Strength of the lithosphere: constraints imposed by laboratory experiments

The concept of strength envelopes, developed in the 1970s, allowed quantitative predictions of the strength of the lithosphere based on experimentally determined constitutive equations. The importance of a regime of semibrittle behavior is now recognized. Based on data from rocks without added pore fluids, the transition from brittle deformation to semibrittle flow can be estimated as the point at which the brittle fracture strength equals the peak stress to cause sliding. Knowledge of the stability of sliding along faults and of the onset of localization during brittle fracture has improved considerably. Major questions concerning the strength of rocks remain. In particular, the effect of water on strength is critical to accurate predictions. -from Authors