Effects of lateral viscosity variations on present-day horizontal motions and baseline deformations due to glacial isostatic adjustment

By means of a finite element algorithm we investigate the effects of lateral viscosity variations upon the horizontal motions currently detected by Very Long Baseline Interferometry (VLBI) in Europe. Our approach is based on a suite of flat Earth models including a layered compressible Maxwell mantle and regions of anomalous viscosity localized both in the lithosphere and in the upper mantle. A detailed study of horizontal velocities expected in the periphery of the Fennoscandia ice-sheet is followed by a comparison between VLBI data and model predictions. Our results show that the rates of horizontal deformations are greatly sensitive to both lateral viscosity variations and deep mantle stratification, especially close to the margins of the ice sheet. We have found that among the Earth models studied here, those including both lateral variations and a sharp increase of mantle viscosity across upper and lower mantle are the most suitable to ‘explain’ the rates of horizontal velocity currently observed in Europe.