Human interaction in geophysical inversion

Abstract

Numerical inversion of geophysical data does not normally require user interaction apart from the selection of initial inversion parameters. However, such an inversion often returns a single solution based upon default parameters. While this solution will be geophysically correct, assuming convergence of the algorithm, it may not be the most geologically reasonable answer. It is necessary to incorporate human interaction in selecting inversion solutions. We do this through an automatic system that provides a user-directed search of the space of geophysical solutions. Rankings assigned to numerical inversion results guide a genetic algorithm in advancing towards a conceptual target. Our example uses resistivity and chargeability data from a pole-dipole induced polarisation survey collected during a mineral exploration program. We invert for specific geological features: steeply dipping conductive and/or chargeable bodies below a weathered near-surface layer, separation of chargeability targets in a spatial sense, and greatest depth of resolution of the inversion algorithm. The interactive system is an organised way to investigate the solution space for results that emphasise these geological possibilities.