FMSI: A fortran program for inverting fault/slickenside and earthquake focal mechanism data to obtain the regional stress tensor

Abstract

Program FMSI inverts observations of slip directions on fault planes of known orientation in order to determine the best-fitting four-parameter stress tensor, defined by three principal stress directions and R=(σ2 − σ1)/(σ3 − σ1), and the associated uncertainty. Special effort is applied to two important aspects of this analysis: how to define the best-fitting model, and how to identify it. The misfit between a fault observation and a stress model is defined as a rotation of the combined fault plane/slip vector that achieves an orientation for which the observed and predicted slip directions on the fault plane are aligned. The best model is the one that minimizes the sum of these values for all data. Many different misfit rotations are possible; program FMSI allows the user to select from among a number of possible measures of rotation misfit, differing in solution quality and computational efficiency. The optimum stress model and estimates of confidence limits are determined by a systematic search over ranges of one stress magnitude and three stress orientation parameters.