Confidence in geological interpretation : a methodology for evaluating uncertainty in common two and three-dimensional representations of subsurface geology

The Lake District DGSM project (Clarke, 2004) represented a first attempt by the British Geological Survey to construct a three-dimensional model from two-dimensional, and often poorly constrained, subsurface interpretations. Over the course of this project it became clear that success depended on objective evaluations of confidence in the input interpretations in order to resolve the inevitable conflicts between them. Confidence in modelling has been considered by other BGS workers (Cave & Wood, 2002) but they have concentrated on uncertainty in the aspects of numerical modelling. Assessment of the uncertainty in the geological aspects of interpretations has not been considered. This report describes a method of evaluating confidence in the geological aspects of twodimensional interpretations of the subsurface that was developed out of necessity to resolve problems in the Lake District DGSM. This report gives a generic overview of the method but uses examples taken from the Lake District DGSM to demonstrate it. The method is primarily aimed at evaluating confidence in standard two-dimensional representations of surface and subsurface geology (maps, cross-sections, contoured horizon plans etc.) so that their value to three-dimensional modelling can be assessed. However, the technique can be taken further to evaluate confidence in three-dimensional models and a method for doing so is described. The assessment method is still in the embryonic stages of development. To date it has been applied to the Lake District DGSM with success and is currently being used to resolve similar problems in the Glen Lochy DGSM. However, with the exception of these projects it remains largely untested.