A user guided expert system approach to 3D interpretation of magnetic anomalies

Abstract

Research into the development of an expert computer system for 3D magnetic modelling has yielded a methodology that can be applied to a wide range of magnetic exploration problems. The research focussed on the development of a semi-automated method for realistic 3D modelling of magnetic units truncated by an unconformity. Using the models produced by this process it is possible to map depth variations at the unconformity surface, map irregular geological boundaries of magnetic units and estimate magnetic susceptibility values. The objective of the research was the development of an interactive tool that would allow an interpreter to select a magnetic anomaly with a mouse and have the expert system produce a complete 3D model of the magnetic source distribution. In addition, the interpreter is required to select a geological constraint that biases the model creation in a geologically plausible manner. The research required the development of an expert system that emulates the procedures used by an experienced interpreter and an inversion methodology that could resolve complex 3D objects with fuzzy geological constraints. The system had to be suitable for inclusion in popular mapping systems. For appropriate anomalies, this process replaces innumerable individual steps that are normally required to manually construct a complex 3D magnetic model. As a result it is possible to replace a lengthy manual process that may take hours with one that can take less than a minute on a desktop PC.