SHEAR-TYPE FRACTURE ORIENTATIONS AS AN INDICATOR OF THE PRINCIPAL STRESS AXES DIRECTION

Most of the existing stress field reconstruction methods involve fracture systems to determine the stress state in a small-volume geomedium. The principal stress axes orientations at a point can be reconstructed from a pair of conjugate fractures. Based on mathematical modeling of compression stress field in the shear zone, this article shows that even when only one of two conjugate fracture systems develops and another one does not or is not being formed at all, the shears of the existing system are formed at an angle to the local maximum compression axis. Therefore, when the compression failure point is in the linear part of the Mohr diagram, the formation of even one shear gives a lot of information concerning local principal stress axes orientations at the formation point. This information can be used under rather restricted conditions – with knowledge about the intermediate principal stress axis orientation and the considered-volume medium location at the moment of shear formation, but all this can be obtained, for example, in physical modeling. Successive formation of shears allows for accurate monitoring of the variations in principal axes orientations irrespective of whether the precise shear angle is known.

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