Seismicity and the stressed state of the starobin potassium salt deposit in Belarus

: pp. 88-95
Received: December 09, 2013
Centre of Geophysical Monitoring, National Academy of Sciences of Belarus
Centre of Geophysical Monitoring, National Academy of Sciences of Belarus
Institute of Physics of the Earth of the Russian Academy of Sciences
Centre of Geophysical Monitoring, National Academy of Sciences of Belarus
Centre of Geophysical Monitoring, National Academy of Sciences of Belarus

Purpose. To carry out the investigations in the the East European Platform southwest with a special emphasize made on the Soligorsk region, where the Starobin deposit of potassium salts of the Late-Devonian age is located. The interest of scientists to just this region is explained by the fact that a swarm of crustal earthquake foci is restricted within this deposit area, which is in marked contrast to other seismic events that are few and far between and rather evenly distributed over the other territory of Belarus. Methods. The stressed state was reconstructed for the studied region using methods: seismotectonic method with the use of data of earthquake source mechanisms; tectonophysical method, based on the analysis of geometry of Mesozoic-Cenozoic sedimentary rock fracturing. Changes of the environment stressed state as a result of rock extraction and redistribution served as a mechanism triggering a swarm of earthquakes at Boundaries of rather large tectonic blocks in deep fault zones located within the deposit region. Results. A team of the Russian and Belarusian scientists undertook some years ago joint geodynamic investigations for the project entitled “Study of the lithosphere stressed state and seismicity in the East European Platform (EEP) southwest” under financial backing of the Russian and Belarusian Funds of Fundamental Investigations. Some of the results obtained were already reported [Belousov et al., 2006a, 2006b; Aronov et al., 2009]. The investigations was carried out in the western part of East European platform with a special emphasize made on the Soligorsk region, where the Starobin deposit of potassium salts of the Late-Devonian age (D3 fm, Famennian stage) is located. The fact of local seismicity instrumentally recorded in the Starobin deposit region against a total absence of seismic events for several last decades over the most part of Belarus suggests the recent activation of faults in the Soligorsk region. Scientific novelty and practical significance. The stressed state of the geological environment caused by the rock extraction and deposition has been continuously changed and can be obviously a reason to suggest the induced nature of earthquakes observed. Seismotectonic deformations in the studied region are found to be well correlated with numerous disjunctive deformations manifested at the most recent stage of evolution. The seismotectonic environment of shear deformation with evidences of submeridional compression and, respectively, sublatitudional extension appears to be typical of the northwestern part of the Pripyat Trough. Beginning from the Late Pleistocene till the present the maximum compressional axis has been oriented NNW, that was determined from the earthquake source mechanisms. The investigations performed showed some evidences of a considerable activation, which had occurred in the deposit region in the Late Cenozoic, when the velocity of vertical movements increased and their direction changed in some faults. Amplitudes of slip in these faults were as high as 30 m and more for the last 25-28 million years.

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