Recent Vertical Movements of the Earth's Surface on Southern Sakhalin Island from GNSS Observations

In the regional structural-neotectonic aspect, southern Sakhalin Island consists of three uplifts with submeridional orientation and two troughs separating them. The organization of a geodynamic GNSS (Global Navigation Satellite System) observation network in the south of the island made it possible to estimate the secular vertical movements of the Earth's surface based on interseismic rates in the ITRF (International Terrestrial Reference Frame) coordinate system. Interseismic vertical movements of neotectonic structures were determined based on data from 29 GNSS observation points, where three to six cycles of periodic measurements were carried out from 1999 to 2012. A characteristic feature of interseismic movements is uplift of the south of the island at an average rate of 1.1 mm/year, which is consistent with geological and geomorphological studies of the neotectonic stage of the region's evolution. The highest rates (1.0-1.6 mm/year) are associated with uplifts, while relatively lower rates (0.6-0.7 mm/year) are found in depressions. The revealed heterogeneities in vertical movement rates in depressions are reflected in the regional field of horizontal deformations and kinematics of faults that bound the depressions. The obtained estimates of the secular rates of neotectonic structures differ from the map of recent vertical movements of the Earth's crust. Sakhalin (hereinafter referred to as the RVMEC map), compiled in the late 1970s from repeat measurements of the leveling network and data from sea level observation posts. According to the RVMEC map, most of the south of the island was characterized by subsidence of the Earth's surface at rates of up to 7-8 mm/year, which manifested itself both within the newest uplifts and depressions and was interpreted as secular tectonic movements. Strong seismic events that occurred in the south of the island during the period of repeated measurements of the leveling network (1959-1977) distorted the RVMEC map as one of secular tectonic movements.