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TitleAftershock decay rate of large injection-induced earthquakes in northeast British Columbia: a case study for two sequences in the Montney play
AuthorFarahbod, A M; Kao, HORCID logo
SourceCanadian Society of Exploration Geophysicists, Recorder 2019 p. 1-11
Alt SeriesNatural Resources Canada, Contribution Series 20190324
PublisherCanadian Society of Exploration Geophysicists
Mediaon-line; digital
File formatpdf
ProvinceBritish Columbia
NTS93O/01; 93O/02; 93O/03; 93O/06; 93O/07; 93O/08; 93O/09; 93O/10; 93O/11; 93O/14; 93O/15; 93O/16; 93P; 94A; 94B/01; 94B/02; 94B/03; 94B/06; 94B/07; 94B/08; 94B/09; 94B/10; 94B/11; 94B/14; 94B/15; 94B/16; 94G/01; 94G/02; 94G/03; 94G/06; 94G/07; 94G/08; 94G/09; 94G/10; 94G/11; 94G/14; 94G/15; 94G/16; 94H; 94I/01; 94I/02; 94I/03; 94I/04; 94I/05; 94I/06; 94I/07; 94I/08; 94J/01; 94J/02; 94J/03; 94J/06; 94J/07; 94J/08
AreaDawson Creek; Fort St. John; Chetwynd; Hudson's Hope
Lat/Long WENS-123.5000 -120.0000 58.4000 55.1000
Subjectsgeophysics; fossil fuels; environmental geology; engineering geology; Science and Technology; Nature and Environment; Economics and Industry; petroleum resources; petroleum industry; hydrocarbon recovery; hydraulic fracturing; waste disposal; seismology; earthquakes; earthquake magnitudes; seismicity; aftershocks; bedrock geology; structural features; fractures; lithology; sedimentary rocks; siltstones; sandstones; dolostones; Montney Formation; Canadian National Seismograph Network; Waste water; cumulative effects
Illustrationslocation maps; geoscientific sketch maps; time series; photographs
ProgramEnvironmental Geoscience Potential impacts of oil and gas development on non-saline aquifers, Fox Creek
Released2019 12 01
AbstractWe investigated the aftershock decay rate of the two largest injection-induced earthquakes (IIEs) ever recorded in northeast British Columbia that occurred on August 17, 2015 (MW (moment magnitude) 4.6, ML (local magnitude) 4.9) and November 30, 2018 (MW 4.5, ML 4.7). These earthquakes are temporally and spatially correlated with hydraulic fracturing (HF) operations in the region. To conduct this study, we prepared a dataset of 134 aftershocks for the first sequence (Mahani et al., 2017) and 112 aftershocks for the second sequence (Visser et al., 2019). Their magnitude range is mainly between 1.0 and 3.0 and most of the events occurred at very shallow depths. We analyze the first two weeks of the two aftershock sequences to better characterize the significant decay of seismicity with time. Our analysis indicates that the aftershock decay rate of the 2015 (MW 4.6) earthquake sequence is characterized by a p value of 1.24. The seismicity decay rate is much faster for the 2018 (MW 4.5) sequence with a p value of 2.68. Overall, we find that the decay rate of aftershock activity of large IIEs and tectonic earthquakes similarly obey the modified Omori law with different p values. After termination of injection, our observed aftershock decay rate is approximated by the modified Omori law with an increased p value (p > 2), similar to the case of seismicity decay rate for stable pre-existing fractures in reservoirs (Langenbruch & Shapiro, 2010). In the presence of limited injection operations in a different geological setting, we observed a lower p value. Therefore, we speculate that geomechanical characteristics of pre-existing fractures and the operational parameters of nearby injection operations may be the main factors controlling the range of p value and consequently the seismicity rate of aftershocks.
Summary(Plain Language Summary, not published)
We study how the number of aftershocks decreases with time for the two largest induced earthquake sequences in northeast British Columbia that occurred on 17 August 2015 and 30 November 2018. Our results indicate that the decay rate of the 2018 sequence is much faster than that of the 2015 sequence. We speculate that the distribution of pre-existing fractures in the rock formation and different injection operations may be the main factors controlling the seismicity rate.

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