BIFROST project: 3-D crustal deformation rates derived from GPS confirm postglacial rebound in Fennoscandia

Abstract

Since autumn 1993 the BIFROST project has provided daily GPS solutions of geodetic positions from a network of more than 40 stations covering a large area of the Baltic shield. This area is expected to show large vertical motion due to glacial isostatic rebound following the deglaciation at the end of the Pleistocene. This paper will discuss the inference of three-dimensional rates of crustal motion at the GPS stations with respect to (1) a plate-fixed average for the horizontal components; (2) a geocentric reference in order to infer absolute changes of sea level from vertical crustal motion and models of geoidal rebound. We show that the horizontal strain rate pattern is largely dominated by unilateral extension and not exhibiting horizontal shear to an important extent. In regard to the vertical motion a crucial issue is the stability of the geocentre in the GPS frame. We show results from an Empirical Orthogonal Function analysis that attenuates regionally correlated noise. In all components our observations suggest reasonably close agreement with forward computions on the basis of postglacial isostatic adjustment. A dominant tectonic signal would lead to a certain fraction of the batch of baselines to exhibit shortening. A tectonic process leading to a similar pattern of horizontal motion as expected from postglacial rebound can safely be dismissed in the context of the currently accepted plate tectonic setting. Thus, our baseline rate comparison will be a critical first order test of the prevailing style of deformation.