Variation in geometries and displacement along thrust faults: a quantitative analysis from sandbox models

The present work combines theoretical analysis, laboratory experiments, and field examples together with quantitative analysis to understand displacement variation along fault surfaces with varying dip angle. Two sandbox experiments are described to quantitatively analyze the interactions between shortening and sedimentation during late stages of deformation. The two models consisted of sand layers with single and two microbeads layer/s within the sandpack, sieved over horizontal frictional detachment. The models demonstrate that the overlying sediment load bears a major role on kinematic of developing structures. Fault displacement varied along imbricate thrusts due to variation in fault dip angle in the listric geometry. Maximum displacement occurred in the up-dip direction (up-section or near fault tip) along the faults where fault dip angles were shallower and favourable for thrust displacement. In contrast, the displacement was limited in the down-dip direction (down-section or near basal detachment) where fault dip angles were steeper. The variation in fault displacement with fault dip along the fault surfaces made it possible to establish an inverse relationship between the fault dip and related displacement values, i.e. lower is the dip angle, greater the displacement and vice versa. Despite the inherent limitations and assumptions of laboratory experiments, application of results to natural examples sheds new light on the mechanics and geometry of thrust faults from the deep to shallow structural levels as well as structural patterns that could appear as anomalous at a first sight.