The SLR secular gravity variations and their impact on the inference of mantle rheology and lithospheric thickness

A long history of SLR (Satellite Laser Ranging) observations of the geodeti c satellites LBGEOS-I, LAGEOS-II, Starlette and Stella have been analyzed i n order to estimate the time series of the low degree zonal coefficients in the Earth gravity field, up to degree six, and derive their secular drifts . The paper will point out the critical aspects of the analysis process and will compare the estimated zonal rates with other published results. Compa rison of these zonal rates with the results of global, viscoelastic Earth m odels forced by Pleistocenic deglaciation, shows that the SLR retrieved zon als (J)over dot(2) and the lumped odd zonals can be used to infer the upper mantle viscosity and lithospheric thickness. Discrepancies in the viscosit y profiles, required to reproduce the different zonals, seem to indicate on going mass redistribution over the Earth.