This master's thesis seeks to ascertain if the vertical seasonal variations observed at permanent GPS stations (PGS) can be attributed to mass load deformations. The study focuses on seven PGSs in or around a highland region in south Norway. The mass loads examined include hydrological loads in the region and those related to water level fluctuations in nearby reservoirs. The study compares and corrects the vertical positions of a PGS against modelled vertical deformation resulting from mass displacement. Common mode filtering is employed on the GPS time series to minimise network errors. The findings reveal no direct connection between vertical displacements and the modelled hydrological mass load, as they exhibit phase shifts. Adjusting the observed PGSs' time series for the local effect and implementing a common mode filtering will significantly diminish the seasonal signal, although not entirely. This implies that either an unmodelled deformation signal influences certain PGSs in the study area or that these PGSs are subject to a similar error. Additionally, the study demonstrates that nearby water reservoirs contribute to the seasonal variation to a limited extent and do not cause substantial deformation at an adjacent PGS, particularly in comparison with other hydrological deformations
