Stress Chatter via Fluid Flow and Fault Slip in a Hydraulic Fracturing-Induced Earthquake Sequence in the Montney Formation, British Columbia

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 M(w)4.2 (M(L)4.5) hydraulic fracturing-induced earthquake sequence. The isolated occurrence of the mainshock at a depth of similar to 4.5 km in the crystalline basement 2 days following injection onset at similar to 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 similar to 1 km wide deformation zone. Aftershock distribution is consistent with static stress triggering from the M(w)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.