No abstract

A rapid increase of injection-induced earthquakes (IIE) is often linked to a higher level of seismic hazard. In this study, we compare the geodetically defined moment rate to seismicity distribution in western Canada where significant IIE are observed. The regional seismic pattern is dominated by IIE, both in number and moment, along a 150-km wide NW-SE band of moderate strain rate in the easternmost Cordillera and foothills. The observed rate of moment release from local earthquakes is much closer to the tectonic moment rate in the IIE-dominated areas. We conclude that, on a regional scale, tectonic strain rate is an important control on IIE. Injection in areas with moderate tectonic strain may temporarily increase the local seismic hazard, but widespread IIE over an extended period of time may deplete the available tectonic moment and could, under the right conditions, have a limited long-term effect of reducing regional seismic hazard.Plain Language Summary Fluids are commonly injected into oil and gas wells to shutter the reservoir formations of shale gas and tight oil and to increase production. However, not all injections cause induced earthquakes and some areas have more events than others. In this study, we examine the geological controls on where there is greatest susceptibility to induced earthquakes. In western Canada, we find that they are generally associated with the areas of moderate long-term geological/tectonic deformation rates, as mapped by the relative motion of high-resolution Global Navigation Satellite System stations. Most induced earthquakes are in a 150-km-wide band in the easternmost Canadian Cordillera and foothills. They are much less frequent farther to the east where the geological deformation rates are low. We conclude that the geological deformation rate is an important controlling factor for the occurrence of induced earthquakes. In some areas, the strain rate from induced earthquakes may temporarily exceed the natural geological strain rate. Widespread injections in areas with relatively high geological deformation rate may increase the regional seismic hazard in the short term. But if frequent occurrence of induced earthquakes persists over time, it could lead to a reduction of natural earthquake occurrence in the long term.

To gain a better understanding of induced seismicity in northeast British Columbia and western Alberta, we conducted an intensive analysis of seismic data to locate earthquakes that occurred within the area of 52°N-61°N, 126°W-115°W for the years of 2014 through 2016. Continuous seismic waveforms from as many as 43 stations operated by various organizations in the region were used in this study. A total of 5478 events were identified and located; but only 4916 solutions were deemed acceptable by our quality criteria. The number of earthquakes in our final catalogue is approximately three times the base level of the Canadian National Seismograph Network catalogue. In this report, we describe in detail our location procedures and how each source parameter (origin time, epicenter, focal depth, and magnitude) is determined. The earthquake catalogue is summarized in a table, while the phase picking data for individual events are presented in an ASCII file as a supplement to this report. The total numbers of events in 2014, 2015, and 2016 are 1287, 1575, and 2057, respectively. The overall magnitude of completeness of our catalogue is ML 1.8, an improvement from the value of 2.3 for the CNSN catalogue.