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TitleStress chatter via fluid flow and fault slip in a hydraulic fracturing-induced earthquake sequence in the Montney formation, British Columbia
AuthorPena-Castro, A F; Roth, M P; Verdecchia,; Onwuemeka, J; Liu, Y; Harrington, R M; Zhang, Y; Kao, HORCID logo
SourceGeophysical Research Letters vol. 47, issue 14, e2020GL087254, 2020 p. 1-12,
Alt SeriesNatural Resources Canada, Contribution Series 20200100
PublisherBlackwell Publishing Ltd.
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia; Alberta
Lat/Long WENS-126.0000 -115.0000 59.0000 52.8333
SubjectsScience and Technology; hydraulic fracturing; faults; earthquakes; earthquake studies; Montney Formation
Illustrationsdiagrams; graphs; location maps
ProgramEnvironmental Geoscience Shale Gas - induced seismicity
Released2020 07 08
AbstractSource 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 two days following injection 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 sub-vertical surfaces in a ~ 1 km wide deformation zone. Aftershock distribution is consistent with static stress triggering from the Mw 4.2 coseismic slip. Our analysis suggests complex hydraulic and stress transfer between fracture networks needs to be considered in induced seismic hazard assessment.
Summary(Plain Language Summary, not published)
In this study, we integrate local seismic monitoring and numerical modeling for a moderate-sized hydraulic fracturing (HF) induced earthquake sequence in northeast British Columbia, Canada, to reveal a two-step stress transfer process. A nascent, near-vertical fracture network in the sedimentary layers likely developed in the fault growth and basin infill of the Dawson Creek Graben Complex and hydraulically channeled injected fluids to a thrust fault in the basement, leading to a rapidly increased fluid pressure that initiated the mainshock rupture. Static stress change from the main event subsequently triggered the aftershocks within the overlying sedimentary sequences. Our results also suggest the relative injection volumes and/or wellbore pressures required to create HF at each stage of neighboring wells may be diagnostic of the presence of hydraulic connectivity to the basement, which tends to promote large magnitudes events.

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