What if your inversion has no numerical target?

Abstract

We present a system for inverting geological models in cases where there are no established numerical criteria to act as inversion targets. The method of interactive evolutionary computation provides for the inclusion of qualitative geological expertise within a rigorous mathematical inversion scheme, by simply asking an expert user to visually evaluate a sequence of model outputs. The traditional numerical misfit is replaced by a human appraisal of misfit. A genetic algorithm provides optimal onvergence into the target parameter space, while optimising an ensemble of solutions, so that the non-uniqueness of the problem may be explored. In order to facilitate analysis of the results, we employ a visualisation technique known as self-organised mapping to represent the parameter space covered by the numerous model outputs. The result is a simple view of an otherwise complicated multi-dimensional problem. A user may infer much about the controlling parameters in the model through a few graphical displays of the data. The potential of this interactive inversion and visualisation technique is demonstrated when we invert a geodynamic model for a conceptual pattern of fault spacing during crustal extension. We also present an example where the interactive scheme is linked to a numerical inversion of induced polarisation data. In this case, we are exploring for the numerical inversion parameters which lead to a particular geological output.