Microseismic monitoring is increasingly being used to assess in real time the effectiveness of hydraulic fracture treatments. Operators are interested in three key questions. (1) Where are the microseismic events occurring (what is the size of the microseismic cloud)? (2) What is the failure mechanism (are fractures opening, closing, or shearing)? (3) Why is failure occurring in specific locations but not others (why are fractures not always symmetric with respect to the injection well and what is the geomechanical behavior of the reservoir)? In particular, the last question is difficult to answer from the recorded seismicity alone because the geomechanical behavior depends on the in-situ stress field, the local rock properties (lithologies), and any existing areas of weakness including faults, fractures and joints (Grob and Van der Baan, 2011). Geomechanical modeling can thus play a key role in better understanding both brittle and ductile deformation inside a reservoir because of hydraulic fracturing and the resulting microseismicity.