Indication of the uplift of the Ardenne in long-term gravity variations in Membach (Belgium)

We report on the results of 7 yr of collocated gravity observations made with an FG5 abso- lute (AG) gravimeter and a GWR C-Series superconducting gravimeter (SG) located at the Membach Geophysical Station in eastern Belgium. The SG gravity residuals track changes in gravity periodically observed by the AG, at the microgal level. Further, in the SG resid- ual signal we distinguish a quasi-seasonal term that can be mostly explained by variations in local water storage effects. In the AG time-series we observe a small trend in the gravity of −0.6 ± 0.1 μGal yr−1 perhaps indicating that the Membach Station is being displaced up- wards by about 3.0 mm yr−1. An uplift of the region is confirmed by Global Positioning System (GPS) measurements performed 3 km away. We are able to explain the features in the gravity time-series in terms of water storage variability, post-glacial rebound and tectonic activity.