Inferring geological structures using wavelet-based multiscale edge analysis and forward models

Abstract

A set of semi-automatic tools for analysis of potential field data has been developed. These tools use wavelet analysis to automatically detect gradients or edges in potential field data. The tools are normally applied to different levels of upward continuation, providing automatic detection of edges in the potential field data at different scales of resolution. We refer to these edges at different levels of upward continuation as "multiscale edges". Commonly, sharp contrasts evident in potential field data (edges or gradients) are assumed to result from sharp discontinuities or interfaces between contrasting rock materials such as faults, unconformities, or intrusive contacts. Because of the inherent non-uniqueness of potential field problems, there can be no certain or unambiguous differentiation between different possible source rock geometries without reference to a priori information such as independent geological data. In many cases the a priori information which is most readily available describes a geological "style" which consists of some form of idealised or simplified geometry or expected range/strength of contrasts in rock properties. The common assumption that geological units are sharply bounded by faults and other geological contacts suggests that irregularities in geophysical potential-field images correspond to irregularities in the sub-surface rocks, and this relationship has been the basis for many forward and inverse modelling systems (Jessell, 1999). In order to document the results of the new, semi­automatic edge detection techniques, these techniques have been applied to synthetic datasets (Jessell, 1981; Jessell & Valenta, 1996). Each synthetic dataset investigates an idealised source geometry (e.g. intrusions, faults, dykes) the expected potential field data, and the resulting multiscale edges. The resulting "atlas" of source geometries and multiscale edges aids the interpretation of real-world data. The new analysis techniques and the "atlas" of multiscale edges, have direct application to calculations of depth to source, dip directions, and contact relationships.