Sensitivity of relative sea levels and crustal velocities in Laurentide to radial and lateral viscosity variations in the mantle

Sensitivity kernels are normally used in the inversion of mantle viscosity profile from postglacial rebound observations. In this paper, they are used for the planning of geodetic sites—to find the optimal location that is most sensitive to the viscosity in a certain region of a laterally and radially heterogeneous mantle. Thus, the kernels are presented in a slightly different format. These kernels are computed for a spherical, self-gravitating, laterally heterogeneous, incompressible, viscoelastic Maxwell earth with self-gravitating oceans and induced by cyclic glaciation of a simple parabolic ice sheet with size comparable to the Laurentide ice sheet. It is shown that the kernels for relative sea-level data are age dependent—different age of the data at a fixed location can be sensitive to the viscosity at different depth or lateral position in the mantle. For radial velocity data, sensitivity to radial and lateral viscosity changes as a function of location from the ice load and the anomalous viscosity region are investigated. Present-day tangential velocity data are found to display drastically different sensitivity from present-day radial velocity or geoid rate data—with more emphasis on the shallow part of the mantle and directly underneath the ice load. In particular, regions of anomalous viscosity lying under the ice sheet can influence tangential velocities at far away sites.