B.C.'s energy regulator is investigating a cluster of earthquakes in a busy gas drilling area of the province, CBC News has learned.

Since 2009, more than 30 earthquakes have been registered in the Horn River area, a region that has also seen extensive drilling and a process called hydraulic fracturing used by companies extracting natural gas.

Hydraulic fracturing, also known as fracking, involves injecting a pressurized mix of water and other substances into the rock to release trapped natural gas. The B.C. Oil and Gas Commission said it has not identified a direct link between hydraulic fracturing and the seismic activity, but is examining recent data collected from Horn River.

The coincidence of earthquakes and gas exploration warrants further investigation, said University of Calgary seismologist David Eaton.

"This would fall within the descriptor of a seismic swarm," Eaton told CBC News. "I think, you know, any links to hydrocarbon extraction of fluid injection would be really interesting."

Felt ground shake

Fort Nelson medic Tim Leavitt has felt the ground shake.

"It was brief, maybe lasted two, three seconds," said Leavitt. "It almost felt like a piece of equipment had hit my truck."

Halfway River Indian band Chief Ed Whitford also has felt the effects.

"It shook so bad it had all the rocks falling into the river," Whitford said.

Critics of fracking have said there could be hidden costs behind the practice and are calling for a moratorium until the science is in.

"It's responsible and good government to know what you're doing before you start blowing things up way underground," said Alberta's NDP environment critic Rachel Notley.

The process has already been banned in several jurisdictions, including the state of New York and France, and there are temporary moratoriums in place in New Jersey and Quebec.

With files from the CBC's Robert Doane