MÉTODO DE ANÁLISE DE AMBIGUIDADE DA DIREÇÃO DE MAGNETIZAÇÃO REMANENTE E DA RAZÃO DE KOENIGSBERGER EM CORPOS GEOLÓGICOS 3D MAGNETIZADOS UNIFORMEMENTE

Abstract

We developed a new ambiguity analysis method for appraisal the remanent-magnetization direction and the Koenigsberger ratio (Q) of a uniformly magnetized source. Our method is grounded on a new formulation of the unit vector of the total magnetization direction which is described as the weighted sum of the unit vectors of the induced and remanent magnetization directions. The unit vectors of the induced and remanent magnetization directions are weighted, respectively, by λ, which we defined as the ratio between the induced and total magnetization intensities, and by the multiplication of λ by the Koenigsberger ratio Q. Using this formulation, we obtained analytical estimators for Q and the remanent magnetic inclination IR and declination DR. By assuming neither knowledge of the total magnetization direction nor particular interpretation model, we estimated the total magnetic inclination IT and declination DT via the equivalent-layer technique constrained by an all-positive magnetic-moment distribution. From this magnetic-moment distribution estimate, we performed a systematic search for both IT and DT to obtain a discrete data-residual map on the plane IT × DT. The ambiguity analysis consists in using the estimated and the picked IT and DT from the data-residual map considering prespecified errors, to calculate, using the analytical estimators, a family of curves of IR × Q, DR × Q, and λ × Q. These curves are quickly built up because we inverted the data only once. Tests with synthetic data illustrated a broader perspective of the relationships between the direction of remanent magnetization and the ratio Q. We also provide examples by applying this ambiguity analysis to total-field anomalies observed in various locations across Brazil, demonstrating both its effectiveness and limitations.