High-Resolution Imaging of Hydraulic-Fracturing-Induced Earthquake Clusters in the Dawson-Septimus Area, Northeast British Columbia, Canada

Abstract

Abstract The number of earthquakes in the western Canada sedimentary basin (WCSB) has increased drastically in the last decade related to unconventional energy production. The majority of reported earthquakes are correlated spatially and temporally with hydraulic fracturing (HF) well stimulation. In this study, we use waveform data from a new deployment of 15 broadband seismic stations in a spatial area of roughly 60×70km2, covering parts of the Montney Formation, to study the relationship between earthquakes and HF operations in the Dawson-Septimus area, British Columbia, Canada, where the two largest HF-related earthquakes in WCSB to date, an Mw 4.6 on 17 August 2015 and an ML 4.5 on 30 November 2018, have occurred. We use an automated short-term average/long-term average algorithm and the SeisComP3-software to detect and locate 5757 local earthquakes between 1 July 2017 and 30 April 2019. Using two clustering techniques and double-difference relocations of the initial catalog, we define event families that are spatially associated with specific wells, and exhibit temporal migration along a horizontal well bore and/or multiple fractures close to wells. Relocated clusters align in two dominant orientations: one roughly perpendicular to the maximum horizontal regional stress direction (SH) and several conjugate structures at low angles to SH. Comparing the two predominant seismicity lineations to regional earthquake focal mechanisms suggests that deformation occurs via thrust faulting with fault strike oriented perpendicular to SH and via strike-slip faulting with strike azimuth at low angles to SH. Local scale seismicity patterns exhibit clustering around individual HF wells, whereas regional scale patterns form lineations consistent with deformation on faults optimally oriented in the regional stress field.