A new method to calculate the stress tensor associated with slip along a population of faults is derived here. The method incorporates two constraints: First, the stresses in the slip direction satisfy the Coulomb yield criterion, and second, the slip occurs in the direction of maximum shear stress along the fault. The computations provide the complete stress tensor (normalized by the vertical stress), and evaluation of the mean coefficient of friction and the mean cohesion of the faults during the time of faulting. The present method is applied to three field cases: Dixie Valley, Nevada, Wadi Neqarot, Israel, and Yuli microearthquakes, Taiwan. It is shown that the coefficieet of friction of the three cases varies between μ < 0.1 to μ = 0.8. Further, it is demonstrated that previous stress inversion methods implicitly assume zero friction along the faults.