  Earthquakes induced during hydraulic fracturing operations have occurred in a
number of locales. However, in-situ studies aimed to discern the triggering
mechanism remains exclusively statistical in their nature. Here, we calculate
the fault slip-tendencies of eleven hydraulic fracturing induced earthquakes in
a historically aseismic area using a recently constructed quantitative model
for in-situ stresses. It is shown that the ambient pore pressures of the nearby
Duvernay unconventional reservoirs can provide enough Pf triggering fault
movement. The local fluid pressures acting on the fault could readily be
increased above the critical value if a hydraulic connection exists between the
fault and a propagating hydraulic fracture. The critical pressures necessary to
induce slip, is estimated using a probabilistic model that incorporates
uncertainties of stress and fault mechanical properties. These critical
pressures are greater than expected hydrostatic pressure but less the pore
pressures of nearby unconventional reservoirs.
