Nonlinear Dynamics of Rock: Hysteretic Behavior

We discuss the dynamics of media with hysteretic stress-strain properties. First, experimental evidence of the hysteretic behavior of rock is presented. This evidence leads to a pattern of unifying behavior whose origin is within the bond system of the material, which includes small cracks, intergrain contacts and, the cement that holds the grains in place. Nonlinear response is evident over a large frequency interval (dc to several MHz at least), and it is significant from strains of plasticity down to the smallest measurable strains (order 10^-8-10^-9). Second, some models related to such a behavior are outlined. Finally, oscillations and waves in hysteretic media are discussed.