Geodynamics

Abstract

The purpose of the work is to study the features of seismotectonics of the junction zone of the Oash and Transcarpathian faults in the Ukrainian Transcarpathians. The research methodology combines a complex analysis of geological-tectonic, seismological, geomorphological and geodetic data on the studied area. For the clarification of coordinates and depths of local earthquake foci we applied methods of their hypocenters specification, using a calculated seismological hodograph and kinematic corrections. Geological and geophysical data, in particular on regional profiles, were used to link seismic events to specific geological structures. It was established that a number of seismic events were recorded at depths of 40-52 km in the studied zone, in its northeastern part. They occurred simultaneously with traditional deep localization of seismic sources in the crust of the Transcarpathian depression (0-27 km deep), including at the depths of the sole of thrust sedimentary strata / roof of the pre-Neogene basement of the Transcarpathian depression (2-3 km deep) in the southwestern part of the studied area. Since these earthquakes are spatially localized to the northeast of the zone where the Transcarpathian deep fault is traced by geological and geomorphological data on the surface, they indicate the subduction of the crustal structures of the Transcarpathian trough in this direction under the thrusts of the Folded Carpathians. This is also evidenced by the corresponding slope of the seismofocal zone at the intersection of the Transcarpathian Deep Fault at greater (15-30 km) depths. These and other features of local seismotectonics reflect the so-called "crocodile" tectonics in the Ukrainian Carpathians. The features encompass the reverse, south-west slope of the seismofocal zone at shallower (0-12 km) depths, as well as the features of the relief of the Carpathians in the studied seismogenic zone. They fully correspond to the characteristics of the "alpine" and "terrain" geodynamics of the region, i.e. compression and displacement in the northeastern and eastern directions, respectively. For the first time, the research established the presence of relatively deeper (30-55 km) seismic activity in the earth's crust of the Ukrainian Transcarpathians – in the zone of subduction of the Moho border under the Carpathians in the area of junction of the Transcarpathian and Oash deep faults. Additionally, the geodynamic and tectonophysical justification for its presence was given in terms of combination of "alpine", terrane and asthenolitic geodynamics of the region. Taking into account the features of seismotectonics of the Oash and Transcarpathian faults junction zone will contribute to clarifying the assessment of the characteristics and peculiarities of the spatial distribution of natural geoecological, in particular, seismotectonic risks and hazards in the central part of the Ukrainian Transcarpathians.