Multiscale edge analysis of potential field data

Abstract

Mapping the three-dimensional distribution of rock properties from potential field data is a difficult and arduous task, with inherent ambiguity remaining a major problem. We apply a combination of automated interpretation procedures, based on multiscale wavelet analysis and three-dimensional visualisation methods, in an attempt to extract geometrical information from potential field datasets, and display this information in an easily understandable and intuitive way. The resulting visualisations are similar to 'worm' maps commonly produced by interpretation of aeromagnetic data, but are defined in three dimensions. The techniques are tested on a series of synthetic and observed datasets, of varying complexity and geographical scale. The tests show both the effectiveness of the technique as an aid to the geological interpretation of potential field maps and in its use for providing constraints on the three-dimensional geology. The results of the testing on synthetic datasets show that for certain geometries there is an intuitive relationship between 3D edge location and shape, and subsurface geometries. Such relationships prove particularly robust even under 'noisy' conditions where surface features (e.g. the response of laterites in magnetic datasets) mask the coarser scale features that characterise the broader geological picture. Three real datasets at different geographical scales have been analysed. These include the Western Australian gravity dataset (representing the continent-scale), aeromagnetic data covering a 1:100,000 scale map sheet from central Victoria (representing the district-scale), and a prospect-scale aeromagnetic dataset from a mineralised greenstone terrane in Western Australia. The results produce different information at the different scales. At the continent-scale the multiscale edges allow discrimination of different tectonic styles, and comparison of the significance of crustal-scale structures. At the district- to prospect-scale, the edges can be used for geological mapping purposes such as to map subtle changes in sedimentary sequences, map alteration patterns, and constrain pluton geometries at depth.