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This article presents the results of mapping a karst cave by the passive seismic standing waves method. Barsukovskaya cave is located about 100 km southeast of the city of Novosibirsk (Russia). The total length of the cave's passages and grottoes is estimated at about 200 m, the maximum depth from the earth's surface is about 19 m. The method for studying underground cavities used is based on the effect of the generation of standing waves by microtremor in the space between the earth's surface and the cave roof. The accumulation of amplitude spectra of a large number of microtremor records makes it possible to determine the frequencies of the first few modes of these waves. Areal passive seismic survey on the earth's surface above the cave made it possible to construct a map of the lowest mode frequency distribution over the cave roof. Since no standing waves were observed at other points, this map reflects the cave structure in plan, which confirms the comparison with the cave diagram drawn up earlier by one of the speleologists. A schematic map of the depth of the cave roof was constructed using the longitudinal wave velocity V p = 3120 m/s determined by the rock samples selected near the entrance to the cave. This map at a qualitative level also agrees with the data of speleologists, which indicate that the cave, on average, gradually becomes deeper from the entrance to its dead-end branches. The shallower depths in comparison with the data of speleologists are apparently explained by a very low estimate of the velocity determined from a rock sample taken near the entrance to the cave. The reliability of the obtained cave mapping results is confirmed by the numerical simulation results using the finite-element method.

After a major accident in August 2009 at the Sayano‐Shushenskaya Hydroelectric Power Plant (SS HPP), all 10 hydroelectric units (HU) with a total capacity of 6400 MW failed. After investigating the causes of the accident and the reconstruction of the hydroelectric power plant, there was to develop a methodology for monitoring the operation of the newly commissioned HU. For inspection, a method was developed based on monitoring the natural frequencies of the dam structures and forced vibrations caused by the operation of the equipment. The article presents the main results of this study. Within the framework of the proposed approach, monitoring was carried out at various observation points of the dam structures and the turbine hall, as well as on a network of remote seismic stations. Based on the data recorded since 2009, an assessment of the parameters of dynamic impacts arising from the operation of hydraulic units of various types in different load modes on the elements of the HPP structure was carried out, and cause‐and‐effect relationships between changes in the operating modes of equipment and recorded vibrations in dam structures were investigated. An estimate of the general level of vibrations during the operation of various types of hydraulic units is given. As a result, the operating modes of hydraulic units are determined, in which there is a multiple increase in the amplitude of natural vibrations of the dam, an assessment of the operational characteristics of hydraulic units is given, taking into account the impact of seasonal conditions and changes in the water level in the reservoir.

To ensure the safe operation of roads, it is necessary to periodically monitor the condition of road surfaces. Lately, near-surface geophysics methods have been actively used to solve such problems. The seismoacoustic methods that are used to diagnose road surfaces are typically dynamic methods based on the excitation of body or surface elastic waves in the road surfaces. The purpose of this work is to assess the possibilities of using elastic standing waves for diagnosing a hard road surface. This article presents the results of field experiments that demonstrate the possibility of detecting cavities under an asphalt pavement using flexural standing waves. Such waves, like vibrations of a membrane fixed or partially fixed at its edges, can be formed on the hard surface cover above the cavity as a result of exposure to acoustic noise. In this article, the accumulation of amplitude spectra of a large number of noise records was used to extract standing waves from the acoustic noise recorded on the surface of the pavement. It is shown that the joint visualization of the averaged spectra obtained by profile observations over the cavity makes it possible to confidently identify several modes of flexural standing waves. Based on the areal measurements, a map of the distribution of the amplitudes of one of the modes of flexural standing waves in the asphalt pavement over the cavity was constructed. At a qualitative level, this distribution is consistent with the results of computer simulations using the finite element method. The fact that, under the influence of acoustic noise in the pavement, the flexural standing waves are formed which are absent at other places indicates the absence of rigid contact at its lower boundary. Thus, the horizontal dimensions of the cavity can be estimated from the size of the area on which flexural standing waves are formed. In addition, the article shows that the analysis of vertical compressional (but not flexural) standing waves arising in the pavement under the influence of noise allows us to investigate the thickness of the pavement and to qualitatively assess the ratio of acoustic stiffness of the pavement and the underlying layer.

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