson said.

Atkinson said the new numbers could be used to recalculate the seismic hazard for the region, which could impact everything from building codes to safety assessments of critical infrastructure such as dams and bridges. “Everything has been designed and assessed in terms of earthquake hazard in the past, considering the natural hazard,” she said. “And now we’ve fundamentally changed that, and so our seismic hazard picture has changed.”

The researchers were also surprised to find that their data showed no relationship between the volume of fluid injected at a hydraulic fracturing well site and the maximum magnitude of its induced earthquake.

“It had previously been believed that hydraulic fracturing couldn’t trigger larger earthquakes because the fluid volumes were so small compared to that of a disposal well,” Atkinson explained. “But if there isn’t any relationship between the maximum magnitude and the fluid disposal, then potentially one could trigger larger events if the fluid pressures find their way to a suitably stressed fault.”

Atkinson and her colleagues hope to refine their analyses to include other variables, such as information about extraction processes and the geology at individual well sites, “to help us understand why some areas seem much more prone to induced seismicity than others.”

The scientists say the seismic risks associated with hydraulic fracturing could increase as oil and gas companies expand fracking’s use in developing countries, which often contain dense populations and earthquake-vulnerable infrastructure.

— Read more in “Hydraulic Fracturing and seismicity in the Western Canada Sedimentary Basin,” Seismological Research Letters (29 March 2016)