A spate of small earthquakes in B.C.'s remote northeastern corner were caused by a controversial technique used to extract natural gas from shale rock, says a report by the province's energy regulator.

The B.C. Oil and Gas Commission launched its probe after a "number of anomalous, low-level seismic events" were detected in the Horn River Basin, a gas-rich shale formation that's attracted some of the industry's biggest players.

"The investigation has concluded that the events observed within remote and isolated areas of the Horn River Basin between 2009 and 2011 were caused by fluid injection during hydraulic fracturing in proximity to pre-existing faults," the agency said in a recent report.

In order to break the rock and free the gas trapped inside of it, companies inject a combination of water, sand and chemicals underground at high pressure.

The process known as hydraulic fracturing, or fracking, has drawn concern from environmentalists and landowners for the amount of water the process requires and for potential contamination of groundwater.

Studies have also linked fracking to earthquakes around shale formations in England and Oklahoma.

The 38 events detected by Natural Resources Canada ranged between magnitudes of 2.2 and 3.8 on the Richter scale. A quake of between 4.0 and 4.9 is considered "light" and may cause a noticeable shaking of indoor items and rattling noises.

Only one of the quakes was felt at the surface by "workers in the bush" on May 19, 2011 and there have been no reports of injury or property damage.

"In undertaking the investigation, the commission notes that more than 8,000 high-volume hydraulic fracturing completions have been performed in northeast British Columbia with no associated anomalous seismicity," the report said.

The report said no quakes were recorded in the area prior to April 2009.

It said all of the events began after fracking took place. The quakes happened within five kilometres of fracking operations and within 300 metres of the depth at which the rock was being fractured.

Among other things, the report recommends improvements in seismic detection in the area, further study to identify pre-existing fault lines and stronger monitoring and reporting procedures.

It also calls for an examination of the relationship between hydraulic fracturing parameters and seismic activity. For instance, lower pump rates or injection volumes may be considered.

"It is essential to take pre-emptive steps to ensure future events are detected and the regulatory framework adequately provides for the monitoring, reporting and mitigation of all seismicity related to hydraulic fracturing, thereby ensuring the continued safe and environmentally responsible development of shale gas within British Columbia," said the report.

The Canadian Association of Petroleum Producers welcomed the report's recommendations, acknowledging that seismic activity associated with oil and gas extraction is of concern to the public.

Dave Collyer, president of the energy industry group, said natural gas companies provided the commission with data for its study and support its conclusions. The industry is finalizing guidelines for operators and is financially supporting more seismic monitoring in the region.

"Continuing our record of no harm to people or structures is paramount, as is supporting geoscience that can assure landowners and the public hydraulic fracturing can and will continue safely."