A two-dimensional finite difference model of the effects of erosion on the evolution of pore pressure within a moving thrust sheet

Abstract

There is indirect for the existence of abnormal pore pressures in continental thrust belts. Workers have also shown through modeling studies that abnormal pore pressures are to be expected in tectonic wedges which have the physical properties and boundary conditions appropriate for both accretionary prisms and continental thrust belts. However, little is known about the origin and evolution of any abnormally high pore pressures. The purpose of this study was to compute the pore pressures in the frontal part of the foreland fold and thrust belt. A two-dimensional finite difference technique was used to investigate the sensitivity of excess pore pressure generation and dissipation to the variation of physical properties of a thrust sheet (e. permeability, and thrust velocity). Special attention was given to the effect of erosion on the evolution of pore pressure within a submerged thrust belt exhibiting stratigraphy typical of North American thrust belts. The results of this model predict that high excess pore pressures can be generated within a thrust belt by conditions which are thought to exist in continental thrust sheets. Excess pore pressures and X (the Hubbert and Rubey parameter) are most often highest directly beneath the toe of the thrust sheet, creatina conditions favorable for rock failure and new thrust formation. Permeability changes have the greatest influence over pore pressure evolution within a thrust belt especially when vertical pemeabilities are less than 10-17 M2. However, even low permeability rocks may not be effective in impeding massive fluid dissipation in the face of slow thrust motion. Erosion slightly increases excess pore pressure beneath the toe of the thrust, however, it also broadens the concentration of excess pore pressure and X beneath the toe of the thrust sheet, thus decreasing the probability of new faults forming in that area. The presence of an overlying body of water increases total pore pressure throughout the thrust sheet, but it does not significantly increase excess pore pressure.