Evolution of the surface deformation profile and subsurface distortion zone during reverse faulting through overburden sand

Abstract

The 2D distinct element method was used to investigate the propagation of fault rupture traces through overlying sand during reverse faulting along a range of dip angles and at different vertical throws. Calibrated micromechanical material parameters were used in the numerical simulations, which were validated through a comparison of the simulation results with those obtained from a centrifuge experiment involving acceleration at 80g. The Gompertz sigmoid function with three parameters provided the best fit to the normalized surface deformation profiles obtained both from the numerical simulation and from centrifuge experiments. The three parameters that characterized the Gompertz sigmoid function were the normalized scarp height, the maximum slope on the scarp, and the location of the reverse fault outcropping. A surface deformation profile slope of 1/150 was used as the setback criterion. The normalized affected width and fault outcrop relative to the fault tip were determined for reverse faults having a variety of dips and throws. The dip angle significantly affected the kinematic mechanism underlying reverse faulting. At a given vertical throw, the scarp height increased as the dip angle decreased in the cases of α<45°, and the scarp maintained a relatively constant height in the cases of α>45°. As the dip angle decreased, the location of the fault outcropping shifted toward the footwall and the maximum slope on the scarp increased. The horizontal displacement played a significant role at low dip thrusts (α=22.5°, 30°, 37.5°), a back-thrust fault developed, and an inverted triangle wedge formed in the subsurface.