THE BIFROST PROJECT - GPS DETERMINED 3-D DISPLACEMENT RATES IN FENNOSCANDIA FROM 800 DAYS OF CONTINUOUS OBSERVATIONS IN THE SWEPOS NETWORK

This presentation summarizes results obtained from 800 days of operati on of SWEPOS, the Swedish permanent GPS array. Located in the area of the Fennoscandian land uplift, SWEPOS is the main measuring device for the BIFROST project, aiming primarily at determination of crustal mot ions and changes in global sea level in conjunction with postglacial r ebound. As a future prospect the project will contribute to determine present-day changes in the oceanic water budget as well as strive for a more complete understanding of the viscoelastic structure of crust a nd mantle. We show solutions of site positions obtained from the daily processing of the GPS observations. We determine their variations in time, discerning them from plate or frame orientation, and discuss a n umber of perturbation effects. Among these the possibility of random w alk monument motion is considered. The feasibility of single-site solu tions rather than baseline pairs is demonstrated. On the basis of 800 days of operation of the permanent network, data analysis is able to c onfirm the general rebound pattern. Comparison with both modelling res ults and evidence from mareograph and precise levelling shows high rat es of vertical surface displacement from GPS measurements in the centr e of the Pleistocene glaciation region. We discuss the possibility of rate biases due to problems with the terrestrial reference frames. (C) 1998 Elsevier Science B.V. All rights reserved.