Seismic Instruments最新文献

Aftershocks following a large earthquake are an inevitable part of the preparation and occurrence of large earthquakes. Depending on the location of the epicenter, tectonic–structural conditions of the epicentral zone, and earthquake intensity on the Earth’s surface, an aftershock cluster can cover different surface areas. Establishing the quantitative relationships between the aftershock zone and the main parameters of the earthquake (magnitude, rupture length, and slip value) can contribute to improving the model of an earthquake as a natural physical phenomenon. The extents of aftershock and deformation zones, as well as macroseismic changes on the Earth’s surface, indirectly indicate the intensity of the mainshock and the presence of portions with different degrees of weakening of rocks in the epicentral zone. This paper proposes a method to determine the area of such an aftershock zone using a deformational model of earthquake preparation and nucleation proposed earlier by the author. A new expression is obtained for determining the area of an aftershock zone depending on (i) the length of the rupture formed during the earthquake and (ii) the average slip along the rupture; expressions for the logarithmic and linear dependences of this area on the earthquake magnitude are also obtained. It is shown that the areas of the aftershock and deformation zones around an earthquake source are identical.

Earlier, it was shown that conventional algorithms for solving the inverse VES problem cannot achieve the accuracy required for precision monitoring of a geoelectric section, and regularized algorithms were proposed to improve the accuracy and stability of solving the inverse VES problem. In this paper, we test the resistivity contrast stabilization algorithm on synthetic data. For modeling, a geoelectric section is used, similar to the section of the Garm test site both in the set of layers and their resistivities, and in the characteristics of seasonal variations, as well as noise. It is shown that regularization of the inverse problem greatly reduces errors. The most significant effect is achieved by suppressing the buildup of resistivity. Estimates are obtained for the accuracy in solving the inverse problem, which can be achieved when working with experimental data.

The article presents the results of analyzing aftershock sequences initiated by underground nuclear tests conducted in North Korea in 2016 and 2017. Waveform cross-correlation and a multimaster method applied to phase association allowed us to find and analyze 91 aftershocks and group them into clusters associated with the underground explosions on September 9, 2016 (DPRK-5) and September 3, 2017 (DPRK-6). The duration, intensity, and sporadic nature of these two sequences indicate specific mechanisms of seismic energy release, which are probably related to the interaction of the destruction zones of DPRK-5 and DPRK-6 explosions and the collapse of their cavities with the gradual advance of the collapse columns to the free surface. The aftershock activity in 2021 suggested that the collapse process was not yet completed and predicted the occurrence of new aftershocks in the near future, which could end in the collapse column reaching the free surface. These assumptions were confirmed; during the preparation of this work, a strong aftershock with a magnitude of 3.85 was recorded on February 11, 2022, which, according to preliminary estimates, indicates the beginning of the final stage of the advance of the collapse column to the surface, the probability of which is discussed in this study.

The paper presents the results of the analytical and hardware development of a bipolar sensor for the concentration of small atmospheric ions, designed for long-term geophysical field observations. Theoretical estimates of the response function of the sensor are obtained. The dependence of the concentration of small atmospheric ions on the magnitude of the measured current of the aspiration capacitor and ion mobility spectrum is given. Numerical computations of the trajectories of small ions in an aspiration condenser of specified dimensions and geometry are performed. The probability of recording ions depending on their mobility is found. The circuit solutions and algorithms for the functioning of the hardware of the devices are described. Based on the development materials, prototypes of sensors are made. The technical characteristics and recommendations for the use of devices are given. Unlike analogues, the device is resistant to environmental influences. The sensors are tested in laboratory conditions and during the field observations of the electricity of the atmospheric boundary layer. In addition to being used as a part of a ground-based complex for geophysical observations, the developed sensor was used in an instrumental platform for balloon observations aloft. As a result of testing the devices, it was found that the functioning of the sensors is stable and the data are representative.

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.