INTEGRATED STRESS DETERMINATION BY JOINT INVERSION OF HYDRAULIC TESTSAND FOCAL MECHANISMS

An inversion method, based on a genetic algorithm, is proposed for int erpreting jointly various kinds of stress data in order to overcome th e limitation, in number and quality, of each data set. The method has been applied to results from hydraulic tests in boreholes and to focal mechanisms of induced seismicity observed within the same depth inter val. The regional stress field is described by two symmetrical tensors . The first one represents the stress at a given depth and the second one the vertical stress gradient. Results indicate that one of the pri ncipal directions is vertical. They are consistent with all but one of the hydraulic tests considered in the inversion and with about 70% of the focal mechanisms. This inversion confirms previous results sugges ting that, for the scale of these induced microseismic events, the reg ional stress field cannot be determined solely from an inversion of th e fault plane solutions.