Modelling of sedimentary basins from gravity anomalies with variable density contrast

Summary. The decrease of density contrast with depth in sedimentary basins could be approximated by a quadratic function. The sedimentary basin is viewed as a number of outcropping vertical prisms put in juxtaposition at each observation point. Equations are derived for the gravity anomaly of a vertical prism for a quadratic density function. The initial model is obtained by calculating the thicknesses of the prisms at each station by an infinite slab formula. The differences between the observed anomalies and the anomalies of the initial model at each station are used to modify the initial model. A computer program is developed for initial estimates and refinement of the model. The method is applied to interpret the gravity anomaly of San Jacinto Graben, California, where sediments filling the graben have a density contrast that can be approximated to a quadratic function. Finally the convergence of the method is discussed.