Methods and uncertainty-estimations of 3D structural modelling in crystalline rocks: A case study
Abstract. Exhumed basement rocks are often dissected by faults, the latter controlling physical parameters such as rock strength, porosity, or permeability. Knowledge on the three dimensional (3D) geometry of the fault pattern and its continuation with depth is therefore of paramount importance for projects of applied geology (e.g. tunnelling, nuclear waste disposals) in crystalline bedrock. The central Aar massif (Central Switzerland) serves as study area, where we investigate the 3D geometry of the Alpine fault pattern by means of both surface (fieldwork and remote sensing) and underground ground (mapping of the Grimsel Test Site) information. The fault zone pattern consists of planar steep major faults (kilometre-scale) being interconnected with secondary relay faults (hectometre-scale). Starting with surface data, we present a workflow for structural 3D modelling of the primary faults based on a comparison of three extrapolation approaches based on: a) field data, b) Delaunay triangulation and c) a best fitting moment of inertia analysis. The quality of these surface-data-based-3D models is then tested with respect to the fit of the predictions with the underground appearance of faults. All three extrapolation approaches result in