Some comments on the inversion of multi-scale edges to create geological structure

Abstract

By taking the formulae used to create the gravitational and magnetic response of a dipping contact, it is possible to derive formulae for the points of maximum slope on a corresponding gravity or magnetic profile. If then a series of multi-scale edge points are determined from some gravity or magnetic survey it should be possible to determine the physical properties of the body using some type of inversion routine. In order to resolve depth to the top of the body, thickness of the body, slope of the contact and lateral position of the body, four simultaneous equations are needed. The four equations arrive from various upward continued levels of data. Due to the relatively low number of solutions for the simultaneous equations a Monte-Carlo style of inversion is used. It is not possible to determine the density contrast (or magnetic susceptibility contrast) using this technique. Two-dimensional models of the Kalinjala and Karari Shear zones (in South Australia) are shown. The equivalence of direct forward modelling of a dipping contact is discussed and the authors conclude that despite this equivalence multi-scale edge detection has its uses, notably for locating subtle gravity and magnetic features, and detecting regional structural trends.