An improved search for magnetization direction

Abstract

Magnetic field interpretation is often conducted on an incorrect assumption that remanent magnetization is insignificant and that the resultant magnetization direction is in the local geomagnetic field direction. For compact anomalies various methods exist to test this hypothesis and return estimates of magnetization direction utilising trial reduction to pole (RTP) transforms. We have developed an analysis to return the magnetization direction which generates the most symmetric RTE anomaly and have shown that this approximately also matches input magnetizations of synthetic compact anomalies. Estimation of magnetization direction from elongate anomalies is more problematic and intrinsically less reliable, but nevertheless we found that we were able to recover approximate magnetization direction from these anomalies using cross-correlation of an analytic signal function computed from vertically integrated gradients (which we term the ?total vertically integrated gradient? or TVIG) with RTP and RTE grids computed for trial magnetization directions. The various methods are readily and automatically obtained from scanning TMI grids. The resulting magnetization direction estimates are empirical rather than analytic and are approximate. They are best used as initial estimates prior to application of more rigorous, manual methods.