Inversão por etapas de anomalias magnéticas bidimensionais

Abstract

This work presents a three step magnetic inversion procedure in which invariant quantities related to source parameters are sequentially inverted to provide i) cross-section of two-dimensional sources; ii) intensity of source magnetization, and iii) inclination of source magnetization. The first inverted quantity (called geometrical function) is obtained by rationing intensity gradient of total field anomaly and intensity of vector anomalous field. For homogenous sources, geometrical function depends only on source geometry thus allowing shape reconstruction by using arbitrary values for source magnetization. In the second step, source shape is fixed and magnetization intensity is estimated by fitting intensity gradient of total field anomaly, an invariant quantity with magnetization direction and equivalent to amplitude of the analytical signal. In the last step, source shape and magnetization intensity are fixed and magnetization inclination is determined by fitting magnetic anomaly. Besides furnishing shape and magnetization of homogeneous two-dimensional sources, this technique allows to check in some cases if causative sources are homogeneous. It is possible because geometrical function from inhomogeneous sources can be fitted by a homogeneous model but a model thus obtained does not fit the amplitude of analytical signal nor magnetic anomaly itself. This is a criterion that seems effective in recognizing strongly inhomogeneous sources. The proposed technique is tested with numerical experiments, and used to model a magnetic anomaly from intrusive basic rocks of Paraná Basin, Brazil.