The relation between a macro constitutive law of friction during faulting with specified local or micro laws is assessed by means of numerical simulation. A 3-D numerical model based on the Discrete Element Method was used to simulate the rupture of a fault, in which each local grid point on the fault is assumed to follow the micro friction law. Then, the macro friction model is estimated by averaging, on a selected area, relevant variables monitored during rupture. After considering a homogeneous material, the influence of non-homogeneity was evaluated by assuming that mass density, Young's modulus and friction coefficient were correlated Gaussian random fields. In both cases, only minor variations in the parameters of the macro constitutive law in relation to the micro constitutive law were perceived. However, the presence of indentations on the fault was found to affect the macro constitutive law. Copyright 2006 by the American Geophysical Union.