AEM Cross-Gradient Constrained Inversion of Gravity and Magnetic Data

Abstract

Nowadays magnetics, electromagnetics and gravity are among the most abundant airborne surveys. Traditionally they aim at specific depth targets. For instance, Airborne Electromagnetic (AEM) data are known to provide reliable models of a few hundred meters deep; whereas, gravity and magnetic data can reveal geological features below few thousand meters depth. This depth-resolution difference has historically limited the combined interpretation of these data. We, however, hypothesize that there is a commonly sensed depth interval, which could be used to harness the joint inversion of the data and increase the reliability of the models in the wider depth extent. To demonstrate this we designed three inversion experiments using potential and AEM field data acquired in Western Australia. Firstly, we inverted each data set separately using a conventional 2D inversion strategy. Secondly, we jointly inverted the gravity and magnetic data using the cross-gradient constraint. Thirdly, we added a preliminary AEM resistivity model as a cross-gradient constraint for the 2D cross-gradient joint inversion of the gravity and magnetic datasets. Our results show that the three data sets sense a common area of the subsurface and that the vertical resolution of each data set influences in the shallow and deep structures of the joint models.