The Lake District DGSM : an overview of the model and best practice guidelines

The Lake District Digital Geoscience Spatial Model (DGSM) represents a first attempt by the British Geological Survey to produce a three-dimensional geological model in an area of the United Kingdom where there are few directly observed measurements of the subsurface. Consequently, the model is based largely on two-dimensional interpretations of the subsurface and a thorough understanding of the geology of the area gained as a result of the complete resurvey at 1:10 000 scale of the region during the last twenty years. This report describes the construction of this model. Modelling of the subsurface using interpretation, inference and geological understanding introduces issues of positional confidence for modelled horizons that are different from those encountered when modelling with directly observed measurements of the subsurface. A methodology for evaluating confidence in geological interpretations (Clarke, 2004) is applied to the DGSM. The resulting three-dimensional, subsurface horizons are a ‘weighted best-fit’ to the available interpretations, based on confidence in the data and methods used to construct each interpretation. This confidence is propagated from source through to model to express confidence in the final, three-dimensional model. The structural geometry of the modelled subsurface horizons is compared with available measured surface data. Anomalies between modelled and measured structural geometries highlight the assumptions and implications of two-dimensional interpretative methods as well as with three-dimensional modelling using two-dimensional subsurface interpretations. Based on the experience of building the Lake District DGSM, a Best Practice is introduced for the construction of three-dimensional subsurface models in analogous, complexly faulted areas of the United Kingdom.