Long-term true polar wander of the Earth including the effects of convective processes in the mantle and continental drift

Long-term true polar wander (TPW) of the Earth was examined by taking into account the effects of simplified convective processes in the Earth's mantle and continental drift. The TPW, for a given viscoelastic earth model, is wholly determined by both the magnitude of non-forcing elements of moment of inertia (I₁₁, I₂₂ and I₃₃) and I₁₂ element of product of inertia, and the rates for forcing elements, dI₁₃/dt and dI₂₃/ d_t. The forcing rates are largely related to time-dependent convective processes in the mantle and also continental drift. In this study, I examined the TPW on a convecting mantle with oscillating moments of inertia, inferred from a convective process of alternating degree-one and degree-two structure changes of mantle convection by Zhong et al. (2007). In the phase for a relatively hydrostatic Earth, corresponding to largely degree-one planform, the predicted TPW is sensitive to the viscosity structure of the mantle, particularly to the lithospheric viscosity structure, and its magnitude may be larger than ∼30° even for the forcing rates with ∼10³⁰ kg m² Myr^-1 related to continental drift (Dickman 1979). In the phase for a non-hydrostatic Earth characterized by largely degree-two planform such as for the present-day, however, the TPW is less sensitive to the viscosity structure, and its magnitude may be ∼10° at most. These results may provide quantitative constraints on examining relationship between rheological structure and convective processes in the mantle, continental drift and TPW.