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.

Glacial isostatic adjustment and the radial viscosity profile from inverse modeling

“…While Ekman [1998] has corrected his data by a sea level rise of 1.2 mm yr −1 taken from Nakiboglu and Lambeck [1991], a simple search for a best model fit with the eustatic sea level contribution as free parameter reveals a value of 2.2 mm yr −1 to obtain a minimum misfit for fitting the uplift rate data. This value is above the upper bound of the recent estimate in the IPCC report [ Church et al , 2001] of (1.5 ± 0.5) mm yr −1 , but it is in accordance with more recent uplift rates derived from the BIFROST GPS campaign [ Scherneck et al , 1998, 2001]. We note, however, that a lower value for the predicted eustatic contribution can be achieved by using the a posteriori viscosity profile for the RSL data (Figure 5a).…”

“…Inferences of ice‐ and Earth‐model parameters from these data are consistent with results inferred from the geological record [ Lambeck et al , 1998a, 1998b]. The uplift map based on the mareograph data has recently been reproduced by the BIFROST campaign [ Scherneck et al , 1998, 2001], which used repeated GPS measurements over a station network encompassing the entire Fennoscandian Peninsula.…”

Space geodetic determination of spatial variability in relative sea level change, Los Angeles basin

“…A prominent contributor to VLM is the rebound of the continents associated with the reduction in land ice mass following the last ice age, or post‐glacial rebound (PGR). RSL measured along many high latitude coasts is falling over time [ Woodworth , 1990] and direct GPS measurements have been used to confirm the PGR contribution [ Scherneck et al , 2001]. PGR is a geologic time scale phenomenon that appears as a secular trend component in tide gauge observations.…”

Upper mantle viscosity from continuous GPS baselines in Fennoscandia

“…By comparing these inferences to those previously obtained via single-site velocities , it is possible to gauge the significance of common-mode errors. A similar but less comprehensive study of the baseline length component, L, was presented by Scherneck et al (2001). As baselines are strongly correlated, the present work will extend the previous analysis by considering the correlation of variations in baseline pairs.…”