Disclosed is a method of calculating critical area based on both independent and dependent compound fault mechanisms. This critical area is calculated by generating, for each simple fault mechanism in the compound fault mechanism, a map made up of polygonal regions, where values on a third dimensional z-axis represent the critical defect size for each single fault mechanism at a point x,y. These maps are overlaid and the planar faces (i.e., top surfaces) of each region of each map are projected onto the x,y plane in order to identify intersecting sub-regions. The dominant fault mechanism within each sub-region is identified based on an answer to predetermined Boolean expression and the critical areas for all of the sub-regions are accumulated in order to obtain the total critical area for the compound fault mechanism.