Use of ocean tide loading deformation to constrain tomographic models of the Earth

Ocean tides periodically load Earth's surface and thereby introduce deformations. Despite being small in amplitude, surface deformations caused by the strongest tidal constituents can be reliably extracted from GPS data. The resulting signals are sensitive to the material properties of the Earth's interior across a broad range of spatial and temporal scales. This makes it a useful and potentially unique source of information about the planet's response at low frequencies and is complementary to models of the Earth inferred from seismic data. Although the latter is commonly used to constrain Earth's interior, short-period seismic waves are generally insensitive to density. In contrast, previous research indicates that the ocean tide load (OTL) surface displacements may be sensitive to both the elastic properties of the interior as well as to the mass distribution in the lithosphere and, perhaps, the upper parts of the mantle.Comparisons between observed OTL surface displacements and corresponding modelled responses for a suite of 1D reference models yields residuals of up to 0.3 mm (Martens et al., 2016). Regional-scale spatial coherency in the residuals suggests sensitivity to relatively long-wavelength deviations from the globally-averaged Earth structure. By resorting to a finite-element method to solve the 3D elastostatic momentum equation, we investigate whether part of these discrepancies can be explained by 3D structure that are in global tomographic models. The validation of current seismic tomographic models against independent geodetic observables (GPS data) represents a first step towards the self-consistent integration of geodetic and seismic data to image Earth’s crust and mantle.