Interactive optimisation of 3-D subsurface models using potential fields

Modern workflows for construction of 3-D data-constrained Earth’s subsurface models in complex geological environments require sophisticated research software tools capable of handling interdisciplinary data and analysis in both visual and quantitative context. Integration of potential field data – gravity and magnetics – into the model building process is a key component that helps to bridge the gaps in the sparse input data by fitting the modelled response to the measurements. On the basis of IGMAS+ – a free cross-platform potential field modelling software – we show how 3-D model building can be complemented by interactive optimisation (inversion) of the triangulated subsurface model geometry. The optimisation is done by means of Covariance-Matrix-Adaptation Evolution Strategy (CMAES) which proved to be efficient for strongly non-linear problems with high-dimensional parameter space. In order to avoid topology distortions of the triangulated model domain, we use a concept of warping the space containing a model, rather than operating on the model vertices. The space warping implies an elegant solution using a system of virtual elastic springs connecting the lattice nodes. The optimisation workflow is demonstrated on synthetic and real case studies. We also show how an interpreter can interact with the process: visually control and influence the quality of the optimisation on a timeline. The proposed workflow is an efficient tool for automated quick model construction, validation and rebuilding, as well as for testing of multiple modelling hypotheses.