COMPARISON OF THE COMPLETE AND TRUNCATED VERSIONS OF THE POLAR WANDER EQUATIONS.

The paper presents a theoretical development of a uniformly valid solution for describing the polar motions of a layered viscoelastic earth. Such solutions require the usage of two classes of eigenspectra to describe the processes of rotational deformation and viscous relaxation. One set consisting of real eigenvalue describes the isostatic relaxation of the mantle by viscous creep. The second one governs the readjustment of the rotational axis of the viscoelastic earth, and the eigenspectrum is complex valued. These solutions are capable of describing rotational phenomena ranging from Chandler wobble excitation to long-term polar drift. A comparative study is conducted between the complete solution for polar wander and one in which a number of the rotational modes has been truncated. For a four-layer model consisting of an elastic lithosphere, a two-layer, adiabatically stratified viscoelastic mantle, and an inviscid core, such a comparison shows that at most a 30% difference exists in the viscosity solutions of the lower mantle, which are obtained by fitting the theoretical predictions to the observed polar wander data.