Source Properties of Hydraulic-Fracturing-Induced Earthquakes in the Kiskatinaw Area, British Columbia, Canada

This work presents a high resolution source property study of hydraulic fracturing induced earthquakes in the Montney Formation, a low-permeability tight shale reservoir in the Kiskatinaw area, northeast British Columbia, Canada. We estimate source parameters, including focal mechanism solutions (FMSs), seismic moment, spectral corner frequency, and static stress drop values of earthquakes recorded between July 2017 and July 2020. Waveform-similarity-based event classification of 8,283 earthquakes yields 52 event families (clusters) and 1,014 isolated events (individuals). We calculate a total of 64 FMSs of events M-L > 2.5 with high-quality waveforms. Of the 64 solutions, 54 come from events within families, and are used to infer an additional 3,500 focal mechanisms of smaller-magnitude events with similar waveforms. The other 10 are isolated events. The dominant faulting style inferred from FMSs highlights multiple cascading, shallow, strike-slip events and generally isolated, larger-magnitude reverse-style events in close proximity to the Fort St. John Graben system. Inferred nodal planes of strike-slip events are at low-angles to regional S-Hmax, suggesting optimally oriented, left-lateral faults. Reverse faulting nodal planes are roughly perpendicular to S-Hmax and have an orientation consistent with the reactivation of pre-existing normal basement faults. Source spectral analysis using three approaches, including spectral-ratio fitting, suggests a constant stress drop of 1-10 MPa and self-similarity for induced events. Constant stress drop scaling breaks down at magnitudes smaller than similar to M-L 2.0, likely due to observational bandwidth limitations.