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 basin, northeast British Columbia, and stress modeling to
examine the spatial and temporal evolution of the 30 November 2018 M 4.5
hydraulic fracturing induced earthquake sequence. The mainshock occurred
at ~ 4.5 km in the crystalline basement two days
following injection at ~ 2.5 km, suggesting direct
triggering by rapid fluid pressure increase via a high-permeability
conduit. Most of the aftershocks are located 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 also consistent with static stress triggering
from the M 4.5 coseismic slip. Our analysis suggests complex hydraulic
and stress transfer between fracture/fault networks needs to be
considered in induced seismic hazard assessment.