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The westward drift of the lithosphere: A rotational drag?

B. Scoppola¹, D. Boccaletti², M. Bevis³, E. Carminati⁴ and C. Doglioni^,5

¹ Dipartimento di Matematica, Università Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy
² Dipartimento di Matematica, Università La Sapienza, P.le A. Moro 2, 00185 Roma, Italy
³ Department Civil Environmental Engineering and Geodetic Science, Ohio State University, 2070 Neil Avenue, Columbus, Ohio 43210-1275, USA
⁴ Dipartimento di Scienze della Terra, Università La Sapienza, P.le A. Moro 5, 00185 Roma, Italy
⁵ Dipartimento di Matematica, Università La Sapienza, P.le A. Moro 5, 00185 Roma, Italy

Net westward rotation of the lithosphere relative to the underlying mantle is a controversial phenomenon first attributed to tidal effects, and later to the dynamics of mantle convection. In spite of a number of independent geological and geophysical arguments for westward tectonic drift, this phenomenon has received little recent attention. We suggest that this differential rotation is a combined effect of three processes: (1) tidal torques act on the lithosphere generating a westerly directed torque decelerating Earth's spin; (2) the downwelling of the denser material toward the bottom of the mantle and in the core slightly decreases the moment of inertia and speeds up Earth's rotation, only partly counterbalancing the tidal drag; (3) thin (3–30 km) layers of very low viscosity hydrate channels occur in the asthenosphere. It is suggested that shear heating and the mechanical fatigue self-perpetuate one or more channels of this kind, which provide the necessary decoupling zone of the lithosphere.

Key Words: Earth's rotation • westward drift • lithosphere • asthenosphere viscosity • decoupling

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