2D nonlinear gravimetric inversion to estimate basement relief and lateral variation of density contrast

Abstract

This study proposes using a two-dimensional nonlinear gravimetric inversion methodology based on the regularized Quasi-Newton method to infer the geometry of the boundary between the sedimentary deposit and its basement and to define the simulated lateral density contrast in a sedimentary basin environment. The interpretation model consists of a set of rectangular prisms in 2D space. The parameters estimated in this inversion proposal are the thickness of each prism and its density contrast, interpreted in terms of the depth of the basement and the lateral variation of contrast between the basement and the basin sediment. While most commonly used inversion programs neglect lateral density contrast to estimate basement depth, resulting in algorithms that overlooks much of the lateral geological complexity present in the subsurface, the proposal of this work encompasses such complexities more generically. In this research, the initial analysis involved tests with gravimetric anomalies generated by two synthetic models that exhibited variations in basement depth and lateral density contrast. Subsequently, the methodology developed was applied to data from the high-resolution Earth gravity field model, SGG-UGM-2, along a profile crossing the central part of the Tucano Basin, Bahia, Brazil.