Abstract Maree solide

366

While mantle convection is a fundamental ingredient of geodynamics, the driving mechanism of plate tectonics remains elusive. Are plates driven only from the thermal cooling of the mantle or are there further astronomical forces acting on them? GPS measurements are now accurate enough that, on long baselines, both secular plate motions and periodic tidal displacements are visible. The now >20 year-long space geodesy record of plate motions allows a more accurate analysis of the contribution of the horizontal component of the body tide in shifting the lithosphere. We review the data and show that lithospheric plates retain a non-zero horizontal component of the solid Earth tidal waves and their speed correlates with tidal harmonics. High frequency semidiurnal Earth’s tides are likely contributing to plate motions, but their residuals are still within the error of the present accuracy of GNSS data. The low frequency body tides rather show horizontal residuals equal to the relative motion among plates, proving the astronomical input on plate dynamics. Plates move faster with nutation cyclicities of 8.8 and 18.6 years that correlate to lunar apsides migration and nodal precession. The high frequency tidal oscillations are mostly buffered by the high viscosity of the lithosphere and the underlying mantle, whereas low frequency body tides are compatible with the relaxation time of the low-velocity zone and are able to westerly drag the lithosphere over the asthenospheric mantle. Tidal oscillations also correlate with the seismic release.