Seismic Instruments最新文献

The study compares seismic hazard assessments of the territory of Uzbekistan, obtained with the same input parameters, but using different methodological approaches: the Riznichenko approach based on the theory of macroseismic and spectral-time shaking and the classical Cornell probabilistic approach based on the full probability theorem. As seismic source models, linearly extended sources (seismogenic zones) and area sources (quasi-uniform seismological provinces) were considered. The authors used a number of their own damping dependences, established from analysis of isoseismic earthquake patterns in Central Asia, when assessing the seismic hazard of the study area in terms of macroseismic intensity, along with the Shebalin dependence, obtained from global data (I = 1.5M – 3.5 log R + 3). To estimate seismic hazard in engineering seismic indicators, the dependences built into the R-CRISIS software package, developed over the past 10–12 years for shallow active crust and stable regions, were used as the ground motion equation. For a 50-year seismic impact nonexceedance probability P = 0.90, the maximum differences in seismic hazard assessments using the two considered approaches for the entire seismically active part of the study area are ∆I = 0.39; for P = 0.95, ∆I = 0.54; for P = 0.98, ∆I = 0.61; and for P = 0.99, ∆I = 0.76. A similar comparison of seismic hazard assessments in the values of maximum ground motion accelerations leads to the following figures: for P = 0.90, ∆a_max = 75 cm/s²; for P = 0.95, ∆a_max = 111 cm/s²; for P = 0.98, ∆a_max = 167 cm/s²; for P = 0.99, ∆a_max = 273 cm/s².

The Yuzhno-Sakhalinsk Seismological Regional Information Processing Center (RIPC) recently used the Richter magnitude M_wa to estimate the energy level of Far Eastern earthquakes. To date, this is the most common energy characteristic in the operational catalog of the RIPC. The basis is digital waveforms of regional seismic stations emulated to the characteristics of the Wood–Anderson seismograph. In the present paper, the results of determining the magnitude M_wa in Russian Far Eastern conditions are analyzed. The magnitude determination accuracy is estimated, and station corrections are obtained. The regression relation M_wa and Japanese Meteorological Agency magnitude M_j showed a high similarity between these scales. This made it possible to use M_j as the reference when studying the features of M_wa. The regional seismic network makes it possible to correctly estimate the magnitude M_wa at a regional distance (up to about 1000 km), including for deep-focus earthquakes (up to 600 km). Transfer relations between M_wa and other mass-determined regional energy characteristics of earthquakes are obtained. The M_wa scale can be used to estimate the energy level of any earthquakes in the Kuril–Okhotsk and Sakhalin regions in the magnitude range of weak and moderately strong events and is recommended for inclusion in regional earthquake catalogs for the Russian Far East.

The paper discusses the applicability of the horizontal-to-vertical spectral ratio for ground motion (H/V method) to estimate the seismic intensity increment and trace the bedrock surface covered by soil layers. The first issue is the classic seismic microzoning problem; the second is related to structural mapping of the upper part of the geological profile. The authors assess the possibility of using a single station to estimate the intensity increment without synchronization of data at a given point at a site with records based on reference rocks. It is shown that such an approach is invalid, because the maximum variations in the H/V ratio during a day may reach 2.7 times; a degree of intensity of 0.8 will correspond to such variation. At the same time, it is shown that the resonance frequencies of soil layers are stable. If the mean velocities of seismic waves are known at some points of profile surface, the position of the underlying bedrock top can be traced with confidence.

In connection with the 50th anniversary of the destructive Dagestan earthquake on May 14, 1970, information on the parameters, manifestation features, and consequences of this seismic event was collected and summarized. The Dagestan earthquake became a very important event in the seismic history of the entire Caucasus. The reasons for this were determined by several of its features, the most important being that it was the strongest instrumentally recorded earthquake in the Caucasus at that time, and the nearest seismic station, Makhachkala, was at an epicentral distance of less than 30 km and recorded not only the main shock, but also a strong foreshock with its aftershock sequence. After the earthquake, a temporary seismic network was quickly deployed, which made it possible to trace in detail the development of the aftershock process of the main shock. Based on the literature data, the main parameters of the Dagestan earthquake and its most important consequences are discussed. The most realistic model of the source was constructed by S.S. Arefiev et al. (2004) based on data on the inversion of body waves from this earthquake. According to this model, Dagestan earthquake had a multiple source consisting of three subsources. The initial rupture (subsource), with a horizontal extent of 14 km, was located in the center of the focal zone at a depth of 9 km. The second rupture began about 2 s later, 10 km east of the first, at a depth of about 10 km and with a horizontal extent of 20 km. The third subsource was 10 km west of the first, at a depth of 12 km. The Dagestan earthquake made it possible to significantly refine the regional seismic hazard assessment. This was extremely important in regards to construction of the Chirkey hydroelectric power plant (HPP) with a high-altitude dam (232 m) in the 8-point shaking intensity zone for this seismic event. The creation of the reservoir itself during the construction of the high-pressure concrete dam of the HPP led to the impact of its filling and further seasonal fluctuations in the volume of the reservoir (about 3 billion m³) on the seismic activity in the upper part of the crust, with an area of at least 1000 km². This was the reason for the occurrence of induced technogenic earthquakes in this area. The effect of induced seismicity can be dangerous if completion of the dam and creation of the reservoir coincide in time with the natural rhythm of ordinary seismogenesis. It also turned out that powerful shaking of the upper part of the crust during the Dagestan earthquake disrupted the oil production regime in Dagestan.

The article considers the earthquake of April 5, 2017 with M_{W GCMT} = 6.0 near the Turkmen–Iranian border, northeast of the Iranian village of Sefid Sang. During the entire seismic history of the region, this was the strongest seismic event within a 45 km radius of the epicenter. The earthquake caused widespread destruction in four villages; two people died and 100 were injured. The shaking was felt in population centers in Iran, Turkmenistan, and other countries. According to the compiled isoseist map, the northwestern orientation of isolines of equal intensity, coinciding with the strike of the nearest faults, and strong damping of the shaking intensity across tectonic structures were established. The macroseismic field equation has been established, which is close to the Blake–Shebalin equation with average world coefficients. According to both equations, the shaking intensity at the epicenter is estimated as I₀ = 8. The northwestern (southeastern) orientation of the aftershock cluster and their southeast migration were revealed, which made it possible to choose the nodal plane of the focal mechanism with a similar strike as the active one. The fault plane parameters, length L = 30 km and width W = 12 km, have been estimated for the area of the highest aftershock density. The law of the decrease in the number of aftershocks with time has been established, which indicates rapid decay of the aftershock process.

The article studies the characteristics of seismic coda wave attenuation in the vicinity of the source of the 1902 Shamakhi earthquake and in adjacent zones of the Western Caspian region. The relationship between the features of seismic processes and spatial inhomogeneities of the attenuation field is considered. The attenuation field is represented by zones (blocks) with a high Q-factor and close to isometric in plan view, and by the linear zones of strong attenuation (weakened zones, which coincide with faults). Sources of the strongest earthquakes are confined to the zones of maximum attenuation contrast. It was revealed that the structure of the attenuation field agrees with the structure of the S-wave velocity field: low-velocity anomalies correspond to low-Q zones. Unidimensionally extended volumes of intense localized seismicity, located in weakened zones, are considered. In one of these volumes, in the focal zone of the 1902 Shamakhi earthquake, manifestations of active deep degassing processes were observed: mud volcano eruptions and earthquake swarms with upward-moving sources during a series have been recorded. It is noted that the most remarkable seismic events, and, above all, the major 1902 Shamakhi earthquake, correlate with the minima of the Earth’s rotation speed.

The article shows the relevance of integrating the main open hole logging methods for wells constructed during exploration and development of infiltration type uranium deposits. The article describes a new integrated downhole tool developed by the authors for simultaneous gamma, electrical, and directional logging. The downhole tool is based on a modular scheme; includes standard, modernized, and new functional logging units; and effectively combines analog, pulse, and digital output data formats. The modular architecture of the downhole tool allows open hole logging both individually, with separate methods and modules, and simultaneously in one common assembly. The results of field tests of the new tool at one of Russia’s infiltration deposits in the Trans-Ural uranium-ore district are presented, convincingly demonstrating the high accuracy of measurements and full compliance of the obtained logging data with regulatory instructions. Use of a new complex tool during geophysical surveys in the open holes of wells constructed during prospecting for, exploration, and development of uranium and ore deposits will increase the efficiency of logging operations, lower their cost, and reduce the forced downtime of drilling crews.

The modern seismological network of Karelia consists of four seismic stations. The number of network stations is small, and they are unevenly distributed over the territory of Karelia. Therefore, this seismological network is not efficient enough, and seismic events (earthquakes and quarry blasts) with different minimum magnitudes and different accuracies are recorded at different points in the territory. In order for events occurring at different points of Karelia to be recorded with the same accuracy and the same minimum magnitude, it is necessary to arrange the system’s seismic stations more evenly throughout the territory; i.e., the observing system must have the optimal configuration. Calculation of the minimum magnitudes of recorded seismic events for the optimal seismological network from 65 new and 4 currently functioning seismic stations shows that with an amplification in recording channels of 50 000, the network will reliably record earthquakes with a magnitude of 1.0 or more throughout Karelia. At the same time, the position of the seismic stations of such a network in Karelia is determined up to a parallel shift and arbitrary rotation of the entire observation system. Errors in determining the epicentral coordinates in latitude and longitude within the network will not exceed 0.5 km. The errors in determining the depths of earthquake sources recorded by the system throughout Karelia do not exceed 1.0 km at the center of the network and can reach 2.0 km only on its periphery.

The proposed article touches upon a number of issues related to the impact of natural or man-made vibrations on soil masses and geological processes. The impact of seismic waves on the soil mass is determined by both direct mechanical action and absorption and dispersion of seismic energy, which in turn is triggered by phenomena when elastic energy is transforms into thermal, electrical, and chemical energy. The design and construction of modern buildings requires consideration of the possible negative effects of vibration loads. The objective of this article is to draw the attention of prospectors, designers, and those who operate structures to the need to study the influence of man-made vibrations from various sources.

Active faults in Southern Transbaikalia, some of which are elements of the Mongolian–Okhotsk lineament, are still poorly studied seismically. The Chikoy fault has been characterized by weak earthquakes over a 100-year period of instrumental observations, which yields no knowledge of the seismic potential of the fault. However, distinct manifestation of a fault scarp in the modern relief suggests high rates of tectonic movements along it. This is also confirmed by the seismotectonic deformations discovered during our field studies. Field works in the Chikoy fault zone revealed signs of a seismogenic feature of the fault in segments with a total length of at least 32 km. Analysis of the morphology of the scarps and sections indicates that the dislocations were formed as a result of at least two to three paleoearthquakes with magnitudes of 7.0–7.2. According to absolute (radiocarbon) and relative (based on the slope of the scarps) dating data, the age of paleoearthquakes range from 5–8 ka, 2373–2832 years ago, and later than 760 years ago. The high seismic potential of the fault revealed by seismogeological data is confirmed by historical evidence of an earthquake with M = 6.0 that occurred here in 1830.