Fig. 2

A topographic view of the study area showing the location of the newly acquired 80 gravity points (red triangles) and the compiled tunnel gravity data points (77 points, blue circles). The green triangles represent our newly established relative reference points, which we tied to existing gravity reference points (magenta hexagons) and used to open and close daily measurement loops during the campaigns. The cyan dashed line represents the 2D model reference line, onto which both the geological model units and the gravity measurements are projected for comparison between synthetics and observations using 2D forward modelling. The background colours represent the mapped geological unit geometries at the surface; the geological units are simplified from and freely accessible at https://map.geo.admin.ch/. The inset in the lower left corner indicates the location of the study area (red box) in Switzerland in topographic view