Source mechanism and tectonic setting of 29.09.2017 earthquake near Stebnyk
Received: April 05, 2018
Revised: May 29, 2018
Accepted: June 12, 2018
Carpathian Branch of Subbotin Institute of Geophysics of NAS of Ukraine
Carpathian Branch of Subbotin Institute of Geophysics of the NAS of Ukraine
Carpathian Branch of Subbotin Institute of Geophysics of NAS of Ukraine
S. I. Subbotin Institute of Geophysics of the National Academy of Sciences of Ukraine
Carpathian branch of Subbotin Institute of geophysics of NAS of Ukraine
Carpathian Branch of Subbotin Institute of Geophysics of NAS of Ukraine
Carpathian branch of the Institute of Geophysics named after S.I.Subbotin of the National Academy of Sciences of Ukraine

Purpose. The paper’s purpose consists in determining the source mechanism of 29.09.2017 earthquake near Stebnyk (21h46m8,4s, = 49,34˚, λ = 23,49˚, h = 1,9 км, MD = 2,9) using two methods – from polarities of first P-wave arrivals and by inversion of wave forms registered at a limited number of stations. Methodology. Seismic waves in the inhomogeneous medium represented by horizontally layered elastic structure are calculated using the matrix method. Expressions derived for the field of displacements on the upper surface are used for the determination of seismic moment tensor rate by isolating only direct P-waves. Also, the source mechanism is determined from polarities of first P-wave arrivals. Result. In the paper, a new method is presented for determination of earthquake source mechanism by inversion of only direct P-waveforms registered at only a limited number of stations and from polarities of first P-wave arrivals at seismic station. The conclusion is drawn out that mechanism simultaneously determined from polarities of first P-wave arrivals is more reliable. Correlation hogging of the earthquake characteristics and its source mechanism with tectonic setting of the region enables to associate the earthquake with thrusting of second order within the extent of allochtonous part of the Sambir nappe. Originality. The inversion of waveforms of only direct P-wave, proposed in the paper, make it possible to determine the focal mechanism of the earthquake by using the data of a small number of stations. It is especially important in regions with relatively low levels of local seismic activity, which include Precarpathians. The mechanism of the earthquake near Stebnyk of 29.09.2017 is one of the first, determined within the extent of the Сarpathian Foredeep; and comparison of the mechanism with the geological structure data of the region made it possible to ascertain the probable tectonic preconditions of the earthquake and to associate it with  landslide near the city of Stebnyk. Practical significance. One of the nodal planes of the source mechanism determined in the paper corresponds to rupture plane of the earthquake which supposedly triggered the ecological catastrophe – disastrous landslide near the city of Stebnyk on 29.09.2017 at approximately 21h47m0.0s.

1. Geological maps of the western regions of Ukraine on sections - 3000, - 5000, - 7000 m. (1979). Ed. V.V. Glushko. Kyiv: Mingeo USSR. (in Russian).
2. Hlushko, V. V., Kuzovenko, V. V., Shlapynskyi, V. E. (2007). Geological Map of Ukrainian Carpathians, scale 1: 100000. Transcarpathian, Ivano-Frankivsk, Lviv, Chernivtsi region of Ukraine]. Ed. Yu.Z. Krupskyi. Report of JSC "Nadra Concern". Kyiv: Fund JSC "Nadra Concern" (in Ukrainian).
3. Hnylko, O. M. (2011). Tectonic zoning of the Carpathians in terms of the Terrane tectonics. Sections 1. Main units of the Carpathian building. Geodynamics, 2 (11), 170–172 (in Ukrainian).
4. Malytskyi, D. (2010). Analytic-Numerical Approaches to the Calculation of Seismic Moment Tensor as a Function of Time. Geoinformatic, 1, 79–86 (in Ukrainian).
5. Malytskyy, D. V. (2016). Mathematical Modeling in the problems of seismology. Kyiv: Naukova dumka Publ., (in Ukrainian).
6. Malytskyi, D. V., Hrytsai, O. D. (2017). Application of dynamic approaches for determination of focal mechanisms of earthquake in the Carpathian region. Proceedings of Scientific conference-seminar Seismological and geophysical research in seismically active regions is devoted to the memory of T.Z. Verbitsky and Yu. T. Verbitsky, Upper Synovid, June 1-2, 2017. Lviv: Spolom, 166–168 (in Ukrainian).
7. Malytskyy, D., Pavlova, A., Grytsai, O., Astashkina, O., Obidina, O. O., Makhnitskyy, M. P., Kozlovskyy, E. (2017). Models of Seismic Sources. Geoinformatika, 2, 14–23 (in Ukrainian).
8. Molotkov, L. A. (2001). Investigation of wave propagation in porous and fractured media based on effective models of Bio and layered media. Sankt-Peterburg: Nauka Publ. (in Russian).
9. Molotkov, L. A. (1984). Matrix method in the theory of wave propagation in layered elastic and liquid media. Leningrad: Nauka Publ. (in Russian).
10. Tectonic map of the Ukrainian Carpathians, scale 1: 200000. (1986). Ed. V. V. Glushko, S. S. Kruglov. Kyiv: Mingeo USSR. (in Russian).
11. Aki, K., Richards, P.G. (2002). Quantitative seismology, 2nd edn. Sausalito, California: University Science books.
12. Alekseev, A. S., Mikhailenko, B. G. (1980). The solution of dynamic problems of elastic wave propagation in inhomogeneous media by a combination of partial separation of variables and finite-difference method. J. Geophys, 48, 161–172.
13. Ben-Menahem, A., Singh, S.J. (1981). Seismic Waves and Sources. New York:Springer.
14. Bouchon, M. (1981). A simple method to calculate Green's functions for elastic layered media. Bull. Seismol. Soc. Am. 71, 959–971.
15. Chapman, C. H. (1957). A new method for computing synthetic seismograms. Geophysical Journal International, 54(3), 481–518.
16. Cormier, V. P., Richards, P. G. (1977). Full wave theory applied to a discontinuous velocity increase: The inner core boundary. J. Geophys., 43, 3–31.
17. Csontos, L., Vörös, A. (2004). Mesozoic plate tectonic reconstruction of the Carpathian region. Palaeogeography, Palaeoclimatology, Palaeoecology, 210(1), 1–56.
18. D'Amico, S. (2014). Source Parameters Related to a Small Earthquake Swarm Off-Shore of Malta (Central Mediterranean). Development in Earth Science. 2, 8–13.
19. Dziewonski, A. M, Chou, T. A., Woodhouse, J. H. (1981). Determination of earthquake source parameters from waveform data for studies of regional and global seismicity. Journal of Geophysical Research: Solid Earth, 86(B4), 2825–2852.
20. Fuchs, K., Muller, G. (1971). Computation of synthetic seismograms with the reflectivity method and comparison with observations. Geophysical Journal International., 23(4), 417–433.
21. Godano, M., Bardainne, T., Regnier, M., Deschamps A. (2011). Moment tensor determination by nonlinear inversion of amplitudes. Bulletin of the Seismological Society of America., 101, 366–378.
22. Hardebeck, J. L., Shearer, P. M. (2003). Using S/P amplitude ratios to constrain the focal mechanisms of small earthquakes. Bulletin of the Seismological Society of America, 93, 2432–2444.
23. Kennett, B. L. N. (1972). Seismic waves in laterally inhomogeneous media. Geophysical Journal International, 27, 301–325.
24. Kennett, B. L. N. (2002). The Seismic Wavefield 1, 2. UK: Cambridge University Press.
25. Kikuchi, M., Kanamori, H. (1991). Inversion of complex body waves-III. Bulletin of the Seismological Society of America, 81, 2335–2350.
26. Malytskyy, D., Kozlovskyy, E. (2014). Seismic waves in layered media. Journal of Earth Science and Engineering, 4, 311–325.
27. Miller, A. D., Julian, B. R., Foulger, G. R. (1998). Three-dimensional seismic structure and moment tensors of non-double-couple earthquakes at the Hengill-Grensdalur volcanic complex, Iceland. Geophysical Journal International, 133(2), 309–325.
28. Muller, G. (1985). The reflectivity method: A tutorial. J. Geophys., 58, 153–174.
29. Nakapelukh, M., Bubniak, I., Yegorova, T., Murovskaya, A., Gintov, O., Shlapinskyi, V., Vikhot, Yu. (2017). Balanced geological cross-section of the outer Ukrainian Carpathians along the pancake profile. Journal of Geodynamics, 108, 13–25
30. Sileny, J., Panza, G. F., Campus, P. (1992). Waveform inversion for point source moment tensor retrieval with variable hypocentral depth and structural model. Geophysical Journal International, 109(2), 259–274.
31. Sipkin, S. A. (1986). Estimation of earthquake source parameters by the inversion of waveform data: Global seismicity, 1981-1983. Bull.seism. Soc.A Bulletin of the Seismological Society of America, 76, 1515–1541.
32. Vavrychuk, V., Kuhn, D. (2012). Moment tensor inversion of waveforms: a two- step time frequency approach. Geophysical Journal International, 190(3), 1761–1776.
33. Wiggins, R. A., Helmberger, D. V. (1974). Synthetic seismogram computation by expansion in generalized rays. Geophysical Journal International, 37(1), 73–90.