Abstract: The study analyzes data from high-precision measurements of the apparent resistivity by a stationary multielectrode vertical electric sounding (VES) system including 12 current and 4 potential lines spaced 2–650 m apart. Observations had been being carried out at the Garm test area on a daily basis for 12 years in an earthquake prediction experiment. The use of special technical methods during measurements ensured an instrumental error of about 0.01%. The virtual error of each individual measurement of apparent resistivity (taking into account all possible noise) was 0.1–0.2%. The availability of more than 3000 VES curves measured in different seasons allows us to propose a new approach to constructing a geoelectric section model. To solve the inverse VES problem, a set of 36 averaged 10-day VES curves was analyzed, each of which was obtained by averaging approximately 100 individual VES curves accumulated in the same 10-day period of the annual (seasonal) cycle in different years. Comparative analysis of these curves made it possible to calculate and include corrections for stationary geological noise in the model. As a result, it was possible to substantially reduce (by an order of magnitude) the discrepancies in fitting the curves and dramatically narrow the equivalence domain. Based on the results of our analysis, we have constructed a model of a four-layer horizontally layered geoelectric section of the Khazor-Chashma depression to adequately describe not only the averaged section, but also its seasonal variations throughout the year. The stability in estimating the model parameters is studied. To further reduce the equivalence domain, we propose that the layer thicknesses be fixed. This model can be used not only to study the aforementioned characteristics of the section, but also to monitor time variations of resistivity in individual layers of the section. This will significantly improve the resolving power of systems for detecting time variations in geoelectric sections, including when searching for earthquake precursors.

Abstract: The main goal of this work is to provide real-time access to the data of the NSH tunnel tiltmeters via the Internet. Software is developed that solves this problem and also provides real-time visualization and archiving of data. The solution is based the specialized real-time protocol SeedLink, which ensures lossless data delivery with minimal transmission overhead. In order to simplify access to the device via IPv4 and to protect data from unauthorized access, a secure channel based on virtual private networks has been used. The solution was tested on two tiltmeters installed in the building of the Institute of Physics of the Earth, Russian Academy of Sciences (IPE RAS). Further device testing with an unstable power supply and communication conditions is planned. Therefore, the developed software was ported to energy-efficient ARM computers. Data transmission tests were carried out in the local IPE RAS network and in the wireless network of a mobile network operator. Real-time visualization of data from both tiltmeters and access to the archive are provided in addition to real-time access to data on the IPE RAS website.

Abstract: The implications of a broad range of factors for the intensity of the oceanic gravimetric effect has been estimated. These factors include dissipation, mass correction, the selection of the oceanic tidal model and Earth’s density model, and discarding the near-zone approximation, as well as allowance for the ellipticity of the Earth and the relative, Coriolis, and inertial accelerations. It has been shown that, with the presentday requirements to computational accuracy, the joint effect of these factors, rather than the separate contributions of each individual factor are of primary importance. The load Love numbers are calculated up to degree n = 50000.

Abstract: The paper reports on the development, creation of experimental models, and field tests of new-generation geohydroacoustic measurement buoys designed to be used both independently for taking acoustic, seismic, hydroacoustic, and seismoacoustic measurements at sea or on land (including boreholes) and in combination with distributed ice-class antenna systems to monitor Arctic water areas covered in drift ice. The geohydroacoustic ice buoy is a finished autonomous information-measuring device that envisages application as exchangeable receiver modules—new-generation combined vector–scalar hydroacoustic (0.01–2.5 kHz) and wideband molecular-electronic (0.03–50 Hz) receivers—and as an authoring tool for digitizing the received information, writing to internal memory, and subsequent timely transmission of the obtained scientific data. The design basis of the information-measuring system is a 24-bit analog-to-digital converter that can record signals in a wide dynamic range, which allows measurements with analog wideband sensors in both passive and active modes. A distinguishing feature of the geohydroacoustic buoy is its integrated power elements, which allows reliable autonomous operation of the entire measurement system for several weeks. The results of long-term lab-stand tests performed at the geophysical observatory of the Geological Service of the Russian Academy of Sciences (GS RAS) in Obninsk demonstrated the high-tech capabilities of the new-generation geohydroacoustic buoys. Comparative analysis when measuring signals caused by microseismic noise and teleseismic earthquakes confirmed that the proposed measuring device is not inferior to its foreign counterparts in its key indicators.

Abstract: In the fourth quarter of 2016, the system for monitoring induced seismicity in the Kuznetsk Basin (Kuzbass) began to record increasing seismic activity in the area of the Kaltan open-pit coal mine, which was struck by a series of seismic events felt in cities and settlements of the Kuzbass. In addition to the existing monitoring network, a temporary network of stations has been established, which has significantly increased the accuracy and representativeness of technogenic earthquake records. Markedly expressed seismic activation near open mine works (the Kaltan open-pit mine) has been revealed. The seismically activated area covers several open mine works and their vicinity. The strongest earthquakes have occurred outside the open-pit mine at the boundary of the dump. Inside the activated area, near the operating underground mine works (the Alarda mine), local seismic activation represented by low-energy technogenic earthquakes has been recorded. The largest number of perceptible earthquakes occurred in the fourth quarter of 2016. According to the monitoring data, the number of earthquakes with magnitudes 2.5–4 decreased in early 2017, but since February 2017, seismic activation has increased around the underground mine works, which was manifested as a significant increase in the number of low-energy technogenic earthquakes. In fact, the technogenic seismic hazard has shifted from open mine works towards the area of the operating underground mine.

Abstract: The first section of the paper describes the developed self-powered, chassis mounted mobile Energy-4 generator, which has a power of 29 kW and a maximum output voltage of up to 1200 V. The generator operates in the audio frequency range (2–2000 Hz) and is designed for electromagnetic sounding of the Earth’s upper crust in the search for minerals and monitoring of earthquake source zones in seismically active regions. The main power units of the generator are a PWM inverter and a step-up transformer. The inverter is powered by two DC generators mounted on the driveshaft of a truck, in the body of truck of which the generator is mounted. The circuit diagram and operation of the generator are considered, as well as individual design solutions that made it possible to increase the amplitude of the output voltage and, consequently, the current in grounded power lines. The second section is devoted to full-scale tests of the Energy-4 generator in the Kovdor-2015 experiment, during which multipath frequency soundings with 25 and 50 km spacings were carried out on the territory of the Enskii–Kovdor granite-gneiss complex composed of rocks of the Archaean basement of the Baltic Shield. As a result of the experiment, a ubiquitous intermediate conducting dilatancy-diffusion layer (DD layer) was found at depths from 2–3 to 5–9 km in an area of 100 × 200 km. The parameters of this layer have been investigated. The layer is considered a seismically active element of the brittle Earth’s upper crust with a thickness of 10–15 km.

Abstract: The paper considers the results of an archeoseismological approach to studying the seismic history of Crimea based on recent publications, devoted to reconstructing strong seismic events in the 15th–18th centuries. The reliability of the references involved is analyzed. Reconstruction of the timeline of earthquakes in Crimea is related to two problems: determination of doubtless evidence of a strong earthquake and dating of such an event. The first problem can be solved mostly by careful field studies using the developed technique and with representative historical, literary, and folkloric material, whereas dating of events encounters considerable difficulties. The main difficulties and limitations of this generally progressive research field are shown, which are related to both objective and subjective factors. Objective factors include, in particular, large uncertainty in establishing the chronology of seismic events using not only folkloric, but also historical data. The efficient cooperation of historians and seismologists is complicated by many unresolved issues in the reconstruction of historic events in Crimea, which deprives seismologists of a reliable basis and forces historians to rely on seismological conclusions that are not always valid. Subjective factors are related to lack of scrutiny when using sources and hasty conclusions. In addition, data on geological and man-made destruction in historical sources are used insufficiently. Despite doubts on the reliability of chronologically dating earthquakes, successful application of the archeoseismological method in Crimea is confirmed by solid evidence of strong seismicity. Obviously, to solve the dating reliability problem, further research and more complete reconstruction of Crimea’s history are needed.

Abstract: The characteristics of the shear wave attenuation field in the area of the Lop Nor nuclear test site, China, are considered. Methods are used that analyze the relative level of Sn and Pn waves (parameter Sn/Pn) and the slope of P-coda envelopes. An Sn wave is formed by shear waves reflected from multiple boundaries in the upper mantle, while P-coda is formed by S–P type conversion in the lithosphere of the source region. Twenty-six records of underground nuclear explosions (UNEs) and earthquakes obtained by station BRVK at epicentral distances of ∼1800–2000 km have been processed. It is found that from the late 1960s until the mid-1990s, the mean Sn/Pn values in the records of UNEs have substantially decreased and the slope of the P-coda envelope has increased in the area of the test site. These effects indicate an increase in S-wave attenuation in the lithosphere of the source region. A decrease in Sn/Pn with time in earthquake records for the test site region has also been observed after the termination of UNE series. Similar results were obtained earlier for the areas of the Semipalatinsk and Nevada nuclear test sites. The revealed effects are supposedly caused by deep fluid migration as a result of intensive long-term anthropogenic impact.

Abstract: Earthquakes that occur on the territory of Vietnam and especially in the South China Sea are a major hazard to the Vietnam population and infrastructure because of possible destruction and tsunamis, like those took place there in earlier times according to geological data. Therefore, in the early 2000s, the government of Vietnam decided to modernize and expand the network of seismological observations on the territory of the republic. First, it was planned to modernize the seismic network in Vietnam with 20 broadband seismic stations and then increase that number to 30. This raised the problem of the optimal arrangement of these stations in the country to predict earthquakes and study the structure of the crust and upper mantle of Vietnam. The map of Vietnam clearly shows the impossibility of constructing a single optimal observation network to locate earthquake hypocenters over the entire territory, because it is strongly elongated from north to south. Any seismological observation network for such an entire territory will not be optimal. In this case, we can speak about improving local observation networks for some areas, such as the north, center, and south of the country. This work estimates the efficiency (distribution of the minimum representative magnitudes and the error in determining the coordinates of earthquake hypocenters) for the new network of seismological observations in Vietnam, consisting of 30 stations. To improve the quality of the network in central and southern Vietnam, six more seismic stations are proposed. Such a network will allow more accurate determination of the hypocenter parameters in central and southern Vietnam. During the construction of the optimal network configuration, one of the main problems was the choice of an effective network radius. The formula for determining the optimal radius in the seismic observation network is obtained for the case of a uniform distribution of hypocenters in a certain cylindrical region based on the radius of the base and height of this cylinder. In this work, it follows from the formula that the radius of the optimal network should be no less than the radius of the hypocentral region. In our case, the choice of network radius is confined within the state borders and coastline of Vietnam. These restrictions are taken into account in the calculations to optimize the number of seismic stations and the configuration of their location in the country.

Abstract: The main distinctive features of ATLANTIDA3.1._2014, the first domestic program for the prediction of Earth tides, are discussed in comparison to similar programs of international authors, and some examples of the practical application of the program by different researchers are presented. The main functional features of the program are listed. Among them, the features for calculating amplitude delta factors of tidal waves for an oceanless Earth, as well as amplitude delta factors and phase shifts for an Earth with an ocean, tidal time series, and amplitudes and phases of the oceanic gravimetric effect, are especially distinguished. The theoretical developments included in the program are briefly described. The main differences of the latest version of the program are identified. The theoretical values of the amplitude delta factors for an inelastic self-gravitating rotating Earth, calculated with respect to the action of relative and Coriolis accelerations, as well as dissipation, are considered in detail. A total of 12 model variants are considered, which differ from each other by the inclusion or exclusion of separate factors affecting the result. The closeness of the results yielded by the program and the observations using the European superconducting gravimeters of the Global Geodynamic Project (GGP) is evaluated. It is shown that according to this criterion, our program surpasses the world’s most well-known counterparts. Tasks are listed that after their solution will expand the functional features of the program and clarify the results obtained so far.

Abstract: It is a common opinion that only crustal earthquakes can occur in the Crimea–Black Sea region. Since the existence of deep earthquakes in the Crimea–Black Sea region is extremely important for the construction of a geodynamic model for this region, an attempt is made to verify the validity of this widespread view. To do this, the coordinates of all earthquakes recorded by the stations of the Crimean seismological network are reinterpreted with an algorithm developed by one of the authors. The data published in the seismological catalogs and bulletins of the Crimea–Black Sea region for 1970–2012 are used for the analysis. To refine the coordinates of hypocenters of earthquakes in the Crimea–Black Sea region, in addition to the data from stations of the Crimean seismological network, information from seismic stations located around the Black Sea coast are used. In total, the data from 61 seismic stations were used to determine the hypocenter coordinates. The used earthquake catalogs for 1970–2012 contain information on ~2140 events with magnitudes from–1.5 to 5.5. The bulletins provide information on the arrival times of P- and S-waves at seismic stations for 1988 events recorded by three or more stations. The principal innovation of this study is the use of the original author’s hypocenter determination algorithm, which minimizes the functional of distances between the points (X, Y, H) and (x, y, h) corresponding to the theoretical and observed seismic wave travel times from the earthquake source to the recording stations. The determination of the coordinates of earthquake hypocenters is much more stable in this case than the usual minimization of the residual functional for the arrival time of an earthquake wave at a station (the difference between the theoretical and observed values). Since determination of the hypocenter coordinates can be influenced by the chosen velocity column beneath each station, special attention is focused on collecting information on velocity profiles. To evaluate the influence of the upper mantle on the results of calculating the velocity model, two different low-velocity and high-velocity models are used; the results are compared with each other. Both velocity models are set to a depth of 640 km, which is fundamentally important in determining hypocenters for deep earthquakes. Studies of the Crimea–Black Sea region have revealed more than 70 earthquakes with a source depth of more than 60 km. The adequacy of the obtained depth values is confirmed by the results of comparing the initial experimental data from the bulletins with the theoretical travel-time curves for earthquake sources with depths of 50 and 200 km. The sources of deep earthquakes found in the Crimea–Black Sea region significantly change our understanding of the structure and geotectonics of this region.

Abstract: The paper addresses the collection and analysis of new data on aftershocks that occurred within 20 days of the main shock of the December 7, 1988, Spitak earthquake, Mw = 6.8. The data were used to improve the location of aftershock hypocenters and magnitudes. Available data concerning this 20-day period were the least reliable in terms of completeness, representativeness, and the accuracy of hypocenter location and, in particular, estimation of energy classes and magnitudes. New data were retrieved from the records and bulletins of the seismic stations of the regional and global networks. Hypocenter parameters were determined by means of the minimization of wave travel-time residuals and subsequent double-difference hypocenter relocation. Digital records of the Obninsk and Arti seismic stations (Δ = 15°–18°) and five more distant stations (Δ = 34°–53°) were used to more accurately estimate the surface-wave magnitude of the main shock and strongest aftershock. The aftershock catalog of the Spitak earthquake was substantially revised. First, the previous hypocenter locations (Aref’ev et al., 1991) were improved using the double-difference method; second, new data were retrieved from the bulletins of Caucasian seismic stations. The minimum magnitude of completeness (M c = 1.9) of the new catalog for the first 20 days after the main shock (when there were no epicentral observations) is the same as that for the period from December 7, 1988, to December 31, 1989. The new catalog contains information on 2090 aftershocks with magnitude M = 1.9 and more for the period from December 7, 1988, to December 31, 1989. The double-difference method allowed the location of the epicenters of clustered earthquakes to be reliably estimated with a longitude error of no more than 4.6 km, a latitude error of 4 km, and a depth error of 5 km. The new spatial distribution of the aftershock hypocenters is better correlated with the tectonic setting than the old data. The new catalog can be used to assess seismic hazard after strong earthquakes in the region.

Abstract: Two groups of natural explosive processes in the permafrost zone are considered. The first group was described long ago and is associated with freezing of water under constrained environmental conditions (explosions of hydrolaccoliths and icing mounds). The second group has been identified in the last three years. It is associated with the release of underground gases formed during dissociation of gas hydrates contained in permafrost. In both cases, explosion is caused by overpressure in the soil mass containing free water or gas. Release occurs when pressure exceeds the strength of the top of the permafrost. A number of common features related to preparation of explosive processes in permafrost can be identified. The first is a local zone where an explosive substance is concentrated: a frozen streambed of a groundwater flow, a water concentration zone in the frozen soil mass, or gas hydrates in frozen soil. The second feature is pressure compressing the substance. The third feature is deformations in overlying rocks. If pressure increases slowly and the roof has time to deform, then plastic deformation takes place and frost mounds expressed in the topography are formed. If pressure increases quickly, plastic deformation may not occur. The fourth feature is the explosion itself. As many authors have described, explosion impacts on objects of various origin have common characteristics: ejection of gas-saturated water, gas, and ground and ice debris to a distance of up to tens and sometimes hundreds of meters. Dissociation of gas hydrates in frozen ground first produces microcracks, then, ascending at quite high pressure, gas hydrates form subvertical channels and elongated pores. Ascent of gas hydrates to the surface and gas evaporation are impeded by a durable monolithic overlying ice-soil “cover.” As a result of this, a crack–pore structure of the frozen ground forms under the cover. The width of the crack opening and pore size increase as pressure grows due to gas filtration from the source of gas hydrate dissociation. Cracks and pores merge to form a cavity, into which gas leaks. Once the ultimate strength limit is exceeded, the cover may not bear stresses and the accumulated gas potential energy in the cavity is released (i.e., it is transformed to kinetic energy) through an explosion. During development of the Arctic, the hazard of explosive processes for engineering structures will increase. Nevertheless, this group of hazards is not only not taken into account in designs and forecasts, they are not even treated as dangerous geological processes.

Abstract: The results of studies of the shear wave attenuation field in source zones of the 2003 Chuya, 1970 Ureg-Nur, 1991 Busingol, 2011 Sayan, and 2011–2012 Tuva earthquakes are presented. Attenuation fields in these source zones include blocks with a high Q-factor and linear weakened zones. The surface ruptures from the mainshocks of the 2003 Chuya and 2011–2012 Tuva earthquakes are located in the zones of strong attenuation. Epicenters of the mainshocks are located where the maximum contrast in attenuation is observed. In the source zones of large earthquakes in the Altai–Sayan region or near them, the zones similar to so-called seimogenic bodies described in the literature are found. These objects tend to linear zones with high attenuation and are characterized by an increased density of deepened earthquakes and also by deformations of near-vertical elongation. The obtained data suggest that the fluid factor could play certain role in the occurrence of large earthquakes in the Altai–Sayan region.

Abstract: The study of the stress-strain state of a medium in seismically quiet areas is difficult because of the absence of strong events. Under such circumstances, each earthquake, even relatively weak, is of high importance. In this case, all possible information on tectonic stresses and their dynamics, e.g., information on time, location, and magnitude of aftershocks, should be obtained from available seismic data. The earthquake near the town of Mariupol which occurred on August 7, 2016, had a body wave magnitude of 4.5–4.9 from the data of the different seismological centers. We detected 12 aftershocks that occurred within 5 days after the main shock using two seismic arrays (AKASG and BRTR) and one three-component station (KBZ) of the International Monitoring System, as well as two array stations of the Institute of Geosphere Dynamics, Russian Academy of Sciences. For six aftershocks, signals were found at three or more stations. The other aftershocks were detected from the data at two out of three nearest stations. Signal detection and association with aftershocks of the main shock, as well as estimation of magnitude and relative location of the found aftershocks, were carried out using the method of waveform cross-correlation (WFCC). The signals from the main shock that acted as the only master event (ME) for the WFCC method were used as waveform templates. To increase the signal-to-noise ratio and to determine the exact onset time of regular seismic waves from aftershocks, we used waveform templates of different length, from 10 to 180 s depending on the wave type and distance to the station, as well as band filtering in narrow frequency bands. The highest sensitivity of the detector and accuracy of the P-wave onset time estimates were reached when a waveform template included all regular waves from P to L g . Association of signals with aftershocks was based on back projection of signal arrival times to origin times using the travel time from a master event to the station, which was measured with a very low error, being equal to almost half of the digitization step length. To develop a seismic event hypothesis, the origin times at two or more stations should be spaced within a 2-s interval.

Abstract: An autonomous three-channel digital recorder developed at the Schmidt Institute of Physics of the Earth, of Russian Academy of Sciences is considered. The recorder was designed to meet the requirements of particularly difficult climatic conditions, minimum energy consumption, and ease of maintenance. Special attention is devoted to the reliability of data storage in case of sudden power loss, for which a new file-free recording format was developed. For each second of data recording, the system assigns a service line consisting of the exact time, the station code, and the station’s coordinates. This prevents loss of data when reading. When power is restored, the recorder automatically switches to the operating mode and continues the interrupted recording. The power supply for the analog part of the recorder is galvanically decoupled from the power supply of the digital part and carefully smoothed by special linear stabilizers and filters. To exclude the penetration of pulsations from the digital to the analog part by the common (grounded) wire, the control interface of the ADC is separated from the microcontroller by digital galvanic isolation circuits. Recorded data is recovered from the instrument by replacing the memory card, which takes just a few seconds. The control functions are also minimized, since the recorder has only two control buttons. The ease of maintenance allows quick installation of a large number of seismic stations with a small number of staff. The most important feature of the recorder is significantly reduced power consumption (less than 0.7 A h per day at a supply voltage of 12 V). This is five to six times lower than that of domestic and foreign counterparts and allows the recorder to operate on a single set of dry manganese–air batteries with a capacity of 150 A h and a weight of 4 kg for more than 6 months. As a component of seismic monitoring systems and in conducting epicentral measurements, these recorders are used in all climate zones of the Northern Hemisphere, from Serbia to Sakhalin and from Yakutia to Bangladesh; they have proved reliable and low-maintenance devices.

Abstract: At the beginning of the 21st century, a series of great earthquakes were recorded in northeastern Tibet, along the periphery of the Bayan Hara lithospheric block. An earthquake with MS = 8.1 occurred within the East Kunlun fault zone in the Kunlun Mountains, which caused an extended surface rupture with left-lateral strike slip. An earthquake with MS = 8 occurred in Wenchuan (China) on May 12, 2008, giving rise to an extended overthrust along the Lunmanshan fault zone. An earthquake with MS = 7.1 occurred in Yushu (China) on April 14, 2010; its epicenter was on the Grazze–Yushu–Funchuoshan fault; a left-lateral strikeslip offset was observed on the surface. An earthquake with MS = 7 occurred in the vicinity of Lushan on April 20, 2013; its epicenter was within the Lunmanshan fault zone, 103 km southwest of the zone of the catastrophic Wenchuan earthquake. An earthquake with MS = 8.2 occurred in Nepal on April 25, 2015. Based on the CSN seismic catalog, the energy of all earthquakes in eastern Tibet at the end of the 20th and beginning of the 21st centuries was estimated. It was found that Tibet was seismically quiet from 1980 to 2000. The beginning of the 21st century has been marked by seismic activation with earthquake sources migrating southward to surround the Bayan Hara lithospheric block from every quarter. Therefore, this block can be regarded as one of the most seismically active regions of China.

Abstract: The upper crustal location of the foci of the Spitak earthquake of December 7, 1988, and its aftershocks is proved. It is demonstrated that the seismological network in Armenia and Georgia allowed unequivocal focal depth identification based on the kinematic data. The waveforms of all the Spitak earthquakes are typical of sources in the upper crust. It is noted that up to now, mantle earthquakes in the Caucasus have only been revealed in the Terek–Sunzha depression.

Abstract: The paper presents the results of theoretical and experimental research into the structure of geohydroacoustic wave fields generated in continuous ice-covered northern seas. A simplified mathematical model is constructed that takes into account experimental data demonstrating that the generation of different types of geohydroacoustic waves in the lithosphere–hydrosphere–ice cover system are primarily influenced by the water layer with the ice cover. The seafloor structure mainly affects the characteristics of propagating waves rather than the generation of new modes. Mathematical modeling results have laid the basis for new technologies to localize inhomogeneities in ice-covered water areas. The main distinguishing feature of this novel technology for monitoring a medium under ice-covered marine conditions is the possibility to measure noise signal parameters without active geohydroacoustic emission sources. Methods that measure the characteristics of surface-type waves are the most promising for use in northern sea conditions, in particular, microseismic sounding and noise tomography. Integration of these methods combines the recent achievements of passive geophysics and takes into account the particularities of underwater acoustics. To obtain information on the wave propagation medium, both the wave field amplitude and phase characteristics are used. To detect particular types of waves in records, spatiotemporal signal processing methods are used with the appropriate choice of frequency range. The authors describe their new-generation seismohydroacoustic information-measuring modules (embedded buoys), which are equipped with vector and molecular-electronic primary transducers. The information-measuring modules are designed for combined use with distributed ice-class arrays capable of monitoring continuous ice-covered northern seas year round. Studies of how ice-embedded information-measuring systems function, as well as verification of the obtained theoretical results, were carried out during field tests in February 2017. At each measurement point, the receiver system consisted of three reference devices that took measurements on the seafloor, in the water column, and on the ice surface. Mockups of the tested geohydroacoustic buoys were embedded at points offset by 1 km. Dropped 32 kg weights were used as the sources. Controlled perturbations in the ice experiments made it possible to obtain qualitative spectrograms of geohydroacoustic perturbations in layered structures and analyze the dispersion curves. When the fundamental bottom modes were studied, the signal source consisted of an underwater charge at a depth of 10 m. The embedded seismohydroaoustic information-measuring modules successfully passed the ice-based tests in field conditions at low temperatures, demonstrating the reliability of the obtained seismohydroacoustic information. The experimental data agree very well with theoretical estimates obtained with the created model of a layered geological medium. These studies demonstrated that natural sea noise contains useful information reflecting the internal structure of the seafloor and the water layer and led to development of the instrumental and methodological foundations of a noise technology for localizing inhomogeneities in the aquatic environment and layered bottom structures of northern seas by means of passive microseismic noise monitoring.

Abstract: The data on the earthquakes of April 13 and 25, 1914 in Altai from (Novyi katalog…, 1977) have been summarized. Based on an analysis of the earlier publications and the new data from the initial sources, it has been shown that the only seismic event occurred on April 25 (12 old style), 1914. The weak differentiation of macroseismic effects over the area does not allow us to reliably locate the epicenter; the best spatial accuracy is ±50 km. Based on the entire data volume, the magnitude is estimated at 5.5 ± 0.3 which is slightly higher than was believed earlier.

Abstract: Earthquakes, which result from tectonic movements within the bowels of the Earth, reflect spatiotemporal changes in the stress field of the geologic medium. Weak regional earthquakes indicate the activation of some elements of seismotectonic zones and preparation of strong earthquakes. The travel times of Pand S-waves and V P /V S ratios are also a source of information on the regional tectonic setting; sometimes this information helps to reveal blind faults. The paper analyzes local earthquakes in a seismically active region, which comprises the Greater Caucasus, the Kura Depression, Transcaucasia, and the western Caspian Region. Based on a large database of hypocenter parameters, P- and S-wave travel times, and areal V P /V S ratio distributions, we identified seismotectonic zones with characteristic anomalous features and outlined gradient zones where V P /V S anomalies reverse sign. It is found that the V P /V S ratio field complies with the regional stress field and deep seismotectonic setting. Zones where anomalies reverse sign (gradient zones) are most likely confined to blind faults. Areas of the high gradient of the field can be put down to blind tectonic structures (faults) or the incipient sources of future strong earthquakes. V P /V S ratio monitoring and mapping will make it possible to identify the source zones of forthcoming earthquakes.

Abstract: The ultimate strain value for rocks in aggregate with their other physicomechanical characteristics plays a substantial role when solving different problems related to the bearing capacity and behavior of soils. These include determination of the maximum displacement, velocity, and acceleration values of soils during earthquakes and estimation of the potential strain energy accumulated in a medium during strong earthquake preparation. The latter parameter is also key in predicting earthquakes from the ultimate strain of rocks. The paper describes a technique developed by the author for determining the ultimate strain of soil columns under natural conditions from their relative slope on the surface after a strong earthquake. The empirical dependences of the ultimate strain of rocks on earthquake magnitude, relative slip, rupture length, and the seismic moment are obtained by analyzing their values calculated by the proposed method for 44 strong earthquakes with magnitudes of 5.6–8.5. A comparative analysis of the ultimate strain values obtained by other researchers by geodesic triangulation is performed.

Abstract: A network of stations for subsoil radon monitoring is in operation at the Petropavlovsk-Kamchatsky geodynamic testing area and is aimed at detection of strong earthquake precursors. At all stations, measurements are carried out using gas-discharge counters located at different depths within aeration zones of soft sediments. The volume activity of radon (VA Rn) is monitored at the most equipped station Paratunka (PRT) at three measurement sites located across the regional fault. The radon flux density (RFD) is measured from the surface. The article reviews responses in the dynamics of VA Rn and RFD from the surface at the PRT station prior to the Kamchatka earthquakes with magnitudes М W > 5 that occurred over the period of 2011–2016. The revealed RFD seasonal cycle is likely related to the seasonal variations in air temperature. The postseismic effect caused by the strongest deep Okhotsk earthquake (May 24, 2013, М W = 8.3) is detected in the RFD data. The behavior of VA Rn dynamics during time periods of the strong earthquakes is different. The results confirm the existing opinion on the formation of narrowly localized zones of Rn runoff to the atmosphere owing to both vertical and horizontal irregularities in the top layer of soil, which can react differently to changes in the geoenvironment stress–strain. On the basis of the real-time radon monitoring data, the authors have issued partially successful short-term prediction for several earthquakes. The results of this work confirm the opinion of many researchers that radon monitoring can be used in the short-term prediction of strong earthquakes.

Abstract: The possibility of creating a piezoelectric seismometer for recording angular accelerations during rotary motion of soil and structures is substantiated Two piezoelectric transducers with a common inertial mass are used in a single-component instrument The accelerometer is based on the principle of compensation of electrical signals with opposite polarities from linear motion with the addition of the signals proportional to the rotation of the same sensors The foundations of the theory and design elements of rotational piezoelectric accelerometers are considered The advantages of the instruments are emphasized when they are used in the near-field zones of strong earthquakes

Abstract: In order to estimate the influence of seismic effects from quarry blasts on the state of rock massif by means of electrotomography, magnetometry, and seismological observations, the variations in the physical properties of rocks before and after massive blasts have been studied. Experimental monitoring along the geophysical profile directed across one of the regional faults crossing the quarry field of the Neryungri open-pit coal mine has revealed no significant changes in the magnetic field after blasts. The revealed features include an increase in the electrical resistivity of rocks in the blast-directed wall of the tectonic fault and a decrease in the fault zone; the change in electrical resistivity in the hanging wall is insignificant. It has been found that the change in physical properties of the rock massif is determined mostly by the state (frozen or thawed) of the rocks, rather than by the power of the blast.

Abstract: Early warning systems are becoming increasingly important in the modern world. These systems combine several components: predictive systems (For example, tsunami warning systems), earthquake early warning systems, emergency message services, and systems of seismic damage monitoring. Information about shaking intensity becomes especially important in the case of a strong earthquake occurrence. These data are necessary for planning emergency rescue operations, but they are difficult to collect in a natural disasters situation because of possible communication problems. Application of data on instrumental seismic intensity may make it possible to solve this problem. Early warning systems predicting seismic intensity distributions just after the occurrence of an earthquake have already been developed in many seismically active regions of the world. Such a system also needs to be implemented in Kamchatka, where the strongest earthquakes can produce extremely high values of strong motion acceleration. As a result of the development of a system for seismological observation in Kamchatka, a unified specialized system for collection, transmission, archiving, and processing of seismic information was created. Seismological observations in Kamchatka were significantly improved with the update of the tsunami warning service in 2006–2011. As a result, a network of strong motion stations is currently operating in Kamchatka and can serve as a basis for creating a quasi-real-time seismic early warning system under the auspices the Kamchatka Branch of the Geophysical Survey, Russian Academy of Sciences (KB GS RAS). It uses data from strong motion stations to estimate the instrumental seismic intensity in quasi-real-time mode and visualizes the results. During the operational period while the service is being intensively used in the framework of the Seismic Early Warning Reports Tsunami Warning Service in the Kamchatka and Sakhalin branches of the GS RAS for real-time warning of interested parties about the shaking intensities at observation points, the technology implemented in this service has proved highly informative. In total, 75 messages on instrumental intensity in various places of Kamchatka krai and the northern Kuril Islands (Paramushir Islands) have been sent since the service was commissioned at the end of 2014. The currently operating version of the service has proved its informativeness and applicability for special departments of the Emergency Situations Ministry. In addition, real-time warning has improved coordination between the departments of KB GS RAS, and the results of this system are being used in a number of basic research projects. Further development of the service is related to the creation of denser instrumental networks to record strong ground motions and the transition to automatic decision-making and message sending.

Abstract: The Armenian seismic system, which has a threshold magnitude of 6.2, has been identified based on the method of seismic entropy, makes it possible to monitor nucleation of strong earthquakes in the magnitude range of 6.2 ≤ M < 6.6, as well as to assess the seismic situation in Armenia and neighboring countries. A study of energy and track diagrams has revealed a fan-shaped tectonic pattern of stress concentrations with an apex in the Kurdistan knot. The analysis of entropy accumulation in seismic cycles carried out for the hierarchy of seismic systems of the Armenian Highlands helped in the identification of prognostic criteria. The results have been compared to the dynamics of Akhurian reservoir filling in 1983–2016.

Abstract: The paper presents the results of application of satellite radar interferometry for solving a wide range of problems associated with deformations of the Earth’s surface. Displacements of the Earth’s surface at the Romashkinskoe oil deposit are estimated using the technique for reconstructing three components of the displacement vector developed at the Institute of Physics of the Earth, Russian Academy of Sciences; landslide activity above a section of the North Caucasus Railway tunnel near the village Mamaika (Bolshoi Sochi) is investigated, application of persistent scatterer techniques for estimating displacement fields in the territory of Moscow is tested, and coseismic and postseismic displacements in the area of the Altai Earthquake of September 27, 2003, are analyzed. The latest technologies make it possible to ensure that the obtained results correspond to the latest world standards and are competitive with the results obtained by foreign commercial companies for the territory of the Russian Federation and CIS countries.

Abstract: Software and some hardware aspects of a universal data acquisition system developed for geomagnetic and GNSS measurements are considered. The system’s design features, APIs, platform independence, and energy efficient hardware are described.