A NEW METHOD FOR INTERPRETATION OF AEROMAGNETIC MAPS: PSEUDO‐GRAVIMETRIC ANOMALIES

Abstract

The purpose of this paper is to describe a method of interpretation based on a transformation of the total magnetic intensity anomalies into simpler anomalies. The result of this transformation is the elimination of the distortion due to the obliquity of the normal magnetic field, so that the resulting anomalies will be located on the vertical of the disturbing magnetized bodies. The starting point of the theory is the well known relation between magnetic potential V and Newtonian potential U—relation which can be written: [Formula: see text] with: [Formula: see text] = magnetization, f = 66.7×10−9 u ⋅CGS, σ = assumed density of magnetized bodies. This relation may be considered as a partial differential equation. The boundary condition consists in the measured values of the total field T(P ) known at each point P at the datum plane. As T(P) is the derivative of a harmonic function V, we can determine this function everywhere above the datum plane. Solving then the partial differential equation, we find the Newtonian potential U and its vertical derivatives g, g′, g″⋯. Finally, we obtain these quantities as functionals of the measured magnetic anomaly T(P). For instance, one of the formula is [Formula: see text] where H(M, P) is the kernel of the transformation allowing the direct computation of g(M)—an anomalous field which will be called “pseudo‐gravimetric anomaly.” Of course, the pseudo‐gravimetric anomaly has all the usual properties of a gravimetric anomaly. The field of g(M) presents no distortion and the interpretation becomes as easy as that of a Bouguer anomaly map. To perform the actual routine calculations of this transformation, we start with the values of T taken on a rectangular or trigonal grid, as for the usual computation of the vertical derivatives. The use of punched‐card equipment speeds up considerably these calculations.