The nature and determination of stress in the accessible lithosphere

Results of stress determination show that stress state is characteristically heterogeneous and apparently unpredictable. Characterization of in situ stress state requires the determination of stress at individual locations and then spatial if not also temporal extrapolation. A variety of different measurements are used as a basis to determine stress state. Thus an adequate understanding of both the nature and origin of rock stress is essential. Representation of the lithosphere as a non-equilibrium, dissipative, dynamical system is shown to be consistent with observations of stress state and fluctuation of crustal displacement. The evolution of rock cores subject to a variety of perturbations in the laboratory can similarly be shown to be consistent with the evolution of a dissipative, dynamical system, driven in part by stored strain energy. These observations are inconsistent with the assumption that rock stress can be adequately represented by superposed traction and internally balanced stresses arising from quasi-static processes. The potential value of analyses of the dynamics of rock stress evolution is emphasized as a means to simplify the apparent complexity arising from present perceptions.