International Journal of Physical Sciences Vol. 1 (2), pp. 085-092 October, 2006 Available online at http://www.academicjournals.org/IJPS © 2006 Academic Journals Full Length Research Paper Seismicity of the Carpathian region Dmytro Malytskyy Carpathian Branch of Subbotin Institute of Geophysics, Department of Seismotectonic Researches, 3-b,Naukova st. 79060 Lviv, Ukraine. E-mail: [email protected]. Accepted 19 October, 2006 Carpathian complex prognostic poligon has being created for testing of new methods and equipment and their implementation into the practice of seismotectonic investigations in the Transcarpathians. The polygon consists of a network of regime geophysical stations (RGS). I analyzed seismicity of the Ukrainian sector of the Carpathians. It is determined by local earthquakes and strong subcrustal earthquakes of the Vrancea zone in Romania. In this paper, I estimate the most fundamental parameters describing earthquakes: seismic energy E and energy class K=log(E) in a time window of 40 years (1961-2001). Our results show that, the E 1/ 2 plot against time may be a good tool for understanding of a local earthquake activity, although the shape of the plot is strongly influenced by extreme events. Also, we have found a correlation between seismic moment M0 and energy class K of the local earthquakes for Transcarpathian region. Key words: seismicity, energy class, seismic energy, seismic moment, geodynamic polygon, catalogue INTRODUCTION The Carpathian Arc which stretches for about one and year, seismic stations register dozens of local half thousand kilometres is a fragment of the northern earthquakes with magnitude exceeding 2.5. However, the branch of the Alpine Mediterranean Belt in Eurasia strong earthquakes occur rarely. Seismicity of the (Reports of Geodesy, 1998). In the East, within the Ukrainian part of the Carpathian arc is described in the Ukrainian segment, it already completely overlies the works by Yevseyev, Pronyshyn, Pustovitenko, folded framing of the ancient platform and “splashes out” Riznichenko, Kharitonov, Verbitsky and Kendzera far over the foredeep of the pre-Riphean Eastern – [Reports of Geodesy, 1998; Latynina et al, 1995; Somov European Platform. The whole area of the Internal and Rahimova, 1983; Verbytsky, 1977,1984, 1985,1994; Carpathians is distinctly divided into two different parts. Pidstrygach and Checunov, 1978; Riznichenko, 1979; The larger western part, located within the Slovakian and, Pronyshyn and Pustovytenko 1982; Vasilyenko et partially, Polish territories, is represented by the al,1979; Shlyahovyi and Ostrovskyi 1984; Verbytsky et mountainous massif of the Small and White Carpathains. al,1986; Earthquake Prediction, 1984; Verbytsky and The smaller eastern part of the Internal Carpathians, Fedoryshyn 1987]. situated to the east of the systems of the Gornad faults, The Transcarpathian seismogenic zone is remarkable consists of several separated basins namely the Eastern- for the highest seismicity in the Carpathian Region. Local Slovakian, the Mukachevo and the Solotvyno basins. earthquakes with intensity upto 70 on the MSK scale were They form a rear molasse foredeep which is known in registered here [Reports of Geodesy, 1998]. (Tyachiv, Ukraine as the Transcarpathian Depression. In the zone 1781, 1870; Sighet, 1784, 1823; Rokoshyno, 1797; of the Southern and Eastern Carpathians (Vrancha zone) Dovhe, 1872, Svalyava, 1908; Teresva, 1926; Dragovo, the regularity in the location of hypocentres of the 1937 [Pidstrygach and Checunov, 1978]. In accordance earthquakes has been revealed. Inherent seismicity of with the data about peculiarities of seismic regime in the Carpathians is determined by the earthquakes from local Transcarpathians two seismically dangerous zones are origion zones, located within the limits of tectonic separated which are Mukachiv and Tyachiv zones structures, forming the mountain structure, foremountain Oashski fracture is likely to be a boundary between them troughs and slopes of adjacent platforms [Reports of [Pidstrygach and Checunov, 1978, Pronyshyn and Geodesy, 1998]. Instrumental study of seismicity in the Pustovytenko 1982]. Local earthquakes with intensity up 0 Carpathian region was started end of 19th century. Each to 8 on the MSK scale (Kmax = 14) are possible in the 086 Int. J. Phys. Sci. Mukachiv seismically dangerous zone. Earthquakes with In the Eastern Carpatians triangulation measurements an intensity of 70 on the MSK scale occur with a time were repeated in 50-s. During 75 years triangulation intervals of 160 years. The last such earthquake was points have displaced by 50 cm. Angulation measure- registered on January 5th, 1908 with its epicenter south ments are carried out in the Western Carpathians at 4 of Svalyava. Seismic risk of an earthquake with an local polygons. During 30 years the points have displaced intensity of 70 on the MSK scale approaches 0.5 in the by 30-50 cm. Distribution of horizontal displacements Mukachiv seismically dangerous zone. corresponds to radial extension of the Pannonian Trough The last earthquake with an intensity of 60 on the MSK (Somov, 1983). scale was registered on October 24th, 1965 with the Latynina considers the results of extensometric moni- epicenter close to Beregove. During some tens of years toring in the Carpathian region. Extensometric stations there have been no considerable tremors in this zone. were set up by experts from Hungary, former Czechoslo- This testifies the growth of probability for a strong vakia and the Soviet Union in 80-s on the basis of quartz earthquake in the Mukachiv seismically dangerous zone. extensometers elaborated in the Institute of Physics of Creation of an automated system for warning of strong the Earth AS USSR (Latynina, 1993). earthquakes is an urgent problem regarding considerable Beregove stations are located within the Transcar- seismic activity in the Transcarpathians, growth of pathian Inner Trough at a distance of 50 km from a deep seismic danger in the Mukachiv zone, high density of fault at the boundary of the Folded Carpathians. Intensive population, high concentration of industry and internatio- rock compression with a speed of 30⋅10-7 per year is nal oil and gas pipelines. Detailed studies on the nature registe-red at the station Beregove-1 in the near- latitude of seismotectonic processes in the Transcarpathians and direction (azimuth 73°) perpendicular to the Eastern mechanisms of preparation and realization of local Carpathians stretch. In another direction in azimuth 37° earthquakes are necessary to develop such a system. compression with a speed 5⋅10-7 per year is observed. Seismotectonic processes of a tectonic earthquake are Rock compression with a speed of 5⋅10-7 per year is accompanied by certain changes both in stress-strain registered in azimuth 140° at the station Beregove-2; the state of the Earth’s crust and fracture system of rocks. second device with a small base doesn't provide with Distribution of both stresses and strains in the Earth’s reliable measurements (Latynina, 1995). crust and spatial-temporal movements of its surface According to extensometric data at the station Bere- during earthquake commencement is of complex gove the following values of linear deformation velocities character significantly dependent on tectonic structure of -7 -7 are obtained: exx=-33.5⋅10 /year and eyy=+12.8⋅10 /year the Earth’s below and orientation of active tectonic forces in latitudinal and meridional directions, respectively. [Riznichenko, 1979; Pronyshyn and Pustovytenko, 1982; Shearing deformation is small in comparison with linear Aki and Richards, 1983; Kasahara 1985; Verbytsky et al, deformations. Consequently, main deformations are orie- 1986; Earthquake Prediction, 1984; Verbytsky et al, nted according to directions close to latitudinal and 1987; Malytskyy,1998; 1999; 2000]. Thus, important meridional. information about seismotectonic processes in the Deformation velocities averaged for the 75-year period Earth’s bowels may be obtained by investigation on are 15-30 times as lower than velocities obtained during strains and modern movements of the Earth’s crust. deformation monitoring (Reports of Geodesy, 1998). Geodetic methods for studying the Earth’s surface As all rocks are somewhat fractured and tensosensi- modern movement (high precission levelling and triangu- tive, the physical-mechanical properties (elasticity, electri- lation) are characterized by discrete measure-ments and cal conductance, heat conductance, permeability, stren- may be efficiently used at displacement velocities excee- gth etc.) and related geophysical fields are sensitive to ding several mm per year [Vasilyenko Yet al, 1968]. the stressed-strained state variations of the Earth's Application of the global satellite system of coordinate (Verbytsky, 1977, 1984; 1985, 1994). During the Earth's determination (GPS) for monitoring of the Earth’s surface crust stressed-strained state variations the inner structure modern movements is more promising. of rock massifs is also changed; this process is accompa- Carpathian complex prognostic poligon is being created nied by emission of elastic and electromagnetic waves for testing and implementation of new methods and (acoustic, seismic and electromagnetic emissions). Thus equipment in seismotectonic investigations in the Trans- there exist physical prerequisites for studying geodyna- carpathians, as well as to ascertain seismic danger in the mic processes by geophysical methods which explains territory of Carpathian