Fig. 4
From: Overdeepenings in the Swiss plateau: U-shaped geometries underlain by inner gorges
Example of how the residual anomalies were determined, using the Bümpliz profile as an example. a The target overdeepening with a Quaternary fill occurs beneath a generally flat surface. It is flanked by a surface topography on either side, which is underlain by Molasse bedrock on the SSE margin, and by a glacial till on the NNW side. b We determined the regional gravity gradient using the measured gravity values (blue dots, where the size of a dot corresponds to an estimated average error of ±0.04 mGal while the maximum uncertainty of ±0.13 mGal is shown by error bars, see text) on the lateral boundaries of our target overdeepening. c The residual gravity anomalies are determined through calculating the difference between the regional gravity gradient and the measured Bouguer anomalies. Because the Bouguer anomalies were calculated with a standard density of 2670 kg/m3, a positive surface topography made up of Molasse bedrock with a density of 2500 kg/m3 will yield negative residual anomaly values. Such a signal would disappear if a correction with a density difference of − 170 kg/m3 would be applied (difference between the standard Bouguer density of 2670 kg/m3 and that of the Molasse bedrock according to Bandou et al., 2022). On the NNW boundary, the positive topography underlain by Quaternary sediments with a density of 2000 kg/m3 also yields a negative residual anomaly signal, which could be removed if a correction with a density of − 670 kg/m3 would be applied (difference between the standard Bouguer density of 2670 kg/m3 and that of Quaternary sediments). If the overdeepening fill would be replaced by Molasse bedrock, then the residual gravity anomaly signals would also disappear. Accordingly the mass of the Quaternary fill causing the negative gravity anomaly signals can be estimated through modelling thereby using information about the density difference between the Molasse bedrock and the Quaternary fill