Fault orientations of multiple earthquake sequences induced by hydraulic fracturing in the Dawson-Septimus area, northeast British Columbia, Canada
Abstract
An increasing number of M3+ earthquakes in the last decade has been associated with hydraulic fracturing (HF) in low-permeability tight shale in the Western Canada Sedimentary Basin (WCSB), including a Mw 4.6 on 08/17/2015 near Ft. St. John, and a ML 4.5 on 11/30/2018 near Dawson Creek. Here, we use a deployment of 15 (dominantly broadband) seismic stations in an area of roughly 60 x 70 km2 in Dawson-Septimus in close proximity to numerous HF wells in the time period between July 2017 and December 2018 for detailed seismic monitoring. In total, we detect 3498 local earthquakes, of which 2723 surpass a quality control criterion of having a horizontal location error ≤ 3 km. In order to investigate the correlation between injection and earthquake initiation, we explore event similarity of 18 groups of earthquakes that correlate with individual injection episodes at specific wells and exhibit similar patterns in daily cumulative seismic moment. We perform event clustering within the 18 groups using two clustering methods: one based on waveform similarity, and the second on space-time-energy distances. As individual families may represent the activation of specific geological structures, we perform double-difference relative relocation to image fault orientations based on seismicity. We also invert for focal mechanism solutions per event cluster to see whether they are consistent with seismicity lineations or structures inferred with relative relocations.
Among the 18 groups of events, 25 clusters correlate with individual stimulation phases. Processing each earthquake cluster separately allows us to successful relocate 2386 out of the total 2723 events. Relocated clusters align in two dominant orientations, one roughly perpendicular to SH and several conjugate structures sub-parallel to SH. Focal mechanism solutions for events with M > 2.8 in the 11/30/2018 ML 4.5 sequence are consistent with the two lineations implied by relative relocations being optimally oriented in the regional stress field, i.e. thrust faulting with strike oriented perpendicular to SH, and strike-slip faults with strike azimuth at low angles to SH. Our results thus suggest at the local scale induced seismicity cluster around individual HF wells while at the regional scale they form lineations dictated by the regional stress orientation.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S13E0479R
- Keywords:
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- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8164 Stresses: crust and lithosphere;
- TECTONOPHYSICS