11 TPW and Polar Motion as due to an asymmetrical Earth expansion

The possibility of a link between asymmetrical Earth’s expansion and Polar Motions (PM) is investigated, searching for possible mechanisms of inner and/or surface material displacement, which can lead to the observed Chandler Wobble (CW; Eulerian free oscillation) and its secular drift. While the main result of this work is the identification of the possible cause of PM in the diffuse emplacement of new mass in and under the triple point zones, the problem of the continuous excitation of the CW is still not resolved. Only a qualitative argument in favour of a cause of the CW’s excitation by the not uniformity in time (from short, tens of years, to long time scale), low frequency noise or pulsations, of the diapirical flow of mantle material is proposed. The inversion of paleogeography towards geodynamics is performed, and the result is found that the PM’s current parameters can be prolonged in the current geological past up to 100 Myr, reproducing with satisfactory approximation the more reliable true polar wander path and its slowing down around 50 Myr, which was detected by Besse and Courtillot (1991, 2002). The very long pulsation of the expansion rate ‐ a fundamental new acquisition supporting a pulsating tectonic activity of the Earth (see the «Half Spreading Map of the Ocean Floors»; fig. 5.19 in McElhinny and McFadden, 2000, based on Muller et al., 1997) ‐ could be the cause of the modern undetectability of the effects of the Earth’s expansion on LOD and on geodesy. This is because of the minimum of the half spreading rate and tectonic activity occurring today ‐ and the consequent minimum variation of radius and inertial moment ‐, and because the possible compensating effects due to differentiation of the mantle and core, with consequent accretion of the inner core still underway today.