Analogue Sandbox Models of Thrust Wedges with Variable Basal Frictions

Scaled analogue sandbox models have been used to simulate the growth of Coulomb thrust wedges in isotropic cohesionless and anisotropic cohesionless materials. Variations in the basal coefficient of friction by using different materials as basal detachments, combination of basal detachments and the anisotropy of the layered system have been investigated. Imbricate fans of dominantly foreland-vergent thrust systems are developed in the way similar to those developed in accretionary prisms and in foreland fold and thrust belts. Critical-taper wedges close to theoretically predicted geometries are developed for intermediate values of basal friction (mb = 0.47), whereas for the lower value of basal friction (mb = 0.37), low-taper wedges are formed with slopes less than the theoretically predicted. Supra-critical wedges are formed when the high basal friction (mb = 0.55), is either equal to or greater than the coefficient of friction of the deforming material in the wedges. Then the wedges have a high taper angle close to the angle of rest for the modelling material. Similar geometries developed when the experiments were carried out on combination of two materials with basal frictions as: intermediate-low, low-intermediate and low-high. The spacing of thrust faults increases with increased basal friction. Higher basal friction or anisotropy within the layered systems favours displacement along foreland-vergent thrusts and eventually checks backward breaking thrusting.