A pair of central Alberta winter earthquakes has triggered a ban against hydraulic fracturing (fracking) in deep oil and natural gas wells around a power dam and reservoir 144 miles southwest of the provincial capital in Edmonton.

The Alberta Energy Regulator (AER) enacted a no-fracking zone that restricts use of the shale production method around the 365 MW Brazeau Dam and its 31 square-mile reservoir.

The new order bans the practice in wells that target the deep Duvernay Shale within a three mile-wide safety ring. Fracking is also prohibited in shallower wells within 1.8 miles of the dam and reservoir.

In the tolerated shallow wells, the AER requires seismic event monitoring and response procedures, reporting of tremors exceeding magnitude 1.0, and a halt to operations if the shaking tops 2.5 on the earthquake scale.

The AER described the no-fracking zone as a precaution rather than an emergency response. No earthquakes attributed to the industry practice have been reported by the public or recorded by scientific instruments around the Brazeau Dam.

But the region includes a provincial recreational area and three campgrounds. Central Alberta is a prolific gas and oil production area. An industry drilling operations base, Drayton Valley, is just 33 miles from the Brazeau Dam.

Public safety concerns were aroused in March by central Alberta earthquakes 140 miles southeast of Brazeau Dam at Sylvan Lake and 100 miles south of the reservoir at Rocky Mountain House.

The winter tremors exceeded magnitude 4.0 and were felt on the ground surface. Neither earthquake caused injuries or significant property damage. But both were interpreted as hazard warnings.

Investigations continue. The Sylvan Lake event was linked to drilling. The AER imposed restrictions. No association with industry was found in the Rocky Mountain House case, where the tremor originated in different geology from typical drilling targets.