Study suggests that bedrock is an earthquake factor caused by fracking

New research shows why sinter fracturing causes earthquakes in some regions but not in others.

An article published Monday in Geophysical Research Letters suggests that the probability of an artificial earthquake is strongly influenced by the stability of the ground before the energy industry is manifested.

"Some places seem to be particularly sensitive to [artificially-]Honn Kao, a seismologist with the Geological Survey of Canada and lead author, explains Honn Kao.

Scientists have long known that the injection of fluids to evacuate wastewater or to release underground reserves of oil and gas can cause earthquakes.

Regulatory records show that there have been hundreds of seismic events since 2015 in a highly fractured region of northwestern Alberta.

The earthquakes around Fox Creek recorded a magnitude of 4.5 on the Richter scale – strong enough to rattle dishes and images.

The energy regulator of Alberta has tightened the restrictions on fracking in the region.

Meanwhile, other regions see thousands of wells fractured while the earth remains motionless.

Although the link between fracking and earthquakes is well established, its functioning remains mysterious.

Other studies have asked if this was related to local geology or particular fracking practices, but Kao said that he had found a much larger contributor.

"The background tectonic charge rate seems to be one of the predominant factors controlling the region's response to injection-induced earthquakes," he said.

Voltage "stored as a coil spring"

In other words, the deep, underground movement of the Earth's rocky tectonic plates creates areas where the tension is concentrated and stored as a coiled spring, called tectonic deformation. Sudden fragmentation of the rock by fracturing or injection of wastewater under high pressure releases this accumulated energy in the form of an earthquake.

The discovery could help explain why western Alberta and northeastern British Columbia. have a high rate of fracturing-induced earthquakes, and places like Saskatchewan, which has thousands of fractured wells, do not have it.

"The Canadian side of the Rockies has a much higher rate of tectonic deformation," said Kao. "As you move from the Canadian Rockies to the east, the rate of deformation decreases quite rapidly."

Of all the fracture-induced earthquakes studied by him and his colleagues, 98% occurred in a 150-km stretch of the Rockies, where the underground rocks are naturally subject to stress.

These stresses are not the only cause of earthquakes.

Artificial temblors are common in Oklahoma, where underground tension is low in Alberta.

But there, said Kao, fluid injection can be important enough to cause problems by itself. Injection rates are 100 times higher than in Canada, he said.

Underground stress

Underground stress is probably best understood as a major contributing factor, Kao added.

"It's more of a competition of all these different factors."

The work has implications for how fracking should be regulated, Kao said. It may be necessary to modify the regulations in different regions, depending on the depth tectonic tension.

Kao said that in theory, these small artificial earthquakes could be a good thing. They may be relieving tensions that might otherwise lead to a bigger and more dangerous event.

"We are reducing the occurrence of the future major earthquake," he said. "Theoretically."