Do Solid Earth Tides have a local behaviour? First results from the analysis of 20-year GNSS timeseries

This work presents the first results of the project: Tidal Interplate Lithospheric Deformation of Earth (TILDE) funded by ESA under the NAVISP program (NAVISP-EL1-047). The goals of TILDE project are the estimation of Local Solid Earth Tides (LSET); i.e., models which depends on the geographical position of the selected sites. Furthermore it will investigate possible correlations between LSET and geological/geophysical events, such as tectonic plates movements, earthquakes and volcanic activities. Finally, we test if the adoption of LSET modelling can improve the quality of GNSS geodetic solutions. 73 GNSS stations have been selected all over the world for which a stack of data of 20-year long at least were available. We have processed the data providing the solutions (namely coordinates) with a sampling rate in turn of 1 day (1D) and 3 hours (3H). For each solution, we have in turn switched off (OFF) and switched on (ON) the SET. The solutions with sampling rate of 1D and the OFF mode were used to estimate long periodic constituents (LPC) of LSET; while 3H solutions will be used for shorter ones. We will present the first results achieved working on LPC. A relationship has been found between Love and Shida numbers and the absolute values of the latitudes of the GNSS stations to which they refer to. Their relationship is a convex parabola which has the maximum just close to tectonic equator which has an inclination of about 28.5 degrees, corresponding to the ecliptic angle increased by the moon inclination of five degrees.