Seismic Instruments最新文献

For a unique building in the form of a tower with a core of rigidity in the center, experimental studies of natural oscillations by the standing wave method with theoretical calculations based on a finite element model are performed and compared. From the experiment, ten translational horizontal modes of natural oscillations, five torsional modes of natural oscillations, and eight vertical modes of natural oscillations were identified and investigated. The finite element model is used to calculate the natural oscillations corresponding to all experimentally isolated oscillation modes. The experiment and theory are compared over the entire set of natural frequencies. Differences in natural frequencies reached 20%. After the studies, if possible, correction of the computational model ensured the difference between the experiment and the theory in terms of the values of natural frequencies of no more than 7.5%. Verification of design models of buildings using the standing wave method is an effective approach to assessing the physical condition of buildings and their seismic resistance.

The article presents the results of identifying correlation relationships between magnitudes of different types, calculated in international and regional seismological centers. An increase in the number of seismic stations in the Arctic in the 21st century and corresponding increase in the number of recorded earthquakes (due to a decrease in the threshold recording magnitude) has made it possible to identify quantitative relationships between magnitudes based on large samplings of earthquakes and in a wide range of magnitudes. From International Seismological Center data for 1995–2020, we obtained 30 ratios between magnitudes of different types, calculated at different seismological centers, in particular, magnitudes ranging from m_b and M_S 2.6 and M_L = 0.8. The identified relationships will make it possible to compile an aggregated unified catalog of earthquakes for certain regions of the Arctic, which is necessary, primarily, for assessing the seismic hazard of certain areas, as well as studying low-magnitude earthquakes and clusters and swarms of such quakes.

The paper presents the results of both theoretical and experimental studies carried out in the framework of the integrated problem on improving national systems for high-precision instrumental observations using the IPE RAS Geophysical Observatory in the Northern Caucasus. The geophysical observatory is located in the vicinity of the Mt. Elbrus in a deep underground tunnel of the Baksan Neutrino Observatory, supervised by INR RAS. Along with general information about the underground laboratory, the significant performance characteristics of the main instrument—a two-axial tiltmeter—are presented, as well as the data acquisition, processing, and storage system. The influence of natural and technogenic disturbances on the results of interpreting both tidal harmonics and other long-period variations are estimated via the developed technique to minimize the impact of a separate class of disturbances; an express estimate of the amplitude of the observed tide is performed.

The article discusses the advisability of conducting detailed macroseismic surveys within large cities and urban agglomerations. A retrospective analysis of information about earthquakes that occurred in the past decades and were felt in Irkutsk with an intensity of I = V or higher revealed the problem of preserving and availability of primary data on earthquake effects. Processing of the macroseismic data collected using internet-based questionnaires for the Irkutsk area after the September 21, 2020 Bystraya earthquake was carried out. The usage of online questionnaires has demonstrated high efficiency and information content, and also opened up certain possibilities such as improving the method with respect to the particular conditions of East Siberia. A large number of responses from earthquake eyewitnesses makes it possible to assess the shaking intensity separately in every administrative unit of Irkutsk, which in turn contributes to an increase in the detail of documenting the earthquake macroseismic field. The results allow us to consider assessment of the shaking intensity within certain parts of Irkutsk city as more rational versus assessment for the entire territory of the city.

Structural and geomorphological studies were carried out in the foothills of the Kurai Range in southeast Gorny Altai. It is shown that the structure of the Kurai Fault Zone here is governed by north-dipping reverse faults and thrusts, along which the Kurai Range thrusts onto deposits of the Chuya and Kurai depressions. They are feathered by south-dipping backthrusts. Displacements along these fault systems lead to growth of forbergs in front of the range front and separation of smaller negative morphostructures from the Chuya and Kurai depressions. Numerous fault scarps have been revealed along the faults, which are outlets of seismic sources of paleoearthquakes to the surface. For a number of scarps, in addition to the vertical component, the strike-slip component of displacements is also read in the relief. Some fault scarps have an age of a few hundred years and arose in the sources of paleoearthquakes with minimal magnitude: M_W = 6.7–7.3.

The efficiency of using microseisms for seismic microzoning (SMZ) is discussed based on experimental field data in different geological conditions. The microseism method is in the list of recommendations and codes and is widely used because of its low cost. In SMZ, microseisms are used to estimate the shaking intensity increment by calculating the amplitude spectra at seismic stations and resonance characteristics of ground layers, usually in combination with other methods. Difficulties in taking into account numerous local noise sources may significantly reduce the accuracy of the results. This has to be considered when planning field works for each object (site). In some cases (high anthropogenic noise level), it is better to refrain from using the spectral amplitude ratio in the high frequency band (above 3 Hz). Calculation of intensity increments individually in the 0.5–2 and 2–3 Hz bands, taking as the final increment the maximum of both calculations, guarantees the due level of conservatism; hence, the microseism method is also applicable to critical facilities. The spectral ratio of the horizontal and vertical components of seismic motion (H/V) can be used to estimate the resonance characteristics of soils and structure of the upper part of the soil profile, in particular, the depth of the soil/bedrock boundary.

A complex of dislocations is described (extended gently dipping faults with a displacement of up to 1 m, dipping towards the center of the lens, steep faults with displacements of 5–20 cm), liquefaction structures (angular pseudonodules of sands in silts), near fault and near-strike-slip fault folds in the section of a large lens of the Mikulinskiy lacustrine–bog sediments (interbedded silt with a horizon of peat and clayey gyttja) of the aseismic region of the Russian Plate (Klin–Dmitrov ridge) in order to compare them with similar structures of the Baltic Shield, the seismogenicity of which is being discussed. It has been shown that the sequence was not subjected to periglacial phenomena such as glaciotectonics, glaciokarst, cryogenic deformations, the presence of which and pseudomorphism along polygonal-veined ice was noted only in the roof of the Mikulinskiy interglacial complex. A model is proposed for the formation of dislocations as a result of slumping of a silt layer with uneven subsidence of the underlying layers of peat sediments, which have been strongly compacted during lithogenesis, which explains the features of the kinematics of faults. The results showed that the dislocations of the Mikulinsky complexes of the Dmitrov quarry do not fundamentally differ from similar structures of the Baltic Shield, which confirms their lithogenic or exogenic (rather than seismotectonic) genesis in both regions. The differences in the dislocation complexes of the two regions are in the different sequence of formation of liquefaction and faults structures: in the Dmitrov section, they were formed synchronously, in the sections of the Baltic Shield, asynchronously.

The method proposed by the authors makes it possible to determine the nature of changes in two components (intergranular and fracture) of the total porosity. Changes in the fracture and intergranular porosity were investigated during fracture nucleation of sandstone samples under modeling in situ conditions. Sandstone samples were held at constant confining and pore pressure modeling in situ conditions. At the same time, only a slight decrease in the total and intergranular porosity was observed. However, only in the sample with an initially large fracture porosity was an increase in fracture porosity observed. Growth of additional axial compression reduced all types of porosity. Fracture preparation of the sample with an initially small fracture porosity was predominantly accompanied by a decrease in total and intergranular porosity and increase in fracture porosity, i.e., growth of microcracks. At the same time, during fracture preparation of a sample with an initially large value fracture porosity, an increase in total and intergranular porosity and decrease in fracture porosity were observed, which is characteristic of dilatancy processes. Differences in the fracture nucleation of sandstone samples were revealed, which indicates that their initial fracture porosity has a significant effect on them.

A option of the methodology for observing PM_2.5 and PM₁₀ particle mass concentrations based on an Arduino UNO board and Sensirion SPS30 laser sensor has been developed. The measuring system built according to the technique was used in a field experiment, as well as in continuous observations at a stationary point: the Moscow Geophysical Monitoring Center of the Institute of Dynamics of Geospheres, Russian Academy of Sciences (IDG RAS). Examples of variations in the observed characteristics are given, which indicate the possibility of using the instrumental system in addition to already existing devices when observing the geophysical environment. Continuous monitoring of microparticle concentrations at the Geophysical Monitoring Center will make it possible not only to assess the degree of atmospheric pollution in the megalopolis, but also highlight certain trends, frequencies, and patterns. Such monitoring will also make it possible to reveal the contribution of various sources to the increase in microparticle concentrations, as well as the effect of pollution on different geophysical fields.

In the current article, we examine the tectonophysical parameters of Mt. Beshtau. A number of facts indicate that the Mt. Beshtau is developing according to the protrusive uplift type, as is the Khibiny Massif. Concentric fracturing was recorded along the periphery of the massif, which emphasizes the newest stage of development of the massif. The overwhelming number of determinations of slickensides indicate a normal-fault kinematics. Calculation of geological stress indicators allows us to suggest an extensional regime. These data lead to the conclusion that during the neotectonic stage, Mt. Beshtau is undergoing an annular subsidence with he general uplift of the massif. In the southwestern part of the faults, confined to the Skala vein system, strong seasonal radon emanation anomaly has been revealed, which is probable evidence of high-permeable rock of the massif. The results from studying this territory by different tectonophysical methods indicate the high reliability of the conclusions.