Between April 2009 and December 2011, 38 were reported by NRCan, and another 234 recorded by seismographs in the Etsho and Kiwigana areas, ranging from 2.2 to 3.8 on the Richter scale. Only one of those events was felt at the Earth's surface, and there were no injuries or damage caused. The Commission's geological and engineering staff determined that those small earthquakes had been caused by the fluid injection process of hydraulic fracturing near pre-existing faults.
"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," writes the OGC in its report.
All 38 NRCan reported events occurred either during a hydraulic fracturing stage or sometime after one stage ended and another began, with none recorded before or after operations. The magnitude and frequency of each recorded seismic activity may be dependent upon numerous factors like the pump rate, breakdown pressure and proximity to pre-existing faults.
Before this, the only documented case of oil and gas activity causing seismicity in B.C. occurred in the Eagle Field area, approximately five kilometres north of Fort St. John. 29 seismic events, ranging from 2.2 to 4.3 in magnitude, from November 1984 to May 1994. Hydraulic fracturing was not being used in the area at the time, but it was determined high pressure fluid injection for secondary oil recovery was a possible cause. That discovery caused the injection pressure to be lowered, and now have to remain below a certain level.
As a result of the investigation, the Commission has made seven recommendations, which include improving the accuracy of the Canadian National Seismograph Network in northeast B.C., performing geological and seismic assessments to identify pre-existing faulting, establishing induced seismicity monitoring and reporting Procedures and Requirements, and stationing ground motion sensors near selected northeast B.C. communities to quantify risk from ground motion.
"The recommended ground motion sensors will accurately record any ground acceleration from future events," write the OGC. "This enables a correlation between magnitude and any ground motion and eliminates the need to rely on ‘felt’ reports to gauge possible effects at surface."
The OGC says it will study the deployment of a portable dense seismograph array to selected locations where induced seismicity is anticipated or has occurred, and look into the relationship between hydraulic fracturing parameters and seismicity. It also recommends requiring the submission of micro-seismic reports to monitor hydraulic fracturing for containment of micro fracturing and to identify existing faults.
"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," the report concludes.
The full report is available for download below.