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Abstract:
The realisation of the International Terrestrial Reference Frame (ITRF) requires no rotation with respect to the entire Earth surface. In practise, this is normally done by transforming the ITRF station velocities to the geophysical model NNR NUVEL-1A (DeMets et al. 1994). The problem is that the NNR NUVEL-1A presents the average plate motion over millions of years and is not representing the present-day surface motions. Furthermore, it does not include any crustal deformation (e.g. the Circum-Pacific belt and the Mediterranean deformation zone) but only rigid motions of 12 tectonic plates.The present paper integrates the actual station velocities of the Terrestrial Reference Frame over the entire Earth surface and reduces the common motion due to actual crustal deformation to a non-rotating frame. The continuous global surface velocity field is achieved by a least squares collocation procedure with empirical correlation functions. The result shows a global rotation of the actual ITRF in the millimetre-level, i.e. significantly greater than the ITRF precision. Regional reference frames (e.g. SIRGAS, EUREF) are using the ITRF as the reference and are thus affected by its global rotation. As an example, we are modelling the deformation of the Latin American region represented by the geocentric reference system for America (Sistema de referencia para las Américas, SIRGAS) by a regional velocity model for SIRGAS (VEMOS). It is demonstrated that there is a significant regional contribution to the common rotation of the ITRF.
