Some 90% of earthquakes in Western Canada are caused by human activity, with most induced by fracking, a new seismological study suggests.
Gail Atkinson from Western University in Canada and colleagues traced earthquakes in the region for 20 years and found 60% were linked to fracking, while 30-35% were due to wastewater disposal. Their work was published in Seismological Research Letters.
Western Canada, which comprises the provinces Alberta, British Columbia, Manitoba and Saskatchewan, contains around 13% of the world’s oil reserves and is dotted with thousands of wells. In a bid to suck as much out of the ground as possible, hydraulic fracturing – or “fracking” – is widely used.
Fracking is a controversial technique, and it’s not hard to see why. It involves injecting fluid under high pressure into the ground, shattering rocks, and releasing oil and gas trapped within rock pores.
Amid fears of contaminating the underlying water table, fracking can also force open existing natural faults to produce earthquakes. On 12 January this year, a magnitude 4.2 earthquake hit the small town of Fox Creek in Alberta – a quake that was caused by fracking operations nearby.
But wastewater disposal is another ground-shaker. In the US, the practice causes more quakes than fracking. When oil is sucked out of the Earth, it’s not usually pure. Most of the time it’s mixed with solids and water. Once separated, the water is squirted back into empty wells for permanent storage.
Huge amounts of water are reinjected – far more than the fluids used in fracking.
So to see what proportion of Western Canadian earthquakes are due to fracking or wastewater disposal, Atkinson and her colleagues compared the relationship of 12,289 fracking wells and 1,236 wastewater disposal wells to magnitude 3 or larger earthquakes in an area of 454,000 square kilometres near the border between Alberta and British Columbia, between 1985 and 2015.
Statistical analyses identified earthquakes as being related to fracking if they occurred close to a well and within a window spanning the start of fracking to three months after completion.
They found 39 hydraulic fracturing wells (0.3% of the total of fracking wells studied) and 17 wastewater disposal wells (1% of the disposal wells studied) could be linked to earthquakes of magnitude 3 or larger.
Atkinson pointed out that even those the numbers sound small, thousands of hydraulic fracturing wells are being drilled every year in the area, 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.”
While there didn’t seem to be a relationship between the amount of injected fracking fluid and earthquake magnitude, the study confirmed that in the past few years nearly all quakes of magnitude 3 or larger were induced by human activity.
More than 60% of these quakes are linked to hydraulic fracture, 30-35% come from disposal wells, and only five-10% of the earthquakes have a natural tectonic origin, Atkinson said.
“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,” she 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.”
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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