**7. Discussion and conclusions**

A numerical modeling study has been carried out to investigate the application of the distinct element technique to the simulation of fault slip and induced seismicity resulting from a hydraulic fracture treatment via a wellbore in the vicinity of a natural fault. The model was able to predict the occurrence of post-injection seismicity in response to diffusion of the injected fluids, in a system governed by fracture permeability, long after the hydraulic fracturing treatment is finished and shut-in is initiated.

In most areas, regional-scale faults should be easily identified during geological site charac‐ terization studies. Smaller-scale faults or those that are shallow dipping (i.e., that do not daylight on surface and therefore would not be detected through surface mapping) may be more difficult to locate *a priori*. Experience gained from monitoring hundreds of hydraulic fracturing treatments with downhole geophones has shown that the occurrence of seismic events induced by the treatments is greatly influenced by the injection volume used during the operation. Improved understanding of this condition will allow designers and operators to control the amount of injection during a hydraulic fracturing treatment to minimize fluid pressure diffusion and subsequent slip of a neighboring fault.

The simulations presented here show great potential in providing a deeper understanding of the effect of natural fracture systems and pressure diffusion of fracing fluids into a neighboring fault causing shear slip and induced seismicity after a hydraulic fracture treatment. Future work will include modeling of hydrofrac fluid diffusion into a fault in the vicinity of the hydrofrac treatment site in a three-dimensional model.
