ABSTRACT
For years, geology has used deformation to determine the present and past tectonic stresses. This analysis is done on various scales: by observing fold geometry and mapping faults in the field, and by studying the deformation of the elements that make up the rocks. Many rocks belong to a transition category called elasto-plastic, often involving an elastic section at the center of the function, surrounded by two plastic extremities. Rocks with constituents that have a preferred direction in the rock matrix are common, particularly among sedimentary and metamorphic rocks. These anisotropy directions are planes of mechanical weakness. The shear strength of preexisting rupture surfaces in rocks has been well studied. In fact, tests on rock cores are not generally representative of a rock massif that contains a whole series of discontinuities or joints: the strength properties in rock samples are often clearly higher than those of the entire rock body.
