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Geodynamics 1(28)/2020 GEOPHYSICS UDC 540.34:525.62:551.24 E. KOZLOVSKYI, V. MAKSYMCHUK, D. MALYTSKYY, V. TYMOSCHUK, O. HRYTSAI*, N. PYRIZHOK Carpathian Branch of Subbotin Institute of Geophysics of NAS of Ukraine, 3-B Naukova Str., Lviv, 79060, Ukraine, *e-mail: [email protected] https://doi.org/10.23939/jgd2020.01.062 STRUCTURAL-TECTONIC AND SEISMIC CHARACTERISTICS RELATIONSHIPS IN THE CENTRAL PART OF THE TRANSCARPATHIAN INTERNAL DEPRESSION Purpose. To investigate structure-tectonic and faults features of the central part of the Transcarpathian internal depression and their relations with earthquake epicenters localization and peculiarities of seismic waves spreading on the base of instrumental observations in regime geophysical observatories of the Carpathian geodynamic polygon. Methods and results. The study developed methodology for specification of local earthquake focus depths by means of neuron-network modeling, computer processing and systematization of observation data at the Carpathian geodynamic network and adjusting areas on the basis of recent mapping and graphical information. On the examples of earthquakes registered by the regime geophysical station “Mukachevo”, focal mechanisms of earthquakes were determined using first arrival polarities. Scientific novelty. The research determined the relationships between structural and tectonic features in the central part of the Carpathian backdeep, the recent geodynamics of the region’s basement, peculiarities of seismic waves spreading, and formation of local earthquake focuses. It was stated that the influence of the igneous rocks of the Vyhorlat-Hutyn volcanic ridge significantly reduced the time of seismic waves passing in the sedimentary layer and partly in the basement. To determine a focal mechanism of the earthquake, the velocity of seismic waves in the layers should be taken into account on a case-by-case basis, taking into account the location of seismic stations with respect to deep and surface faults and the impact of volcanic rocks, and not using standard velocity models for seismic stations resulting from the stations that give significant results in calculations of output seismic wave angle and facilitate the selection of nodal surfaces. Practical value. Detailed investigations allow determining characteristics of earthquake epicenters, velocities and direction of seismic waves spreading in accordance with the structure of the basement and sedimentary layer. This will, in turn, provide an opportunity to supplement the data of long-term monitoring of natural and technological hazards in the region. Key words: Transcarpathian internal depression, tectonic displacements, Vyhorlat-Hutyn volcanic ridge, earthquake epicenters, nature of earthquake source. Introduction However, the extension of tectonic displacements is not only straightforward, longitudinal or transverse, The Transcarpathian internal depression in the it is also characterized by a more complex north-east contacts the area of the Pienin ridge and the configuration. Three structural and tectonic levels can Marmarosh crystalline massif. It borders on Maramu- be defined in the structure of the backdeep. They resh basin in the south-east, the Panonian depression include the Paleozoic, Mesozoic-Paleogene and Neo- in the south-west, and it turns into the East-Slovak gene levels. The first two are the basement of the depression in the north-west [Krupsky, 2001]. Transcarpathian internal depression, and the thickness The recent tectonic structure of the Transcar- of the latter exceeds 3 km. The Transcarpathian pathian internal depression is characterized by the internal depression is divided into several zones with intense dislocation, the presence of faults and peculiarities of a seismic regime which are identified displacements in longitudinal and cross directions. The with the tectonic structure. These zones consist of the Transcarpathian (Pieninic) and Panonian deep faults Chop-Mukachevo and Solotvin depressions The have the most amplitude among them. [Hnylko, 2011; Oashi fault is the border between them [Pronyshyn, Hnylko, 2012]. The similarly-named Transcarpathian & Pustovitenko, 1982]. (Pieninic) fault separates the internal depression from The zones, distinguished in the study, differ in a the Pienin zone, and the Panonian fault from the sequence type, according to earthquakes repetition Panonian depression, respectively. Some researchers patterns, the amount of energy, the speed of released [Krupsky, 2001] single out up to 12 regional conditional deformations, and their activation over longitudinal and 9 crossing faults which divide the time. [Pronyshyn, & Pustovitenko, 1982; Pronyshyn, depression into a series of rectangular blocks. & Kuznetsova, 2011; Maksymchuk, et al., 2014]. 62 © E. Kozlovskyi, V. Yu. Maksymchuk, D. V. Malytskyi, V. R. Tymoschuk, O. D. Hrytsai, N. B. Pyrizhok Geophysics It was possible to define the presence of three se magmatic activity were formed, and as a result of ranges of epicenter concentrations along the Carpa- the collision through magma conducting channels, thians associated with the Transcarpathian (Pieninic) magmatic rocks, which were in the bottom of the deep and Panonian deep faults, as well as with the axial trenches during the stretching, appeared on the fault zone of the Neogene Transcarpathian internal surface. depression [Melnychuk, 1982]. The connection of the Magmatic Alpian formations can be divided into Transcarpathian earthquakes with crossing faults is two types: the one which appeared at the stage of investigated in a number of works [Pronyshyn, & stretching, and the other which corresponds to a stage Pustovitenko, 1982; Pronyshyn, & Kuznetsova, 2011; of collision. Magmatic formations of the first type are Seghedia, 2004]. represented by complexes that are common in the Purpose Marmarosh, Pienin zones and in the Rakhiv-Burkut tectonic group of zones. In the basement of the Investigations of tectonic structure and fault Transcarpathian internal depression, the ophiolite tectonics with the localization of epicenters of complexes were determined by the results of drilling earthquakes interrelations in the central part of the (hyperbasites, basalts, diabases, andesite basalts, Transcarpathian internal depression and peculiarities trachites, basalt tufts and deep-water sedimentary of seismic waves spreading on the basis of rocks with the undergone metamorphism after an instrumental observations at regime geophysical stations (RGS) in the Carpathian geodynamic network influence during contact with volcanic rocks). The .Methods and results magmatism of the collision stage is connected directly The structure of the Ukrainian part of the with the formation of the molas of the Carpathian region depends on the geodynamics in the Transcarpathian internal depression and its products Alpine period, when there were rapid geological have an autochthonous nature. Volcanic rocks of the development variations. Passive rifting (spreading) in final stage - lava formations of the Vyhrolat-Hutin the middle and late Triassic, Jurassic and early ridge – are the youngest formations of the Ukrainian Cretaceous has changed into a collision. At the first Carpathians formed after the accumulation of the stage, crushing zones, deep-ocean troughs with inten- Neogenic molasses in the Transcarpathians (Fig. 1). Fig. 1. Scheme of magmatic rocks distribution in the Transcarpathian internal depression [Medvedev, 2015] 1 – Transcarpathian internal depression ; 2 - 8 - Miocene magmatic complexes: 2 – Novoselytsya acidic tuffs (a) and Baden ignimbrites (b) complexes; 3 – Dobrobrat volcanic-sedimentary complex (Sarmat); 4 – Vyhorlat- Hutyn complex (Pannonian-Pliocene); 5 – intrusions (a – acidic, b – basic); 6 – volcanic centers; 7 – hidden volcanic centers; 8 – boundaries of magmatic complexes distribution (a – on the surface, b – hidden);9 - schematic representation of tectonic faults; 10 – rivers: 1-Latoritsa, 2-Tysa, 3-Tereblia, 4-Teresva, 5-Black Tysa 63 Geodynamics 1(28)/2020 According to researchers [Kruglov, et al., 1985; processes needed a detailed study. Their purpose was Starostenko, 2013], early Alpine magmatism of the to develop a methodology for studying earthquake Transcarpathians is enclosed in the interval of the precursors. The relevance of those studies at the Jurassic-Early Cretaceous. Other lower boundary time network was due to the significant seismic activity of is fixed in the Triassic. the Transcarpathians, high population density, All the studies indicate that the Mesozoic concentration of industrial enterprises, and main oil and volcanism of the Ukrainian Carpathians did not appear gas pipelines of international importance. once, but in several phases during the late Triassic- Therefore, it was necessary to organize early Cretaceous, that is, high magmatic activity permanent observations in regime geophysical stations remained in the region for about 100 million years. (RGS) in order to define time-series variations in the The significant number of crossing tectonic geophysical parameters of local anomalies which are displacements with the northeastern orientation divides directly related to the preparation of local earthquakes the Transcarpathian internal depression into several [Maksymchuk, et al., 2001]. During a short period of rectangular blocks and crosses the NW part of the time, from 1985 to 1995, the territory of the network Carpathian fold structures almost at right angles. Such was constructed, equipped, and the RGS stations Brid, faults

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