Analytic Signal vs. Reduction to Pole: Solutions for Low Magnetic Latitudes

Abstract

As mineral exploration activity shifts to regions at low magnetic latitudes, interpretation skills acquired at high latitudes become harder to apply, thus leading to under-utilisation of expensive magnetic survey data. Changes in anomaly shape, reduction in overall amplitude and changes in map textures make the ready interpretation of geology from magnetic data difficult. These problems are worst for magnetic inclinations within 20° of the equator. Reduction to pole (RTP) is the best theoretical solution because it removes the effect of induced magnetisation and strike while preserving dip information. But, in practice, the standard RTP transform is difficult to apply at very low latitudes and produces poor-quality maps dominated by declination-parallel artefacts. Additionally, the transform cannot completely reconstruct NS-trending anomalies. The 3D Analytic Signal is a function of magnetic gradients and is easy to compute at all latitudes. It is almost but not entirely independent of magnetisation direction. It can be computed easily and accurately for any ambient and source magnetisation. However, it lacks the resolution that derivative maps provide and lacks the dip (and therefore structural) and textural information that total magnetic intensity and RTP maps contain.