Numerical investigation of parameters influencing back-thrust development in outer wedge fronts of fold-and-thrust belt systems

Thrusting in fold-and-thrust belts can manifest in different styles. Here we investigate the parameters influencing back-thrust development over fore-thrust development at the frontal part of fold-and-thrust belts using numerical geomechanical forward modeling. We vary the strength of the material involved, the dip and friction of the décollement, and the displacing boundary conditions to examine the impact of these properties on back-thrust development. The results of this numerical sensitivity analysis reveal that back-thrusting mainly increases with increasing material strength and decreasing friction coefficient of the décollement. Décollement dip has a less prominent impact on back-thrusting, but decreasing the décollement’s dip angle enhances back-thrusting likelihood. In summary, we find that the contrast between the work necessary to shear the wedge material and the work necessary to slide along the décollement is the main driver for initiating back-thrusting (high contrast) over fore-thrusting (low or even negative contrast), which compares well with field observations. In addition, we also investigate and discuss the effect of a pure lateral displacement rate boundary condition vs. a condition in which displacement along the décollement is coupled with the lateral displacement rate on numerical simulations of back-thrusting development.