Strain energy density and Navier-Coulomb stress are measures for propensity of fault surface generation within a given rock volume. Plots of strain energy density and Navier-Coulomb stress are used to predict where a new fault is more likely to nucleate. We calculated where a new forethrust will be located at the toe of a thrust wedge (highlighted by the dashed line) developed in non-cohesive sandbox models and whether forethrusts, more commonly observed than backthrusts in real accretionary complexes, are energetically more efficient. Model results also suggest that the new thrust ramp nucleation does not evolve bottom-up from the basal detachment, but within the layer, propagating both fault tips toward upper and lower bedding plane detachments. Figure 11 from Del Castello and Cooke (Underthrusting-accretion cycle: Work budget as revealed by the boundary element method, J. Geophys. Res., 112, B12404, doi:10.1029/2007JB004997, 2007).
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