The shallow and deep crustal structure in Zagros from inversion and forward modeling: insights from the application of Moho-free Bouguer anomaly

Abstract

The contribution of shallow and deep portions of crust in Bouguer anomaly is a long-lasting challenge. Several attempts including filtering of data are being performed. Filtering outcomes are enormously subject to disagreements due to disputable possible choice of cut-off wavelength. Here, we develop in novel strategy to divide the contribution of shallow and deep crustal structures in the Bouguer anomaly. The Moho relief is estimated by the inversion of Bouguer anomalies. The gravity effect of the volume mass between the estimated Moho and the ground surface is computed by parametrization of the volume mass by different meshes (tensor, quad tree, and octree). Octree mesh is opted as the best one after assessing the different meshing results visually and statistically. Then this gravity effect is subtracted from the Bouguer anomalies to obtain the Moho-free Bouguer anomalies. This Moho-free Bouguer anomaly is inverted to obtain the uppermost density contrast representing a proxy for sedimentary thickness and/or magmatic intrusions. The inversions are carried out by using a very popular and robust method for non-linear problems which is called sparse norm inversion and is accessible through SimPEG (Simulation and Parameter Estimation in Geophysics) in Python. Importantly, the inversion process does not need an initial geometry model or density contrast and is completely automatic.