—This work is devoted to the development of the engineering seismic monitoring method created in Geophysical Survey of the Russian Academy of Sciences (GS RAS). In previous years, the “method of standing waves” was created and put into practice. It helps to separate natural oscillation modes of buildings and other engineering structures. The natural oscillations of hundreds of various objects (buildings, bridges, dams, etc.) had been studied and identified. We assumed that the physical condition of studied constructions could be controlled during exploitation by measuring the changes of natural oscillation frequencies. That would help to identify the appearance of defects in constructions, to prevent the risk of their destruction. However, it turned out that not everything is that simple: changes in frequency values are logically affected by changes in the environment around the studied objects. This article provides examples of these relations, influence of changes in environmental temperature, mass of objects and precipitation on the frequencies of natural oscillations.

-Information on the distribution of earthquake hypocenters for many seismically active zones of Siberia remains insufficient, which is associated with sparse networks of seismological observations. The paper presents the results of determining the earthquake depths in several seismogenic areas in the Altai-Sayan region, Cisbaikalia, Transbaikalia, and Yakutia using the travel time of longitudinal refracted waves from the Mohorovi & ccaron;i & ccaron; discontinuity (Pn waves) from earthquakes and the recently obtained information about the deep structure of these regions. The depth determination algorithm is tested using data from aftershocks of large earthquakes occurring in Tuva in 2011 and 2012 (ML = 6.7 and 6.8), recorded both by the regional seismological network and by a local group of seismic stations. Different methods are applied to reveal that some aftershock depths have a close match, including those for the main shocks - the Tuva-1 and Tuva-2 earthquakes. Another good match of earthquake depths is obtained using & Rcy;n waves with materials from regional and detailed studies of the Baikal branch of the Geophysical Survey of the Russian Academy of Sciences in the Muyakan activation site in the Baikal rift zone. The resulting data complement the information on the hypocenter of the main shock and confirm the change of the Muyakan activation cluster from large depths to shallow ones since the onset of activation in 2014. New information on the earthquake depths using & Rcy;n waves is obtained in Yakutia along the border of the largest Eurasian and Okhotsk tectonic plates. It is revealed that they decrease to 6-12 km as compared to higher depths of 20-30 km in adjacent areas. The resulting series of new information on the distribution of earthquake hypocenters using & Rcy;n waves is extremely important mostly because it indicates the possibility of identifying and redefining earthquake hypocenters using previous seismological observations in seismically active zones of Siberia.

The paper presents analysis of the seismicity and deep structure of the Trans-Baikal region in the section of the reference geophysical profile 1-SB. It was determined that the Earth’s crust and upper mantle has a complex heterogeneous structure. The thickness of the Earth’s crust varies from 40 km in the South-Eastern part of the profile and in the areas of intermountain depressions in the North-Western part, and up to 48 km in the areas of mountain ranges. The values of the boundary velocities along the M boundary also vary greatly, from higher values of 8.4‒8.5 km/s for P-waves and 4.9‒4.95 km/s for S-waves (especially in the South-Eastern part of the profile) to reduced values of 7.8‒8.0 km/s for P-waves and 4.6‒4.7 km/s for S-waves in the section of the Baikal rift zone in the North-Western part of the profile. A strong inhomogeneous structure of the medium in terms of elastic wave velocities, Vp/Vs velocity ratios, and the Poisson’s ratio is determined for the upper and the middle crust at depths of 8‒20 km. The authors determined that zones of increased seismicity are referred to blocks of the Earth’s crust with inhomogeneous velocity structure according to data of differently polarized P- and S-waves. The area of the Baikal rift zone, in the immediate vicinity of the largest Muya earthquake of 1957 with M = 7.6, is characterized by elevated inhomogeneity in the upper part of the Earth’s crust according to the elastic wave velocities and secondary parameters of the medium (Vp/Vs ratio, K* = = Vp/(γ – 1), where γ = Vp/Vs, Poisson’s ratio (σ)). A number of other inhomogeneous deep zones have also been identified in the profile based on anomalies of P- and S-waves velocities and secondary parameters of the medium, which correlate to varying degrees with seismically active sites according to long-term instrumental observations. The established unambiguous connection of large inhomogeneous zones of the upper crust of the Trans-Baikal region with the accumulation of stresses and their discharge in the form of strong earthquakes allows us to make a reasonable medium-term forecast of catastrophic events.

This study is concerned with an analysis of seismicity and deep structure in the Transbaikalia along the 1-SB reference geophysical traverse. We have found a complex inhomogeneous structure of the crust and upper mantle. The crustal thickness varies between 40 km in the southeastern part of the traverse and in intermontane troughs in its northwestern part on the one hand and 48 km in mountain ranges. Strong variation also affects boundary velocities at the Moho, ranging from 8.4‒8.5 km/s for compressional waves and 4.9‒4.95 km/s for shear waves (especially in the southeastern part of the traverse) to lower values of 7.8‒8.0 km/s for compressional waves and 4.6‒4.7 km/s for shear waves in the area of the Baikal Rift Zone in the northwestern part of the traverse. A strongly inhomogeneous earth structure based on elastic wave velocities, Vp/Vs velocity ratios, and Poisson’s ratio was found for upper and middle crust at depths of 8‒20 km. It was also found that zones of higher seismicity tend to coincide with crustal blocks with inhomogeneous velocity structure based on differently polarized compressional and shear waves. Higher inhomogeneity in upper crust as inferred from elastic wave velocities and secondary earth parameters (Vp/Vs velocity ratios, the parameter K* = Vp/(γ ‒ 1), where γ = Vp/Vs, and Poisson’s ratio (σ)) characterize the area of the Baikal Rift Zone in an immediate vicinity of the great Muya earthquake of 1957 with М = 7.6. As well, several other deep zones of inhomogeneity have been identified along the traverse line based on anomalies of Р and S velocities and secondary earth parameters that correlate to varying degrees with seismically active areas based on multiyear instrumental observations. We have identified an unambiguous relationship of large inhomogeneous zones in the Transbaikalia crust with stress buildup and stress release in the shape of large earthquakes, thus substantiating the intermediate-term prediction of catastrophic events.

on the analysis of the 2017-2021 recordings from the Kharino seismic station (the Altai-Sayan seismic stations network) and the 2002-2019 satellite imagery, the trigger of the July 18, 2020 earth-slide at Elbashinsky waste rock dump of the Kolyvan Anthracite Deposit (Novosibirsk region) has been established. The study of natural oscillations of the mine waste dump allowed estimating its stability and thus contributing to environmental and industrial safety in surface mining of solid minerals.

The relationship between temperature fluctuations and changes in natural frequencies of a piletype engineering structure located on permafrost soils is investigated in connection with the development of methods for monitoring the technical condition of similar structures. The object of the study is the Palace of Culture of the polar branch of PJSC MMC Norilsk Nickel, located in Norilsk, where in recent years the thawing of the soils has a potential threat to the stability of engineering structures. The basic values of the frequencies of natural oscillations of the building were determined in August 2021 by the method of coherent reconstruction of the fields of standing waves and are 3.0, 3.7, 4.7 Hz on the short axis and 3.5 and 5.2 Hz on the long axis. The current (daily) frequency values are determined with an error of no more than 0.01 Hz from the amplitude spectra of seismic noise recordings (without active sources), which were obtained during continuous seismic monitoring from the end of August 2021 to the beginning of September 2022. From comparing the changes in the frequencies of natural oscillations with fluctuations in ambient temperature, it follows that during the year the frequencies change significantly (in winter their values are 11–12% higher than in summer), presumably due to defrosting/ freezing of the upper part of the soil. Against the background of this change, local fluctuations in frequency values were revealed due to cooling/ heating of the material of the building mainly at a positive ambient temperature (frequencies increase in direct proportion to temperature within 5–7%). According to the analysis of monitoring data after the annual cycle, the natural frequencies of the building in August 2021 and 2022 are not equal (the difference is up to 1.7%), which is presumably explained by the different depth of ground defrosting in the summer. To assess the impact of this phenomenon on the technical condition of the building, it is necessary to continue monitoring, first of all, to obtain data on changes in the natural frequ

—A river seismic survey technology based on using pneumatic water sources and autonomous seismic recorders, which are installed on the river bank and configured for continuous seismic recording, is developed at the Geophysical Survey of the Russian Academy of Sciences (GS RAS). In recent years, several thousand kilometers of profiles have been developed by the CDP-2D method on the rivers of East Siberia: Lena, Nizhnyaya Tunguska, and Vitim. Previously, only 6- to 10-s seismograms were used to study the structure of the upper part of the Earth’s crust. At the same time, the deep structure of the crust in the vast territories of East Siberia remains poorly understood because of the high cost of research. The river seismic survey data are used on a profile section acquired in the lower reaches of the Lena River to demonstrate the possibility of studying the crustal structure to the full depth, including the Mohorovičić discontinuity. For this purpose, the archival seismic records are reprocessed with the construction of montages of seismograms of increased duration (up to 23 s). The low-amplitude oscillations of reflected waves from deep boundaries are distinguished owing to multiple summation, which is much larger than in conventional seismic surveys. The equipment used in this study has a sufficient dynamic range, and a high multiplicity is achieved by increasing the binning area. Wind noise leads to the inferior quality of time sections of the upper crust but does not worsen the section at great depths, so this material should not be excluded from processing. The river seismic surveys carried out using the technology developed at the GS RAS on the rivers of East Siberia within about 2700 km contain data that make it possible to build deep sections down to the Mohorovičić discontinuity, and this work needs to be done.

Based on the spectral analysis of low-amplitude seismic signals records (continuous monitoring data for 2001-2021) from one of the stations of the seismological network located at a distance of 4.4 km from the Sayano-Shushenskaya HPP, a method for determining the daily values of natural oscillation frequencies of constructions has been developed (the frequencies of the first seven modes are identified with an error no more than 0.01 Hz). The results of processing and analysis of unique data indicate a continuous and non–slowing increase in the values of the natural oscillation frequencies of the dam in the range of 0.02-0.05 Hz during the observation period. This is explained either by silting up the bottom of the reservoir in the area adjacent to the dam, or by adapting the dam and its base with subsequent increase in mechanical rigidity of the construction. At the same time, the intervals are analyzed at which the influence of seasonal environmental influences on the construction is insignificant (summer-autumn period, the water level in the reservoir is close to the maximum). The developed method of identification of natural oscillation frequencies of constructions from low-amplitude seismic signals is intended to monitor their technical condition, in order to prevent the risks of destruction of dams, industrial structures, infrastructure facilities and civil buildings with a high degree of reliability and is economically profitable in comparison with known solutions.

According to the data of the seismic station «Cheryomushki», resonance frequencies of the Sayano-Shushenskaya HPP dam and their continuous changes over 20 years are calculated. Seasonal changes in the values of resonance frequencies, which correlate with the level of the reservoir, as well as long-term (global) changes associated with the consolidation of the dam body, are highlighted.

Buildings and structures are objects of increased responsibility. Under certain conditions, they are subject to negative impacts caused by the impact of various natural and man-made factors on them. It is necessary to monitor both the technical condition of the object and the dynamic influences acting on it, possibly carrying danger both for the structure and for its parts. SEF USGS RAS has developed a method for continuous monitoring of the physical condition of structures, which allows determining the values of natural frequencies of structures from records of a continuously recording seismic station and, if significant deviations from their initial values are detected, drawing conclusions about the condition of structures. reasons for changing the dynamic state of the structure. This study will show the results of such work within the framework of the infrastructure of the Akademgorodok of Novosibirsk, where the results of observations of the natural oscillation frequencies of several residential buildings are presented. During the observations, the influence of external temperature on them was revealed - an increase in ambient temperature leads to an increase in the values of the frequency of natural oscillations, and a decrease in temperature leads to a decrease in values. The greatest change in the frequency of natural vibrations of buildings occurs in summer, at temperatures above 30 degrees C, when there is a great contrast between daytime and nighttime temperatures.

The possibility of using river seismic data for oil and gas exploration to study the deep structure of the Earth's crust is shown. This method uses water seismic source points and bank-mounted autonomous seismic recorders installed for continuous seismic recording. About 2700 km of seismic profiles were completed by the CDP-2D method along the rivers of Eastern Siberia (Lena, Nizhnyaya Tunguska, and Vitim). The structure of the upper part of the Earth's crust (up to several kilometers) has been studied, while its deep structure remains unknown. It is shown that the materials of seismic river surveys carried out along a 60-km section of the profile in the lower reaches of the Lena River, using the method developed by the Geophysical Survey, Russian Academy of Sciences, contain data allowing us to construct cross sections throughout the thickness of the Earth's crust up to the Moho boundary. Low-amplitude fluctuations of reflected waves from deep boundaries are distinguished due to the wide dynamic range of the devices used and the multiple summation, which is significantly higher than in the case of the traditional seismic surveys. The high multiplicity is achieved by reducing the distance between blast points, increasing the sounding bases and the binning area.

The article presents possibility of determining deep structure of the Earth`s crust by low-amplitude signals of longitudinal reflected waves at times up to 14-15 s due to wide dynamic range of the using equipment and multiple summation up to 2500. The conclusion is based on the results of long-duration (up to 23 s) seismograms analysis, carried out after reprocessing of the archival materials of river seismic profiling by the CDP-2D method in a 60-kilometer section in the lower part of the Lena river in 2018, exactly it was the materials of continuous ground-based registration of seismic oscillations by "Baikal" equipment from "Malysh" water pneumatic sources. High multiplicity is obtained by reducing the distance between shot points, adding source-receiver distances and increasing bin size. In the Eastern Siberia more than 2700 km of profiles were carried out using similar technologies; it allows to identify structure of the Earth's crust of the areas, which have not been studied by deep seismic methods previously.

This paper reports the results of satellite image and seismological data analysis obtained when considering the causes of a landslide on the Yelbashinskii dump at the Kolyvan anthracite deposit. The potential for determining the natural vibrations of large objects from low-frequency seismological records and monitoring thereof has been demonstrated.

The article presents a method for monitoring the natural frequencies of HPP dams according to continuous seismic observations. The object of the research is the largest arched dam in Russia, the Chirkey HPP located in the Caucasus. If damaged, it could cause great loss of property and human life, but disasters can be minimized by using effective dam structural health monitoring. The study for changes in the natural frequencies of engineering structures is one of the most common methods of remote control over their structural health. However, the determination of values of natural frequencies of huge concrete dams is a very difficult procedure due to their have complex construction. Moreover, interpretation of changes in the natural frequencies values is difficult due to the significant influence of the water level in the reservoir. Consequently, at the initial stage, we performed a detailed study of the natural oscillations of the dam using the method of coherent restoration of the standing wave fields with the definition of both the natural frequencies of the structure and their modes. They were conducted twice at the minimum and maximum upstream level and for the first time highlighted the features of seasonal changes in the full field of standing waves. The normal modes were determined that are present in oscillations at different upstream levels and which frequencies can be detected continuously from the records of seismic equipment. The series of frequency changes during the year are calculated. For the first time we established that, frequency changes are by 5 to 11 days behind reservoir level changes and assumed that relaxation processes of the dam body and / or its base cause the delay after the upstream level changes. We calculated dependencies for predicting the frequency values from the reservoir level, taking into account the delay time. As a result, we proposed an approach for monitoring of the dam structural health based on a comparison of the observed natural frequencies with the predicted ones. The developed method can be applied to monitor the structural health of concrete dams of other HPPs.