FEATURES OF RELIEF OF THE BORZHAVA RIVER MIDDLE FLOW AREA AND THEIR CONNECTION WITH GEODYNAMICS AND SEISMOTECTONICS

Abstract

With attraction of the newest (until 2010–2022 inclusive) geological-geophysical and geodetic data and geological-tectonic construction, the features of relief of the Borzhava River middle flow area (Ukrainian Transcarpathians) were analyzed, including peculiarities of the morphology of the river valley, their connection with the geodynamics and seismotectonics of the territory is traced. In the interval between Keretsky and Dovge villages the river flows in the valley of south – southeast direction between the southwestern slopes of the Folded Carpathians and northeastern slopes of Vygorlat-Guta volcanic ridge, tracing the near-surface localization of Transcarpathian deep fault zone geological structures (fault-suture, i.e. contact zones of the tectonic structures of the Transcarpathian depression and the Folded Carpathians). In the Dovge village river terns to the southwest and crosses the Vygorlat-Guta ridge in this direction in the interval to the Velyki Komyaty village, its valley here is associated with rupture discontinuities of the diagonal Borzhava fault zone. The place of terns of the Borzhava River in the Dovge village is connected with the area of junction of the structures of the Borzhava fault zone and the Transcarpathian fault-suture zone. The Onok height and the Velykyy Sholles volcanic ridge, which surround it from the southeast and east, are connected with influence of the diagonal Vynohradiv and meridional Oash faults. In the northeastern parth of studied area, under the mountain ranges of the Kuk – Palenyy Grun` ridges, a relatively deep (40–55 km) zone of seismic activity was discovered, it is related to the area of junction of the deep tectonic structures of the Transcarpathian and Oash fault zones, the first of which dips in the northeast direction under the Carpathians, and the second (its tilted subfault) dips in the eastern direction under the structures of the Solotvyno depression. Also regular, including the newest (2 perceptible earthquakes since the beginning of 2023) seismic activity (mainly at the depths of the pre-Neogene basement (2–6 km)) is demonstrated in the studied area (along with fault-block structures of the Transcarpathian trough and fold-thrust structures of the Folded Carpathians) by the structures Borzhava fault zone (orthogonal to the Carpathians, mini-graben in structure) and conjugated with it, the more submeridional Shalanky-Irshava (slightly sigmoid in plan) and Petrovo-Ardanovo faults. The genesis of the specified peculiarities of the relief and seismicity of the studied area is analyzed from the point of view of a combination of "alpine" (thrust-subduction of the crustal structures of the Transcarpathian depression and sedimentary strata of the modern Folded Carpathians to the northeast – the so-called multi-tiered "crocodile" tectonics), present "terrain" (shift to the east of the crustal structures of the Transcarpathian depression – northeastern end of the Alkapa terrane – superimposed, relatively low-amplitude process) and "asthenolitic" ("spreading" of convective flows from the asthenolite under Pannonia) components of late Neogene ("post-magmatic", up to 5–7 million years ago) and modern regional geodynamic process. Key words: Ukrainian Transcarpathians; Borzhava River valley; cross section; channel slope; faults; geodynamics; earthquake; seismotectonics.