A new gravity inversion method for multiple subhorizontal discontinuity interfaces and shallow basins

Abstract

We present a method for 3-D gravity inversion designed to obtain density contrast models described by subhorizontal layers limited by irregular discontinuity interfaces and models constituted by shallow basins with light infill. It is based on a previously published inversion method that provides, in a nearly automatic approach, the 3-D geometry of isolated anomalous bodies. The basic adjustment constraints are model fitness (fitting the anomaly data) and model smoothness (minimizing the total anomalous mass). For models corresponding to subhorizontal layers, we consider an additional minimization condition: the proximity to prescribed horizontal interfaces. This condition is arranged by including an additional weighting (inverse proportional to the distance to the interface) in the covariance matrix for model parameters. The approach works, according a growth process that increases, step by step, the volume of the adjusted anomalous bodies. Some advantages of the method are simultaneous adjustment of a (linear) regional gravity trend, possibility of including simultaneously positive and negative anomalous structures in the model, and unified inversion approach for isolated bodies, basins, and subhorizontal interface structures. We include several simulation examples and an application case (layered model for the volcanic island of Tenerife).