Source processes of injection‐induced earthquakes involve complex fluid‐rock interaction often elusive to regional seismic monitoring. Here we combine observations from a local seismograph array in the Montney Formation, northeast British Columbia, and stress modeling to examine the spatiotemporal evolution of the 30 November 2018 Mw 4.2 (ML 4.5) hydraulic fracturing‐induced earthquake sequence. The isolated occurrence of the mainshock at a depth of ∼4.5 km in the crystalline basement 2 days following injection onset at ∼2.5 km depth suggests direct triggering by rapid fluid pressure increase via a high‐permeability conduit. Most aftershocks are in the top 2 km sedimentary layers, with focal mechanisms indicating discrete slip along subvertical surfaces in an ∼1 km wide deformation zone. Aftershock distribution is consistent with static stress triggering from the Mw 4.2 coseismic slip. Our analysis suggests that complex hydraulic and stress transfer between fracture networks needs to be considered in induced seismic hazard assessment.

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.

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 ML > 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 SHmax, suggesting optimally oriented, left‐lateral faults. Reverse faulting nodal planes are roughly perpendicular to SHmax 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 ∼ML 2.0, likely due to observational bandwidth limitations.

Abstract. Passive seismic datasets are a key technology for exploration and monitoring of subsurface reservoirs. Searching for alternative resources in the framework of the energy transition creates a surge for identifying as many potential sites as possible suitable for geothermal exploitation. The Lower Rhine Embayment, at the western border of North Rhine-Westphalia in Germany, is an extensional system with a very high potential for geothermal exploitation. The area experiences moderate but continuous natural seismicity. Here, we report on a passive seismic dataset recorded with 48 seismic stations centred at and around Eschweiler-Weisweiler. Background seismic noise levels are high at this site due to high levels of anthropogenic noise and thick unconsolidated sedimentary layers. The final station layout is a compromise between targeted network design and suitably quiet locations. We show that the network design allows the application of state-of-the-art methods including waveform-based source location methods and ambient noise velocity imaging methods.