Post glacial rebounds measure the viscosity of the lithosphere

Abstract

The observed higher uplift rates before the end of deglaciation requires the existence of a low viscosity channel or layer. The uplifts observed after the end of deglaciation does not show any contribution from this low viscosity channel and a homogeneous viscosity model fits very well to the observed uplift. Most of the researchers therefore prefer the homogeneous model and suggest that the higher uplift rate before the end of deglaciation is the result of elastic contamination. It has been shown that the elastic deformation of the lithosphere is far too small to be responsible for the observed extra uplift; therefore, the homogeneous viscosity model should be discredited. The homogeneous viscosity of the postglacial period and the high uplift rate of the late glacial period can be explained with a model which has an upper layer determining the homogeneous viscosity and the layer below it which has a low viscosity. The contribution to the uplift of this low viscosity layer is indistinguishable from an instantaneous uplift. Current GPS deformation measurements indicating 10^21 Pas average viscosity for the lithosphere, which is consistent with this model. The viscosity of the low velocity zone should be between 10^18 Pas and 10^11 Pas. The lower constrain on the viscosity of the low velocity zone can be deduced from seismic observations. This viscosity model is consistent with post glacial rebounds and further supported by the lack of the dynamic topography.