On the problem of deep earthquakes in the Crimean-Black Sea region

 

V.Yu. Burmin¹, L.A. Shumlyanskaya²

 

¹Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia

 

²Institute of Geophysics, National Academy of Sciences of Ukraine, Kiev, Ukraine

 

Corresponding author: Valery Yu. Burmin, e-mail: burmin@ifz.ru

 

Abstract. It is generally accepted that only crustal earthquakes can occur in the Crimean-Black Sea region. Since the problem of the deep earthquakes in the Crimean-Black Sea region is extremely important for constructing a geodynamic model of this region, we attempt to verify the validity of this common point of view. For this purpose, the coordinates of all the earthquakes registered by the stations of the Crimean seismological network were reinterpreted with the algorithm developed by one of the authors. For our analysis, we used the data published in seismological catalogs and bulletins of the Crimean-Black Sea region for 1970–2012. To refine the coordinates of the hypocenters of earthquakes in the Crimean-Black Sea region, in addition to these stations of the Crimean seismological network, additional information was used by seismic stations located on the coast around the Black Sea. In total, 61 seismic stations were used to determine the hypocenter coordinates. The used earthquake catalogs for 1970–2012 contain information on 2140 events of magnitude from -1.5 to 5.5. The bulletins provide information on the arrival times of P- and S-waves at seismic stations for 1988 events recorded by three or more stations. The principal innovation of the present study is the use of the original author’s hypocenter determination algorithm based on minimizing the distance functional between the points (X, Y, H) and (x, y, h) corresponding to the theoretical and observed seismic wave travel times from the earthquake source to the recording stations. The determination of the coordinates of earthquake hypocenters in this case is much more stable than with the usual minimization of the functional for earthquake travel time residuals. Since the determination of the hypocenter coordinates can be influenced by the seismic velocity structure under each station, special attention was paid to the collection of information on velocity sections. To assess the effect on the results of the calculation of the velocity model of the upper mantle, two different models were used: low velocity and high velocity, the results obtained were compared with each other. Both these models were set to a depth of 640 km, which is of fundamental importance in determining hypocenters of deep earthquakes. As a result of the carried out studies of the Crimean-Black Sea region we have revealed more than 70 earthquakes with a depth of more than 60 km. The reality of the obtained depths is confirmed by the comparison results of the initial experimental data from the bulletins used with the theoretical hodographs for earthquake sources with a depth of 50 and 200 km. The revealed deep earthquakes in the Crimean-Black Sea region significantly change our understanding of the structure and geotectonics of this region.

 

Keywords: hypocenter, earthquakes, deep earthquakes, Crimea, Black Sea.

 

 

About the authors

 

BURMIN Valery Yurievich — Dr. of Ph. & Math, chief research scientist, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. 123242, Moscow, ul. Bolshaya Gruzinskaya 10, stroenie 1. Tel.: +7 (499) 254-68-95. E-mail: burmin@ifz.ru

 

SHUMLYANSKAYA Lyudmila Aleksandrovna — Ph. D. in Geological Sciences, scientific reseacher, Institute of Geophysics of NAS of Ukraine. Ukraine, 03860, Kiev, Palladina Avenue 32. Tel.: +3 (8093) 146-50-12. E-mail: lashum@ukr.net

 

Cite this article as: Burmin V.Yu., Shumlyanskaya L.A. On the problem of deep earthquake in the Crimean-Black Sea region, Voprosy Inzhenernoi Seismologii (Problems of Engineering Seismology). 2017. Vol. 44, No. 3, pp. 83–94. DOI: 10.21455/VIS2017.3-5 [in Russian].

 

English translation of the article will be published in Seismic Instruments, ISSN: 0747-9239 (Print) 1934-7871 (Online), https://link.springer.com/journal/11990), 2018, Volume 54, Issue 3.