The purpose of the research is to establish experimentally the most favorable conditions for determining the vertical movements of the Earth's surface in terms of the minimal influence of variations of soil moisture on the results of observations. Geodetic monitoring of deformation processes at geodynamic testing grounds (GTG) occurs mainly without taking into account the influence of factors on the dynamics of the Earth's surface and benchmarks. To successfully separate tectonic or anthropogenic movements from all recorded motions of the Earth's surface, it is necessary to exclude their hydrometeorological component. One type of meteorological impact on the dynamics of the Earth's surface and benchmarks is the volumetric deformation of the swelling soils due to the variation of their moisture. They cause seasonal vertical movements, the magnitude of which depends on the physical and mineralogical properties of the soil, the characteristics of the environment, and the amplitude of annual fluctuations in temperature and moisture. The research methodology included the parallel observations at two points of vertical movements and moisture of the top one-meter layers of soil at GTS in Poltava for the period 2006 to 2015. The main result is the determination of a nonlinear nature of the effect of seasonal changes of soil moisture on the vertical displacement of the Earth's surface, depending on the absolute values of moisture. If soil moisture exceeds its maximum molecular moisture content (MMMC), then its variations do not affect the dynamics of the ground. This is explained by the different mechanism of vertical infiltration of water in the soil, depending on its water saturation. At high levels of soil moisture, further changes are caused mainly by capillary and gravitational forces that do not cause deformations and vertical movements of the Earth's surface. The scientific novelty of this research is to establish the important role of the MMMC of soil in the generation of vertical movements of the Earth's surface and benchmarks due to variations in its moisture. The practical significance of the work lies in the possibility of minimizing the influence of hydrometeorological factors on the results of high-precision observations of the dynamics of the Earth's surface. The results obtained can be used in the organization of high-precision observations of vertical movements on the GTG and their interpretation.
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