EFFECTS OF ROCK ANISOTROPY AND HETEROGENEITY ON STRESS DISTRIBUTIONS AT SELECTED SITES IN NORTH-AMERICA

Provinces of regionally consistent horizontal stress orientations pers ist throughout the upper crust, and these may contain local areas wher e horizontal stress (sigma(H) orientations seem to rotate relative to the regional stress orientations in a consistent manner. We suggest th at the concept of an inclusion with anisotropy and heterogeneity of me chanical properties may be useful to explain some cases of sigma(H) ro tations. sigma(H) rotations up to 50-degrees and magnitude changes of 40% could reasonably be expected, based on simulations. Patterns corre late well with crustal observations; rotation of sigma(H) orientation reaches 25-degrees to 58-degrees in the differente cases studied. We a lso model a strike-slip fault zone as a soft inclusion, showing reorie ntations of sigma(Hmax) which agree with observed rotations near the M urre Fault in the Jeanne d'Arc Basin, Canada. Results imply that under standing the behaviour of soft and stiff inclusions, or expanding and contracting thermal inclusions for that matter, can help explain a num ber of geophysical and geological phenomena related to stress patterns .