The article discusses a comparison of theoretical seismograms for two velocity models of the Earth's crust and P-wave arrival times estimated from experimental vibration seismograms for the 400-km long section of the Baikal–Ulaanbaatar profile. The theoretical seismograms were obtained by mathematical simulation of wave fields using the Earth's crust velocity models based on the data of the BEST and PASSCAL experiments. Vibration seismograms were obtained by measuring the wave field of a CVO-100 vibrator in the SB RAS Southern Baikal polygon. In the experiments, the vibration seismograms show that arrival times in the P-wave group correspond to the values for waves of large amplitudes in the theoretical seismograms. The P-wave arrival times in the theoretical seismograms of the BEST experiment are compared to the values in the experimental vibration seismograms for the 400-km long section of the Baikal–Ulaanbaatar profile. This comparison shows that the arrival times of maximum amplitude waves correspond to the theoretical hodographs of waves with velocities of 6.25–6.80 km/sec in the BEST experiment velocity model. At the same time, the experimental data set does not contain arrival times corresponding to longitudinal waves with Vp=7.25 km/sec, which are related to an assumed layer (more than 10 km thick) in the lower crust for the BEST experiment velocity model. In the experiments, the P-wave arrival times in the vibration seismograms correspond to the P-wave arrival times in the theoretical seismograms of the PASSCAL experiment throughout the entire 400-km long section of the Baikal–Ulaanbaatar profile. It is thus confirmed that the average values of the wave velocities in the PASSCAL velocity model have been reliably estimated. It should be noted that the experimental values of the arrival times of the first wave in the P-wave group are in agreement with the first arrival times in the hodographs of the theoretical seismograms for the velocity model in the PASSCAL experiment considering the distances from the source in a range of 65–380 km.

Establishing relationshipsbetween the regional seismicity andthe depth geometry and compositions of large-size density inhomogeneities of the upper crust is one of the ways to determine the parameters of mean long-term seismicity. Theoriginof geological bodies and mechanisms of penetration of intrusive bodiesinto the upper crust aredetectable from the shapes and sizes of such bodies.Knowledge on the shapes and sizes of large intrusive bodies is important for prospecting and exploration of mineral resources. Based on the medium-scale areal gravimetric survey data, a regional map of Bouguer gravity anomalies was constructed for theUlaanbaatar region, Central Mongolia.Interpreted gravimetric data from the solutions of the inverse problem of gravimetry based on the body-shape selection were used to developthe 3D models showing the largest crustal density inhomogeneities of the study area – the Tolskaya (Ulaanbaatar) basin, Nalaiha depression and Bogdoulin granite massif. It is confirmed that the basement of these depressionshas a block structure. The basement of the Tolskaya basinincludes two depressions, the western and eastern ones.In the western depression, the sediment thickness is 150 m. It amounts to 400 m in the eastern depression at the intersection of the Selbin and Tolskaya deep fault systems. The information on the shapes and thicknesses of the sediment bodiesisused in the seismic studies aimed at obtaining a more precise assessment of seismic hazard of the Ulaanbaatar city and the region. In the Nalaiha depression, the sediments are 800 m thick.The morphology of the basement and the thickness of sediments in this depression can be used to update the mining prospects of the Nalaiha coal deposit. The maximum thickness of granitoids in the Bogdoulin massif is 9.0 km. The area of its projection to the ground surface is twice as big as the area of the outcrops. Our research results can be useful for assessing the metallogenic specialization of granitoids, which indicators in relation to some minerals are related to the specific features of the Bogdoulinsky massif. Such indicators have beendiscovered by the geological, geophysical and geochemical methods. Our study shows that the geophysical methods (in particular, gravimetry) can considerably expand the knowledge of the morphology of geological objects at depth and facilitate reaching a new level in structural analysis, which is critical for developingnew ideas to clarify the geological history and tectonic conditions of the formation of the Mongolia-Siberian region.

Radiowave propagation techniqueshave been very rarely applied to investigate tectonic fault zones and geoelectric profilesof the Baikal rift zone. In our study, we used a combination ofground-penetrating radar (GPR) and radioimpedance techniquesin order to identify and investigatetectonic crustal fault zones in the study area. Using soundings in the super-long, long and ultra short radio wave ranges(from tens of KHz to few GHz), we detected the tectonic fault zones in the seismically active Baikal rift zone, specifically in the Tunka depression and the areas of Southern Baikal and Kotokel lakes.Faults and fault zones were identified from impedance variations and changes in the geoelectric profiles by analyzing the radio impedance profiles and soundings in the super-long and long radio wave ranges. The georadiolocation of fault structures in the ultra-short wave range made it possible to differentiate thepatterns of tectonic disturbances up to individual seismic dislocations in sedimentary and crystalline rocks and to determine the kinematics of movements in the fault zones. The techniques used in this study complement each other and ensure obtaining adequate quantitative descriptions of the study objects. By integrating varioustechniques of radio wave diagnostics, it is possible to obtain more detailed information on the structures of the tectonic fault zones. The results obtained in this study and the radioimpedance and GPR sounding and profiling techniques developed to investigate a heterogeneous underlying medium can be used in seismological and geological engineeringsurveys of the eastern and northern regions of Russia.

The water vapor content is calculated in a conditional vertical column to the tropopause level from remote sensing data on the lower atmosphere. The calculations are based on GPS measurements, surface meteorological data and vertical meteorological profiles produced by radiosondes.Atotal zenith tropospheric delay (ZTD) is estimated as a difference between an estimated straight line, along which the GPS signal propagates in vacuum, and alength of the pathbetween the signal source and the receiver, which is refracted in the real medium. A direct correlation is noted between changes in the ‘wet’ component of the tropospheric delay of the GPS signal and variations in the moisture content of the troposphere. A‘wet’ component value of the tropospheric delay can be converted with a very high confidence into a value of integral water vapor above the observation point.In order to determine the integral water vapor amounts over the ULAB (Ulaanbaatar) permanent GPS monitoring station, empirical equations were used for the linear regressions of the ratios of surface temperature and mean weighted temperature for the water vapor elasticity using the data of radiosondes launched in the city of Ulaanbaatar and Murensettlement. We studied the features of the dynamics of variations in the integral water vapor, surface values of atmospheric pressure, air temperature and precipitation volumes over the ULAB station, using the data of July 2016.

Seven gamma-ray bursts – GRB 130907A, GRB 140311B, GRB 140129B, GRB 160227A, GRB 120404A, GRB 110801A, and GRB 120811C were observed by the MSU MASTER (Mobile Astronomical System of TElescope Robots) Global Network. Full automation of the observations provided for obtaining unique data on the properties of early optical radiation accompanying gamma-ray bursts. The data are compared in the optical (MASTER), X-ray (SWIFT X-ray Telescope, XRT) and gamma (SWIFT Burst Alert Telescope, BAT) ranges. Based on the data obtained, two groups are identified, and their radiation mechanisms are revealed. The effect of gamma-ray bursts on the biosphere of the Earth is determined, and the estimates and the scale of such an effect are considered.

The ionospheric vertical sounding is a basic technique for studying the Earth’s ionosphere. Taking into account the fact that conditions for propagation of radio waves depend on the operating frequency, diagnostics of the ionosphere is performed using digital ionosondes that measure the delays of decameter radio signals of different frequencies. An ionogram is a display of the data produced by an ionosonde. It is a graph of the virtual reflection height of the ionosphere (actually, time between transmission and reception of a radio signal) versus sounding frequency.Vertical and near-vertical ionograms provide the major share of information about the space-temporal structure of the ionospheric plasma above the ionosonde. Of particular interest is investigating dynamic processes from the series of ionograms taken once each minute. Studying seismic ionospheric effects by minute ionograms can be highly informative. It is known that the parameters of the ionospheric layers can significantly vary both before and after an earthquake, and such deviations are detectable from ionosonde data. Recent observations show that the effects from an earthquake can occur at large distances from the epicenter.For instance, soundings in the Irkutsk region detected the anomalies that occurred several dozens of minutes after the main shock of the 11.03.2011 earthquake in Japan. At the initial phase, the anomaly was recordedas a multicusp structure in the ionogram, which was probably related tothe multiple layers of the ionosphere. This structure was interpreted by iterative reconstruction of the electron density profile in a one-dimensional approximation (stratified ionosphere), and the interperation was published. At the next phase, the ionograms showed a U-shaped structure with a specificmultiple reflection. Multipath propagation is usually associated with additional off-vertical ray paths, which are caused by traveling ionospheric disturbances (TIDs). In this regard, it is appropriate to use a 2D model of electron density, depending on both the vertical and horizontal coordinates.In our study, geometric optics approximation was used to simulatevertical ionograms under the conditions of strong horizontal gradients of electron density. The study results show that different positions of the U-shaped structure with respect to the main trace of the ionogram can be obtained for a single TID. Specific ray paths forming the additional traces of the ionogram are described.Depending on the TID location, the U-shaped structure can occur with or without a specificmultipath reflection.

Based on the output data of the magnetogram inversion technique, we analyze the dynamics of the Pedersen ionospheric currents and field-aligned currents (FACs) in the night mesoscale cells of the three main large-scale Iijima and Potemra Regions (R1, R2 and R0) during the expansion phase of the summer and winter substorms. FACs play a key role in the ionosphere-magnetosphere interaction. The continuity equation for the electric current density contains two types of possible feedback within the electric circuit parts that connect Pedersen currents and FACs in each cell. Pedersen ionospheric conductivity is dominant to Type 1, and the electric field dominates in Type 2 feedback. This paper studies both types of physical feedback in mesoscale cells of downward and upward FACs on the night side of the polar ionosphere from the data of two selected substorms of the summer and winter seasons in the northern hemisphere.

Within substorm activations during two superstorms (2000 and 2003) from the observations at mid-latitude geomagnetic observatories, we study short-period irregular geomagnetic pulsations and airglow in the 557.7 nm and 630.0 nm atomic oxygen emission lines, and in the 391.4 nm ionized nitrogen molecular band. Through the genuine magnetogram inversion technique, from the 1-minute data of the ground-based magnetometer global network, we investigate the distribution dynamics for field-aligned currents (FACs) in the ionosphere. The relation is shown between pulsation bursts and airglow disturbances in the post-midnight sector to precipitations of energetic electrons (~keV) and increase in the R2 upward FACs.

A superbolide with an estimated mass of 13,000 tonnes exploded at an altitude of 22 km over the city of Chelyabinsk (Russia) at 03 hours 20 min. 33 sec. UTC on February 15, 2013. It is now known as the Chelyabinsk meteorite. Over the past 100 years after the fall of the Tunguska meteorite on June 30, 1908, this event was an entry of the second largest object from outer space into the Earth’s atmosphere. In the literature describing the occurrence of magnetic effects during the fall and explosion of the Tunguska meteorite in the magnetosphere and atmosphere of the Earth on June 30, 1908, some researchers mentioned a change in variations in the Earth's magnetic field 80 minutes before the explosion itself. Similar features of the magnetic field components observed by the Irkutsk Magnetic Observatory are identified by the comparative analysis of the magnetic field variations during the falls of the Tunguska and Chelyabinsk space bodies through the magnetosphere.

In the studied region, vast land areas are influenced by construction and operation of large linear facilities, such as oil-gas pipelines, power lines, motor roads and railways. In the areas along and inside the construction right-of-way zones, considerable changes occur in landscapes, microclimate conditions, hydrological features of water bo­dies, and geological engineering characteristics of the rocks. Furthermore, anthropogenic soil materials are produced. In our study, such materials are termed ‘man-made / technogenic soils’, which means the soil material displaced during stripping operations in the areas allocated for construction of linear objects, and the soil material resulting from coal mining and quarrying. The above-mentioned changes in the geological environment lead to intensive exogenous geodynamic processes (EGP) taking place during construction and in the first years of the object operation. In areas where such objects are located near and in residential areas, the EGP impact is observed in the zones that have been previously not at all influenced or only slightly affected by EGP. In our comprehensive study aimed at the assessment of the scale of the regional landslide and mudflow processes, the physical and chemical properties of technogenic soils were determined, their mineral and chemical composition was analyzed, and the levels of chemical contamination of the studied soils were estimated. The research results can be used in engineering-geological, construction, hydrometeorological surveys, as well as forecasting the development of EGP and their impact on the territory adjacent to the large linear objects.

The study aimed at investigating the reaction of aresidential building (Series 111 nine-story block section) to seismic impacts that can lead to destruction of the building. The article presents the results of the retrospective analysis of the seismic resistance of nine-story block sections in the city of Gyumri (Leninakan) under the influence of the 07.12.1988 Spitak earthquake. The seismic resistance of the block section was calculated using the ‘pushover analysis’ method. Direct dynamic calculations were performed using a model of complex elastoplastic deformation of a mechanical system with two degrees of freedom. An external impact was represented by the earthquake records taken at the Ghukasyan station. Macroseismic survey data collected after the 1988 earthquake are presented. The block sections of Series 111 multistory residential buildings were designedbythe Armenian research and design institutions ArmNIISA and Armgosproekt in 1975 for construction in the Armenian Republic on sites with seismicity of 7–8 points. Vibration tests were conducted to test the strength of anine-storey block section in Yerevan in 1976, and it was discovered that the actual seismic resistance of the building did not comply with the current earthquake-resistant construction standards. However, the test results were ignored. On December 7, 1988, the earthquake took place, and the Series 111 buildings collapsed in the cities of Gyumri (Leninakan) and Vanadzor (Kirovokan). In the State Commission Report regarding the Series 111 design, it was concluded that considering the damage due to the violations of the design and construction standards and taking into account the inspection calculations, the accepted design solutions of the residential buildings did not meet the requirements of the regulatory documents for buildings designed to sustain seismicity of 8 points. Such design should not be used for seismic areas and must be critically revised. The retrospective analysis performed by the authors of this article on the basis of experimental data not only confirmed the conclusions of the State Commission, but also made it possible to establish a mechanism for the transition of Series 111 block-sections to the limit state. Unfortunately, the state management of the construction industry failed to use this information and did not take any urgent preventive actions.In fact, the authoritiesof the USSR supported the position of the Gosstroy of Armenia and allowed them to continue the construction of Series 111 residential buildings with minor changes. It was impossible to prevent the Spitak earthquake, but proper preventive actions could have reduced the amount of social and economic damage incurred due to the earthquake. The consequences of obvious design and construction errors discovered 12 years before the Spitak earthquake were ‘written off’and explained by the natural disaster, including underestimated standard seismicity, features of the engineering-geological settings, and the unfavorable spectrum of theactual impact. Thousands of people lost their life, and huge material damage was caused due to the loss of Series 111 residential buildings (300000square meters). Such was the price of professional incompetence and departmental ambitions.

In the study of the relationship between electromagnetic and seismotectonic processes, we analyzed the data of three observatories located at large distances, considering both latitudes and longitudes, and detected electromagnetic impulses in the frequency range from 0 to 5 Hz, which were recorded minutes before earthquakes. Detailed morphological and statistical analysis was carried out, and common and specific features were considered. Se­veral cases are discussed to illustrate the occurrence of electromagnetic precursor signals before the recorded devastating earthquakes in Japan, China, Romania and other seismically active regions. A qualitative explanation is given for the study results.

The M_L 6.1earthquake that occurred on June 18, 2013 in Kuzbass is the strongest seismic event related to mining operations in this region. Opinions about its genesis differ. On the one hand, its hypocenter and most aftershocks occurred directly underneath the Bachat open-pit mine, which suggests that this seismic event was due to anthropogenic impacts. On the other hand, the earthquake focus was located at a depth of several kilometers, which, according to some authors, argues against the anthropogenic factor– the technogenic change in the parameters of the stress field was insignificant againstthe lithostatic pressure and, especially, the rock strength (e.g. [Lovchikov, 2016]).Our study aims to discover and assess an impact ofthe mining operations in the near-surface areas of the crust, investigate whether the Bachat earthquake was caused by the mining operations, and clarify which processes in particularwere the most probable triggers of dynamic movement in the Bachat earthquake source. The probable geometrical parameters of the fault plane were estimated from the structural and tectonic conditions of the study area and the published locations of the aftershocks [Emanov et al., 2017]. It is established that seimic events of magnitudes similar to that of the Bachat earthquake cannot be caused by the overall anthropogenic load on the area, and it is unlikely that such a strong earthquake may occur due to the direct effects of seismic vibrations resulting from mass explosions during the mining operations. Our analytical models and numerical simulations, as well as the analysis of seismological observation data show that the most probable factor that initiated dynamic movements in the earthquake source wasthe extraction of the huge rock volume and its transportation from theBachat open-pit mine. It should be noted that the size of the zone, wherein the geomechanical initiation criteria are met, is considerably larger than the critical size of a nucleation zone for a M 6 earthquake. However, open-pit mining operations can hardly affect the localization of strong earthquakesources. Mining operations can only trigger a seismic event that has been already prepared by the natural evolution of the crust.

Inthe southern areas of the Siberian platform, geological and mining conditions are highly complex for design, drilling and construction of deep wells for oil and gas. Complicating factors are related to specific features of deforming cavity-fractured carbonate reservoirs. Geological models of carbonate reservoirsshould be designedon a case-by-case basis, taking into consideration the conditions of each specific field, including its complex filtration field, confirmed deformation of filteringfractures with constant parameters of the cavern component, etc. If an incomprehensive geological model is used for production planning with a lack ofa well-based approach to the development of a carbonate reservoir, design well flow rates may not be achieved, the field reserve coverage will be reduced and, consequently, the oil recovery ratio will be lower. When developing oil, gas and brine deposits, it is required to consider the natural-technical system of‘reservoir – reservoir’ (mechanical impact) – ‘reservoir fluid system and well’ (hydrodynamic impact) on the basis of a comprehensive analysis of its interrelated and interdependent components. Our study shows that each part of the system contributes directly to the entire complex. The stress state of the rock mass in the fluid-permeable part of the natural fractured reservoir and fluid-saturated reservoirs is dynamically changeable during the fluctuations of the pressure field of the reservoir hydrocarbon system at the initial penetration of a well into the reservoir. The authors analyzed the natural-technical system ‘well – fluid-saturated bed’ as a real on-line model of leaking – hydraulic fracturing based on a standard pressure vs. time curve during hydraulic fracturing. Based on the knowledge of the on-going processes in carbonate cavern-fractured reservoirs, it becomes possible to predict the reaction of the rock mass during hydraulic repression (i.e., during the initial penetration of a well into the reservoir) and depression (during testing and operations of a production well). All pressure effects hydraulically applied to the reservoir fluid system can lead to changes in the stress state of the natural reservoir. Thestress state with significantly changing permeability parameters of filtering fractures is among the most complex states of stress [Belonin et al., 2005; Borevsky, 1986]. It is important to take into accountthat such stress state transition during the drilling process is uncontrollable and unpredictable, which means that the reservoir permeability and porosity may be irreversibly affected and considerably reducedand, consequently,the oil well productivity and the final profitability of developing the hydrocarbon field will be significantly decreased. Based on the actual deep drilling data, we continue comprehensive studies of deforming fractured reservoirs in the area of the stress state of the rock mass and investigation of pressure characteristics of fluid systems and their mutual influence during hydraulic operations in the well completion cycle. Wehave analyzed the stress state of the rock mass in various reservoirs. Indicators characterizing a particular state of the rock mass are substantiated. Geological and technological recommendations are specified for the initial penetration of wells into the reservoir, as well as for testing the wells with respect to the state of the natural-technical system ‘well – fluid-saturated formation’. New geological and technological solutions are proposed.

Late Paleozoic and Early Mesozoic alkaline A-type granitoids (anhydrous, alkaline, moderately aluminous, ferruginous) are widely distributed in the structures of the Central Asian Fold Belt. In Northern Mongolia and Transbaikalia, there are hundreds of massifs that formed from the end of the Permian to the Middle Jurassic inclusive. These massifs are composed of alkaline granites, alkaline and alkali-feldspar syenites, and located within crustal blocks (terranes) of different ages and origins. New geochemical data obtained for the Kruchininsky, Sherbakhtinsky, Shabartay and Khamney massifs, as well as earlier published materials (Bryansk and Kharitonovo plutons), demonstrate that despite the general petrogeochemical similarity of the main rock types composing these plutons, their isotopic composition (Nd) differs significantly. Our studies suggest that the isotopic composition of Transbaikalia A-type granitoids is caused, on the one hand, by the crust permeability for mantle magmas and, on the other hand, by the material heterogeneity of the crustal magma sources themselves, varying from the Early Precambrian crystalline blocks to ‘young’ island-arc terranes.

The U-Pb and Lu-Hf isotope studies have been performed to investigate detrital zircons from metaterrigenous deposits (Nel, Kurnal and Amkan formations) of the Un’ya-Bom terrane of the eastern part of the Mongol-Okhotsk fold belt. The concordant ages of the youngest zircon in the metasiltstone of the studiedformations are as follows: 213±3.6 Ma –Nel, 194±4.4 Ma –Kurnal, and 202±2.5 Ma – Amkan. The new data suggest that a previouslyassumed(Middle Jurassic) age of the Amkan formation is uncertain. Most likely, the Kurnal and Amkan formations are of the same (Early Jurassic) age. In any case, a relationship between these formations needs to be clarified. In combination with the data from previous studies of the Tukuringra terrane, our study results show that the Early Mesozoic sedimentary rocks in the structure of the eastern part of the Mongol-Okhotsk fold belt are more abundant than it is currently assumed. Our study results suggest that during the accumulation of the Nel, Kurnal and Amkan formations, the materials were supplied from different provinces, especially from the Amur superterrane (i.e. from the south, in modern coordinates), as well as from the frame of the North Asian craton (i.e from the north, in modern coordinates), although the contribution of the craton source was insignificant.

Based on the statistical data of the Global Volcanism Program of the Smithsonian Institution and published materials, we present a comparative analysis of caldera-forming eruptions on global scale. The geodynamic settings and genesis of the caldera-forming eruptions with basaltic-andesitic magma compositions are described. The origin of the majority of mafic ignimbrites was related with external water. Such ignimbrites were generated in a submarine environment or with a contact with water. The newly obtained data, paleogeodynamic reconstruction and geological mapping of Miocene mafic ignimbrites of the Eastern volcanic belt (EVB) of Kamchatka confirm their genesis in costal-marine environment. These new data show significance of paleoreconstructions in studies of paleo-volcanoes and relief-forming pyroclastic rocks.