Fig. 2. Evolution of the fault damage zone as a function of increasing displacement on the fault (cf. Gudmundsson, 2011, Rock Fractures in Geological Processes, cited). The damage zone becomes gradually thicker. If the damage zone mechanical properties vary linearly with distance from the core, the variation in Young’s modulus may be as shown here. More commonly, however, the damage zone forms subzones with, commonly widely, different Young’s moduli (Fig. 3).