The westward drift of the lithosphere. A tidal ratchet?
Is the westerly rotation of the lithosphere an ephemeral accidental recent phenomenon or is it a stable
process of Earth’s geodynamics? The reason why the tidal drag has been questioned as the mechanism
determining the lithospheric shift relative to the underlying mantle is the apparent too high viscosity of
the asthenosphere. However, plate boundaries asymmetries are a robust indication of the ‘westerly’
decoupling of the entire Earth’s outer lithospheric shell and new studies support lower viscosities in the
low-velocity layer (LVZ) atop the asthenosphere. Since the solid Earth tide oscillation is longer in one side
relative to the other due to the contemporaneous Moon’s revolution, we demonstrate that a non-linear
rheological behavior is expected in the lithosphere mantle interplay. This may provide a sort of ratchet
favoring lowering of the LVZ viscosity under shear, allowing decoupling in the LVZ and triggering the
westerly motion of the lithosphere relative to the mantle.