Seismic Instruments最新文献

This paper briefly reviews modern approaches and methods for generating digital elevation models. The focus is on photogrammetric model generation methods: photogrammetry itself relies on a series of overlapping photographic images. In our study, a camera was mounted on an unmanned aerial vehicle (UAV). We describe the major steps in generating digital elevation models, gear requirements, image capture details, and software used. Lastly, we show how we created a local digital elevation model of part of an island near the northern shore of Lake Ladoga.

This article continues a study of spatial rhythmic variations of various parameters using spectral-profile analysis. This procedure has been successfully used in the Atlas of Natural Processes. In this study, manifestation of spatial rhythmic variations is considered with the example of vertical profiles composed of P-wave velocity values for three superdeep boreholes: Kola (SD-3), Vorotilov (VDB), and Ural (SD-4). Using wavelet analysis, we estimated the periodicities in the velocity variations and represented the seismoacoustic models of the SD-3, VDB, and SD-4 geological sections as a set of blocks of varying size in the upper part of the Earth’s crust. These blocks reflect the influence of different geodynamic processes at various depths. It was found that the hierarchical sequence of the average vertical sizes of the blocks corresponds to the hierarchical model of the geophysical medium. The geodynamical processes, which resulted in cyclic variations in P-wave velocities in the geological sections of the Kola (SD-3), Vorotilov (VDB), and Ural (SD-4) superdeep boreholes include: alternating epochs of volcanic activity and sedimentation, tectonic movements, impact events, penetration of intrusive bodies and amphibolite dikes in the intervals of relatively weaker rocks, and metamorphic and metasomatic alteration of rocks. Study of the sections of the superdeep boreholes can be considered, to some extent, a real-scale simulation of the crustal structure of the Earth up to large depths. Studies have shown that variations in the physical properties of crustal rocks and the hierarchical sequence of the average vertical sizes of blocks have common properties of cyclic processes involved in the “self-organization” environment.

The history of instrumental observations in the northwestern East European Platform and the degree of seismological knowledge of the White Sea region is presented. The paper describes the modern seismicity of the White Sea region and considers in detail the strongest earthquake in the region for the last decades, which occurred on November 5, 2019, and, according to some features, can be thought to be unique to the region. The earthquake epicenter is located in the area of the interbasin bar dividing the Kandalaksha and Kolvitsky grabens. The calculated focal mechanism of the source shows the normal dip slip of blocks along the fault, which corresponds to he modern extension of the crust and the continuing development of the Kolvitsky graben.

The paper shows the possibilities of complex morphometric analysis of the relief and computer modeling of modern geodynamics to identify seismically active areas in two different regions well studied in seismotectonic terms: the Northwestern Caucasus and the Voronezh anteclise. At the quantitative level, the majority of earthquake epicenters are associated with areas of increased values of a number of morphometric characteristics of the relief (depth of vertical dissection, steepness of slopes, density of lineaments and elongation lines, etc.). Computer modeling has been used to identify areas of possible formation of new fractures, within which 80 and 65% of earthquake epicenters of the Northwestern Caucasus and Voronezh anteclise, respectively, are located. The shares of the area of these regions are 55% (for the Northwestern Caucasus) and 36% (for the Voronezh anteclise), which indicates the informative nature of the results obtained. The research is significant, because the methods and approaches used may be in demand when delineating inferred seismically active areas of territories where detailed seismological observations have not been carried out.

Repeated geodetic (ground and satellite) and gravimetric observations were carried out at the geodynamic test site at the Zhanazhol oil field (Kazakhstan) in 2010–2013. The results of leveling observations were analyzed, and local anomalies of Earth’s surface vertical displacements in fault zones were revealed. Comparison of the results of ground-based and satellite geodetic observations showed that the distribution of vertical displacements of the Earth’s surface obtained from GNSS measurements are in sharp contradiction with the releveling data. A paradoxical discrepancy between the ratio of vertical and horizontal displacements of the Earth’s surface throughout the entire field has been established. It is shown that in areas of maximum uplift or subsidence of the surface, intense horizontal displacements are observed, which contradicts the laws of geomechanics for deep objects with volumetric deformation. In these areas, horizontal displacements should have zero or minimum horizontal movement amplitude. The results of repeated leveling and gravimetric observations are compared. A regular relationship has been revealed between local subsidence of the Earth’s surface in fault zones and variations in the gravitational field. A correspondence has been established between the sign of displacements of the Earth’s surface (subsidence, uplift) and the features of development of the field. It is proposed to use geodynamic monitoring as a method for additional monitoring of field development processes.

The article proposes a methodological approach to comprehensively assess the impact of seismic hazard and vulnerability of construction objects and engineering infrastructure systems on the prospects for urban planning activities. The south of Eastern Siberia and territory of the city of Irkutsk are considered as examples. We have described the main factors determining the magnitude of seismic risk, as well as possible ways to reduce vulnerability in seismically hazardous areas. The importance of detailed information on seismic impacts on an urbanized territory in the past is emphasized for making balanced and well-grounded planning decisions. It is suggested that implementation of a comprehensive approach to urban planning activities can contribute to an acceptable seismic safety level of all objects under risk.

In 2012–2018, at the geodynamic survey area of the ultraviscous oil field of PJSC Tatneft, results of measurements of formations of the Earth’s surface were obtained using discrete geometric leveling and continuous satellite receivers (GNSS). Analysis of the results made it possible to compare the vertical displacement component obtained by two completely different measurement methods. The analytical model of the deformable formation made it possible to simulate subsidence of the Earth’s surface over the entire deposit, while showing consistency with the exceedance results obtained by the leveling method. The conducted spectral analysis according to GNSS data revealed a vast number of different spectra and also allowed us to calculate the trend velocity of the Earth’s surface.

The article presents a brief overview of the currently existing ideas about the seismotectonic situation in the Earth’s crust of Iran, which is experiencing intense compression in the northeastern direction as a result of collision of the Arabian and Eurasian lithospheric plates. The survey also involved geodetic data in the form of modern GPS measurements of horizontal surface displacements. The stress-strain state of the Earth’s crust of Iran (construction of the average focal mechanism) was assessed based on data on the total set of 945 focal mechanisms of earthquakes of average strength (4.4 ≤ M_W  ≤ 6.5) according to the ISC catalog, which occurred from 1975 to 2020, within 12 spatial samplings. The focal mechanisms of the strongest earthquakes in the last 50 years (M_W = 6.0–7.4) for one event in each of these samplings are also considered. The calculated parameters of the average mechanisms and focal mechanisms of strong earthquakes are compared both with each other and with the surrounding tectonic situation and the distribution of deformation velocity vectors according to GPS observations. A satisfactory correspondence has been established between all the comparable values. The differences in the type of formation of the seismogenic layer of the Earth’s crust of Iran in different regions are demonstrated. These differences are manifested in different ratios of shear and thrust components in the reconstructed mean mechanism in different spatial samplings. A similar difference is noted in individual focal mechanisms of the strongest earthquakes. However, it is possible to describe the observed nature of deformation of the crust of Iran within a single concept of collisional tectonics, caused by collision of the Arabian and Eurasian plates in the last 5 Ma.

On September 21, 2004, the series of perceptible earthquakes occurred near the city of Kaliningrad. This series of seismic events affected not only the Sambia Peninsula, but also the entire Baltic region up to southern Sweden and eastern Denmark. The following events were recorded instrumentally: the foreshock with a magnitude of 5.0, the main shock with a magnitude of 5.3, and several aftershocks. The above magnitude estimates correspond to the highest values provided by various agencies. The magnitude estimates are conservative, but in this case it is even more difficult to explain the abnormally high intensities in some locations. Abnormally high seismic effects can be explained in only two ways: either the influence of the geological medium structure, or the occurrence of new earthquakes, which were triggered by the fore- and mainshock. The first assumption is not supported by the results of seismic microzoning, because the maximum amplification of seismic intensity was only 0.6 at two sites. To explain the observed intensity, such amplification is too weak. We attempted to find factual material confirming the possibility of earthquakes triggered by the fore- and mainshock. The article analyzes the distribution of seismic effects from the September 21, 2004 Kaliningrad earthquakes within Kaliningrad oblast. The observed intensities are compared with the calculated seismic effects in terms of the seismic intensity scale. As a result, it was found that the observed level of seismic effects significantly exceeds the calculated one and cannot be explained by the effects from the fore- and mainshock because of ground conditions. The macroseismic surveys in the territory of Kaliningrad oblast revealed excessively large cracks in the ground with significant horizontal movements along them and an anomalous lowering of the water level in a pond near the village of Veselovka, despite the torrential rains the day before. According to the macroseismic data, the average value of the attenuation coefficient for the region under consideration was b ≈ 2.7, which is significantly lower than the world average. The acquired data gave us grounds to hypothesize about certain earthquakes that accounted for the anomalously high seismic effects in Kaliningrad oblast: these seismic events were triggered by the fore- and mainshock of the 2004 Kaliningrad earthquakes, but were not recorded by seismic stations. A conclusion is drawn about the stress state of the crust beneath the Sambia Peninsula. Therefore, trigger earthquakes are quite possible here.

The paper presents the results of long-term (55 years) ground-based geodetic observations with increased spatial and temporal detail (the distance between reference points is 0.3–0.5 km, and the intervals between measurements are 1–2 months) in the Ashgabat fault zone (Northern Kopet Dag); local (with a width of 0.5 km) anomalous deformations of the Earth’s surface with average annual deformations rates of 1–3 × 10^–5/year are detected. The results of comparing the velocities of vertical and horizontal displacements of the Earth’s surface in the Ashgabat fault zone with data on the modern kinematics of interaction of the Turan and Iranian plates, obtained from GNSS measurements according to the Iranian Geodetic Network, are discussed; it is shown that the rate of reduction of the Kopet Dag based on ground geodetic measurements is almost 100 times less than in GPS observations. This proves that local vertical displacement anomalies occur under conditions of a quasi-static regional stress field. Spectral analysis of long-term series of leveling observations was carried out, and the prevailing periods of anomalies of vertical displacements of the Earth’s surface were revealed. It is demonstrated that the annual harmonic dominates in the block parts of the leveling profiles. The maximum periods in the fault zone do not correspond to the annual component and have a shorter duration. It is established that the annual harmonic is associated with seasonal thermoelastic strain and local changes in the fault zone are caused by periodic changes in the pore pressure associated with the precipitation regime. A mechanism of parametric excitation of local vertical displacements of the Earth’s surface is proposed, when changes in the internal parameters of the medium (bulk elastic modulus) occur under stationary regional loading.