NUMERICAL-SIMULATION OF FAULTS AND SHEAR ZONES

A numerical model is developed to simulate faults and shear zones in r ocks. It consists of a 2-D set of soft spheres in plane-strain compres sion tests. The soft spheres obey Newton's equations of motion and ini tially interact with viscoelastic forces. The fracturing process is si mulated by the transition from 'attractive-repulsive' forces to solely 'repulsive' forces. The behaviour of the solid is studied by varying two independent parameters: the density of pre-existing fractures and the confining pressure. The density of pre-existing fractures controls the intrinsic cohesion of the rock. A transition from brittle to duct ile behaviour is generated by letting this parameter vary. The deforma tion is localized along narrow shear zones when the solid is intact. A s the cohesion decreases, the deformation becomes more homogeneous. Th e effect of the confining pressure is then studied for different cohes ions. In loose media a variation of the stress drop in stress-strain c urves is observed.