Stress changes related to the depletion of gas reservoirs in the northern Netherlands can lead to small seismic events. Field data analysis makes it very likely that these events are the result of reactivation of existing faults or joints in or near the reservoirs. DIANA is used to model 3D gas reservoirs, in order to analyse stress development and fault reactivation during gas depletion. The models described in this paper are 12,000 x 12,000 x 5000 m and consist of approximately 59,380 TE12L- and T18IF-elements. Calculation results are analysed in terms of relative shear displacements (RSD), stress paths and mobilised shear capacity (MSC). Newly developed and complex formulas for MSC are successfully applied by means of the ‘Results calculate expression.’-option in Femview. It shows the possibility of implementing very complicated formulas in Femview. Modelling of the subsurface is a data-limited problem. The presented quantification methods are used to choose appropriate values for strength and pore pressure development of the interface elements for modelling of the fault. An application example illustrates the use of the methods and is supported by field data and earlier research work.