Geodynamic studies at the Poltava Gravimetric Observatory based on astrometric and GPS observations

The principles of studying changes in the gravitational field based on joint astrometric and GPS observations are considered. Joint observations at Poltava in 2001.5—2021.8 were analysed (namely, horizontal deformations of the Earth’s surface in the ETRF2014 system based on GPS monitoring and the local vertical line drift based on observations of stars with a prismatic astrolabe).The trends of the meridional projections — the N-components of crustal displacements and the DZ-drift of the vertical line have opposite directions. The observation point shifts to the north at +0.29 mm/yr, and the vertical line drifts to the south at –0.9 mas/yr. The agreement of these parameters is possible supposing (hffi–30 km) a mass build-up in the Poltava rift node zone caused by magmatic activity. According to the EGM2008 gravity field model, the coordinates of anomaly mass are λ=34.5 °E and j=49.85 °N. It lies 27.5 km north of Poltava. Estimates of gravity field disturbances are: at the «Poltava» observation point in the direction of the anomaly dgffi4 mGl/yr, on the surface above the anomaly source — dgffi8 mGl/yr.