Folding and faulting in coulomb materials
Sand in laboratory scale analogue models of folding and faulting is usually assumed to behave as a simple Coulomb material in which failure occurs along planes inclined at an angle completely determined by the internal angle of friction. This simple model has inspired use of the inclined simple shear model to explain analogue model behaviour. Unfortunately the inclined simple shear model is incapable of describing the full richness of behaviour in sand-based analogue models since it cannot cope with rotations and it cannot satisfy general boundary conditions. A rotational simple shear description is developed in this paper which overcomes these obstacles. It is shown that this description explains high-angle back thrusts in contractional models, that it quantitatively predicts fault throws in listric-fault extensional models and that it provides a complete kinematic description for domino-fault block models including the transition from uniform stretch at the model base to rigid rotation in the model upper half.