1. FORWARD AND INVERSE MODELLING OF GPS OBSERVATIONS FROM FENNOSCANDIA G.A. Milne 1, J.X. Mitrovica 2, H.-G. Scherneck 3, J.L. Davis 4, J.M. Johansson 3, H. Koivula 5, M. Vermeer 6 1 Dept. of Geological Sciences, University of Durham, UK 2 Dept. of Physics, University of Toronto, Canada 3 Onsala Space Observatory, Sweden 4 Harvard-Smithsonian Center for Astrophysics, USA 5 Finish Geodetic Institute, Finland 6 Institute of Geodesy, Helsinki University of Technology, Finland

2. BASELINE INFERENCES FOR FENNOSCANDIAN REBOUND OBSERVATIONS SEA LEVEL AND TECTONICS Apply GPS to observe the present-day deformation field in Fennoscandia. Employ observations to: (1) Infer GIA model parameters. (2) Estimate secular height shift of geoid. (3) Examine importance of neotectonic processes.

4. GIA MODEL Earth Forcing Earth Rheology Rotational potential Euler equations Surface loading Ice ICE-3G (Tushingham & Peltier, 1991) FENN+BARENTS (Lambeck et al., 1998) Ocean Sea-level equation Impulse response formalism Linear Maxwell rheology Compressible 1D structure Time-dependent ocean function Near-field water influx

14. SUMMARY ● Forward modelling shows: (1) FENN+BARENTS ice model produces significantly better fit compared to ICE-3G. (2) Viscosity inference relatively insensitive to ice model. (3) GIA model can account for most of observed signal. ● Inverse modelling shows: (1) Depth sensitivity to viscosity is site dependent. (2) Data can resolve two-layer upper mantle structure and a lower mantle layer to a depth of ~1200 km. ● Residual signal to be explored further: (1) Neotectonics. (2) Dynamic ice models. (3) Lateral variations in earth structure.