Realisation of the Non-Rotating Terrestrial Reference Frame by an Actual Plate Kinematic and Crustal Deformation Model (APKIM2020)

Since 1991, the International Terrestrial Reference Frame (ITRF) includes the global time evolution of station positions (velocities) in addition to the three-dimensional Cartesian station positions at a fixed reference epoch. The orientation of the velocities refers to a kinematic model of rigid tectonic plates derived from geophysical observations over millions of years. For consistency with other geodetic parameters (e.g., Earth orientation), the models must be aligned to actual no-net-rotation of the whole Earth surface. Because of deviations of present-day velocities and neglect of non-rigid surface deformations, e.g., in seismic zones, the geophysical models are not valid for today. This paper describes a further developed method of estimating a non-rotating terrestrial reference frame from space geodetic observations. Different to previous estimations of geodetic no-net-rotation models, regional inter-plate and intra-plate crustal deformations are included, and instead of using the irregularly distributed observed station velocities, an evenly distributed grid throughout the Earth is interpolated by least squares collocation. Due to significant changes of the station velocities from one ITRF to another, NNR models must be computed for each ITRF. Here it is done for the ITRF2020.