Crustal deformations at permanent GPS sites in Denmark

Abstract

The National Survey and Cadastre (KMS) is responsible for the geodetic definition of the reference network in Denmark. Permanent GPS stations play an important role in the monitoring and maintenance of the geodetic network. During 1998 and 1999 KMS established three permanent GPS station in Denmark, SMID, SULD and BUDP. Using almost 4.5 years of continuous data from the Danish station and the Swedish station, ONSA, we analyse the daily GPS solution due to crustal deformation caused by glacial isostatic adjustment (GIA). Although, displacements due to GIA are only 1-3 mm/year at the Danish GPS sites, the current precision of positioning using GPS allows us to observe these effects. The modelled horizontal GIA velocities and the observed horizontal residuals obtained from GPS show almost the same direction for all station. However, the observed velocity residuals are larger than the modelled GIA velocities. Furthermore, the difference of the observed vertical velocity residual rate between ONSA and SMID, and between ONSA and SULD seems to agree with the expected rate according to the postglacial model by Milne. However, the vertical velocity rate of BUDP seems to disagree with the model. Moreover, the analysis presented here uses a relative short period of data. The error of the vertical velocities (including reference frame drift) is order of ±1.1 mm/yr.