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Russian Geology and Geophysics

2016 year, number 3


Yu.L. Rebetsky1, N.A. Sycheva2, V.N. Sychev2, S.I. Kuzikov2, A.V. Marinin1
1Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, ul. B.Gruzinskaya 10, Moscow, 123995 Russia
2Scientific Station of the Russian Academy of Sciences, Bishkek 49, Bishkek, 720042, Kyrgyzstan
Keywords: Тектонические напряжения, механизмы очагов землетрясений, геодинамический режим, внутриконтинентальный ороген, Tectonic stresses, earthquake focal mechanisms, geodynamic regime, intracontinental orogen


In this study we present a detailed analysis of natural stresses in the Northern Tien Shan crust averaged in a window of 10-15 km obtained from seismological data of the local KNET network. The transformation of focal mechanism data into the parameters of the stress tensor was based on the method of cataclastic analysis of rupture dislocations elaborated by Yu.L. Rebetsky (Institute of Physic of the Earth, Moscow). The results, including the orientation of the principal stress axes and the reduced stresses, are presented for four depth layers. It was shown that the central part of the study area is dominated by horizontal compression, while multiple domains characterized by horizontal shear and superimposed compression or pure horizontal shear are also present (uppermost layers in the eastern part of the Chuya depression, Suusamyr depression and adjoining regions, in the central part of the Kyrgyz Range). There are also several large domains of high and low effective confining pressure, which defines the corresponding deviator stress, according to the Coulomb-Mohr law. It was shown that relatively strong earthquakes are correlated with zones with low levels of effective pressure where the ruptures are characterized by lower resistance to brittle fracturing, i.e., Coulomb friction stresses. It was also shown that a distinct segment of the ~60 km E-W striking fault on the northern slope of the Kyrgyz Range generates a uniform distribution of stresses, corresponding to a dextral slip along of its edges.