Calculating detachment depth and dip angle in sedimentary wedges using the area–depth graph

Abstract: We apply the area–depth–strain method (ADS) to predict the depth and the dip angle for an underlying bedding-parallel detachment in sedimentary wedge structures with stratigraphic wedge strata using an area–depth graph. An area–depth relationship is proposed and simplified to a linear relationship with depth as a function of excess area. This proposed ADS method gives the depth and dip angle of the detachment at any location in sedimentary wedges. The method does not yield the shortening magnitude from the area-depth graph because the area-depth relationship is different for this structural example from the established methods. We test the method by predicting the detachment depth and dip angle of two natural wedge structures that are well constrained: the Niger Delta fold-and-thrust belt, which has a single detachment, and the Cascadia detachment fold, which has multiple detachments. The predicted geometric values are generally consistent with the geometric characteristics of the two systems. The ADS method is a powerful method for constructing subsurface structural geometries using well constrained near-surface geometry for decollement sedimentary wedges, and is independent of bed-length, bed-thickness and regional horizon throws.