Abstract. Numerical simulation of seismoacoustic emission (SAE) associated with fracturing in zones of shear stress concentration shows that SAE signals are polarized along the stress direction. The proposed polarization methodology for monitoring of slope stability makes use of three-component recording of the microseismic field on a slope in order to pick the signals of slope processes by filtering and polarization analysis. Slope activity is indicated by rather strong roughly horizontal polarization of the respective portion of the field in the direction of slope dip. The methodology was tested in microseismic observations on a landslide slope in the Northern Tien-Shan (Kyrgyzstan).

Abstract:The paper presents the results of deep seismic studies on Geophysical Reference Profile 1-SB (Sredneargunsk -Ust-Karenga -Taksimo -Vitim) in East Transbaikalia, Russia. The 1200 km long profile crosses the major tectonic structures of the Central Asian fold belt: the Argun median massif, the Selenga-Stanovoy and Transbaikalia folded regions, and the Baikal rift zone. Its northwestern fragment extends into the Angara-Lena monocline of the Siberian platform. The southeastern (Transbaikalia) and northwestern (Baikal-Patom) fragments of the profile are based on the spot (differential) seismic sounding technique using explosions and 40-tonne vibrators. The southeastern (Transbaikalia) fragment shows small crustal thickness values (~40 km), an almost horizontal position of the Moho, and high velocities of longitudinal waves (~8.4 km/sec) beneath the Moho. The analysis of parallelism graphs and the dynamic expression of the wave refracted from the Moho suggests a less than 5-10 km thick layer of high velocities and low gradients below Moho. The database on the territory of Transbaikalia includes ~200 wave arrival times from large earthquakes, which were refracted at the Moho at distances of ~200-1400 km. As part of the tomographic interpretation, using additional DSS data on the Moho, the territory of Transbaikalia has been mapped to show the patterns of the threshold velocity values at the Moho. The seismic data was used to contour an area with high velocity values in the mantle in the central part of the Mongolia-Okhotsk orogenic belt and the neighboring fold structures of Transbaikalia. According to the analysis of the seismic and geologic data on the study area, the mantle layer with high velocity values in the Mongolian-Okhotsk orogenic belt may be represented by the eclogitic rock plates.Key words: deep seismic sounding (DSS); velocity of longitudinal waves; hodographs from explosions and earthquakes; Moho; Mongolia-Okhotsk orogenic belt For citation : Soloviev V.M., Chechelnitsky V.V., Salnikov A.S., Seleznev V.S., Liseikin A.V., Galyova N.A., 2017. Specific velocity structure of the upper mantle in the Transbaikalia segment of the Mongolia-Okhotsk orogenic belt. GEODYNAMICS & TECTONOPHYSICS P U B L I S H E D B Y T H E I N S T I T U T E O F T H E E A R T H ' S C R U S T S I B E R I A N B R A N C H O F R U S S I A N A C A D E M Y O F S C I E N C E

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The paper describes the effects of the passage of the Chelyabinsk meteoroid (which exploded on 15 February 2013 over the Chelyabinsk Region), which were established from geophysical data from West Siberian stations. The trajectory and speed of the meteoric body from the start of the glow to the breakup were recorded by surveillance cameras and dashcams. Records from broadband seismic stations were used to determine the exact time of the explosion (03:20:34 UTC) from the arrival times of the surface wave produced by this event. The explosion energy was estimated from the surface-wave amplitudes at ~100 kilotons on the assumption that the wave originated from a point source similar to a high-altitude thermonuclear explosion. A database of records from seismic stations obtained during the meteoroid passage has been compiled.

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ON THE SAYANO-SHUSHENSK HYDRO POWER PLANT UDC 621.51:534 V. B. Kurzin and V. S. Seleznev It is demonstrated that the level of vibrations of turbines on the Sayano-Shushensk hydro power plant is enhanced by the capability of a compressible fluid to perform its own hydroacoustic oscillations (which can be unstable) in the turbine duct. Based on the previously obtained results of solving the problem of natural hydroacoustic oscillations in the turbine duct and some ideas about turbine interaction with an unsteady compressible fluid flow, results of full-scale studies of turbine vibrations and seismic monitoring of the dam of the Sayano-Shushensk hydro power plant before and during the accident are analyzed.Introduction. Various possible reasons were given after the accident on the Sayano-Shushensk hydro power plant (HPP), which happened on August 17, 2009. These reasons were analyzed in much detail in [1]. Some versions of the accident are based on the assumption that the turbine was subjected to a certain pulsed high-power action (something like a hydraulic hammer), which exceeded the safety margin of the structure. These versions, however, do not agree with the results of seismic monitoring of the dam of the Sayano-Shushensk HPP before and during the accident. The main reason for the accident is assumed to be the fatigue failure of the fixtures of the turbine cover of the power-generating unit No. 2, which was induced by the high level of turbine vibrations in the standard operation mode. This fact was established by the technical commission investigating the reasons for the accident.The elevated level of turbine vibrations on the Sayano-Shushensk HPP (as compared with vibrations obtained for its model) was observed in full-scale tests performed back in 1988. It was shown [2, 3] that emergence of such vibrations is caused by the effect of water compressibility on turbine interaction with the unsteady flow, which was ignored in design of the Sayano-Shushensk HPP. The study of this problem was continued in [4,5]. Based on results of these studies, certain restrictions were imposed on operation of power-generating units of the Sayano-Shushensk HPP. It should be noted, however, that the hydrodynamic problem in [4,5] (results of these studies were used as a basis for the version described in [1]) was considered in a linear formulation and in a quasi-steady approximation. It is convenient to use the solution of this problem in such a formulation for engineering calculations, but the solution is rather rough and does not explain some qualitative features observed in experiments. In addition, there is a mistake in [4,5].In the present work, based on the theory of cascades in an unsteady flow [6-8] and on the laws of aeroacoustics, we study the qualitative effect of nonlinearity and reduced frequency of vibrations on turbine interaction with an unsteady compressible fluid flow, which was partly taken into account in [2, 3], but skipped in [4,5]. Using the data obtained, we analyze the results of full-scale studies of turbi...

Analysis of geological and geophysical data on the boundary zones between the Eurasian plate and other plates shows poor knowledge of the deep structure of the region. This information will help to refine the position of the plate boundaries and the structure of the Earth’s crust and mantle. We present data on the seismicity and deep structure along the deep seismic sounding (DSS) profile running across the boundary between the Eurasian and Okhotsk plates. A comprehensive analysis of the DSS materials and seismic data shows a significant expression of this boundary zone both in the deep Earth’s crust structures and in the Moho. A zone of anomalous seismicity and deep structure extends along the DSS profile for several hundred kilometers. We have refined the position of the main boundary between the Eurasian and Okhotsk plates, which passes approximately along 144° E.

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