A WORK MINIMIZATION ANALYSIS OF THE EVOLUTION OF FAULT STRUCTURES WITHIN ACCRETIONARY WEDGES

We propose that fault systems evolve following the principle of work minimization. The total work within a deforming fault system is the sum of work against gravity, internal work, frictional heating, seismic radiated energy and work of generating new fault surfaces. Numerical models of sandbox wedges have shown that the transition from underthrusting to accretion follows the principle of work minimization. Our results show that the total work done by the contracting wedge increases during the underthrusting stage up to a critical value when the propagation of a new frontal thrust significantly reduces the work required for further deformation. The numerical models of sandboxes also predict energetically most viable position and vergence for the nucleation of a new thrust. The shear localization producing a new thrust ramp will occur where the energy spent by the deforming wedge is minimized due to an optimal combination of gravitational, frictional, internal and propagation work terms. This numerical methodology is applied to natural accretionary systems, such as at the Nankai trough, to show the distribution of work within these systems. Furthermore, we explore the conditions that favor active forethrust versus backthrust development.