Fig. 7

The Bremgarten profile. a Bouguer anomalies and regional trend of the gravity field along the profile. The blue dots represent the stations where gravity data was collected for this study. The blue line highlights the main anomaly, while the green and orange broken lines indicate the side anomalies. See Additional file 4: Figure D.3.1 for location of stations, Additional file 1: Appendix A for gravity data and Additional file 2: Appendix B for information on the drillings. b Final model for the Bremgarten profile, made with a total of 7 prisms with a density contrast of − 500 kg/m³ for the uppermost three prisms and − 350 kg/m³ for the rest of the prisms (see also Fig. 5). The blue dots represent the observed residual anomaly (the dot size corresponds to the average uncertainty of ± 0.04 mGal), and the orange dots are the modelled residual anomaly values for model 10. The black bars indicate our maximum uncertainty of ± 0.13 mGal. The light blue line highlights the main anomaly. The effect of the side anomalies was modelled, and the results were subtracted from the residual anomalies. c Elevation (SwissAlti3D 2 m DEM (© swisstopo)) along the profile (blue solid line). The red broken line illustrates the bedrock topography of the model by Reber and Schlunegger (2016). The blue dots mark the locations of the gravity stations, the red diamonds indicate drillings that reached the bedrock. The black rectangles show the cross sections of the 7 prisms used for modelling. The red star is the projected location of the Forsthaus drilling (see Additional file 4: Figure D.3.1 for location), though it is quite far off the profile (c. 500 m, see Additional file 4: Figure D.3.1). Figure 7c also shows the intersections of the prisms with the profile that were used to correct the gravity residual anomaly for the side topography effects. This was done using a density contrast of − 650 kg/m³ (see Fig. 4 for explanation)