We carried out study crustal deformations in the Baikal-Mongolian area as a key Indo-Asian collision zone including kinematic, geodynamic, and active tectonic aspects. The GNSS measurement data over the last 29 years formed the basis for calculating vectors of horizontal tectonic movements at a qualitatively new level. Recent results show the southeastern movement of the Trans-Baikal sites at an average velocity of 2 mm yr- 1. We calculated the most realistic velocity of the opening of the Baikal Rift are of 0.9 +/- 0.1 mm year- 1. On the basic long-term measurements we are computed the parameters of the rotation pole of the Siberian block (phi.: 53.107 degrees; lambda.: - 99.793 degrees; Mg.: 0.249282 degrees Myr- 1). The maximum values of area extension rates are mainly confined to the central parts of the Baikal rift and the Tunka depression. The amplitudes of the relative deformation extension exceed 20 x 10-9 yr- 1. The strain rate analysis also provided an opportunity to distinguish three deformation domains - contraction-, extension- and transition-dominated. Narrow zones identified between the extension- and contraction-dominated deformation domains are confined to large seismic events therein. Transitional zones are found in the central Mongolia, Transbaikalia and Tuva, with dilatation rates ranging from -5 to 5 x 10-9 yr- 1. A sharp positive to negative dilatation transition boundary is associated with recent significant seismic events.

The origins and formation mechanisms of neotectonic structures in a part of the Mongolian-Siberian region were identified by geodynamic zoning based on multivariate statistical analysis of numerical data that describe geological-geophysical and geological-geomorphological processes. These processes in the regional lithosphere were described by a set of 11 geological and geophysical parameters, divided into three main groups using the hierarchical method of cluster analysis. The first group includes the seismic moment, the density of active faults, the recent horizontal strain rates, and the magnitude of the deep heat flow. The second group involves the thicknesses of the earth’s crust and exogenously active layer, the recent horizontal crustal velocities, and the amplitudes of vertical neotectonic movements. The third group includes gravity anomalies and the lithospheric thickness. The spatial grouping of the parameters by cluster analysis (K-means method) yields seven clusters, whose spatial position and composition are determined by the geological history, geological structure, geodynamic evolution of the region, and the recent strain rates. Some clusters characterize large rigid lithospheric blocks, while other clusters describe large active fault systems in the studied region. The search for latent factors that make the greatest contribution to the dispersion of the geological and geophysical parameter values was carried out using the principal component method, which allows minimizing the number of factors. Four main factors were identified for areas that differ in the morphology and origin of neotectonic structures: (i) higher horizontal compressive and tensile strains, (ii) dynamic effect of mantle anomalies, manifested in uplifts and doming, (iii) activation of thinned lithosphere within the boundaries of lithospheric plates or large blocks, and (iv) active shear deformation of the earth’s crust. The results of clustering and factor analysis of numerical data describing geological-geophysical and geological-geomorphological processes within the Mongolian-Siberian region are interpreted in the framework of physical mesomechanics.

The research provides an example of the GPS time series processing for monitoring of horizontal coseismic displacements during the 11 January 2021 M 6.7 Hovsgol earthquake, Mongolia. There has been developed a methodological approach to the study of coseismic displacements at the time of the earthquake. This paper presents the results of determining the values of horizontal coseismic displacements which are 0.6 mm in the junction zone between the Hovsgol and Tunka depressions and hundredths of a millimeter for the Siberian block and Transbaikalia areas. For stations located on the southern margin of the Siberian block and stations in Transbaikalia, the vectors of coseismic displacements are directed to the west. The calculated displacement vectors of the stations near the epicenter (MNDY and BADG) are directed to the southeast.

According to the data obtained on the equipment of the IEC SB RAS complex monitoring base for hazardous geological processes "Buguldeika" (Shared Research Facilities "Geodynamics and Geochronology" of IEC SB RAS) and Shared Research Facilities "Angara" of ISTP SB RAS an analysis of the characteristics of the Kudarinsky earthquake (09.12.2020) and the behaviour of the ionosphere during this event was carried out. The source parameters of the earthquake were obtained – the seismic moment of the earthquake (M0=3.02·1017 N·m), the moment magnitude (Mw=5.6), the source radius (2.43 km), and the stress drop (1.26 MPa).The analysis of the ionosphere behaviour carried out using GPS/GLONASS receivers did not reveal disturbances caused by the Kudarinsky earthquake, which is most likely due to the relatively small magnitude of this earthquake. An analysis of the observation series related to the Kudarinsky earthquake showed the efficiency of using the Core Facilities Centre equipment and complex monitoring bases for studying seismicity, which is the most dangerous natural process for the Baikal region.

The article deals with the first results of integrated geohazard monitoring conducted by the Institute of the Earth's Crust SB RAS on the territory of Pribaikalye in 2020. The pilot network consists of three sites: "Buguldeika", "Priolkhonye" and "Listvyanka", each of which is equipped with high-precision digital devices including a broadband seismic station, a GPS receiver, deformometers, a sensor of soil radon emanations, and an observation station for the Earth's electromagnetic environment. This equipment is designed to acquire quantitative information on rock deformation, recent movements and geophysical field variations for solving theoretical and applied problems of geodynamics and seismology, including development of earthquake prediction methods. In the vicinity of the sites, there have been made the hydroisotopic measurements as well as observations over the character of some of exogenous processes. Based on the comprehensive analysis of the seismological, tectonic, deformation and emanation data, acquired also through monitoring, there has been obtained the preliminary characteristics of the Kudarinsky earthquake (December 9, 2020, M W =5.6) that was followed by intensity 5 aftershocks in large cities of the southeastern East Siberia – Irkutsk, Shelekhov, Angarsk, Usolye-Sibirskoe and others. It has been found that the seismic event manifested itself almost in all the fields monitored. This implies the network efficiency for a purposeful study of the precursors of large earthquakes which can initiate the development of other hazardous geological processes in Pribaikalye. The deformation monitoring data show some general patterns of earthquake source evolution which corresponds to the fundamental principles of physical mesomechanics. This opens the prospects for diagnostics of the final phase of earthquake generation in the context of meta-instable state of deformation process and rock mass disintegration.

The measurement data obtained at the GPS network in the southwestern part of the Baikal Rift System for the period from 1994 to 2020 were analyzed. The spatial relationship between seismic events and tectonic strain rates was estimated. The field of modern horizontal motions and deformations was calculated for the Tunka, South Baikal, and Khubsugul depressions. The rotation pole of the Siberian block was defined. The general geodynamic setting on the western flank of the Baikal Rift System is characterized by low horizontal velocities in the range of 0.5–1.4 mm yr–1. Based on calculation of the relative deformations, the contrast zones of dilatation with narrow zones with the “non-Baikal” type of directions of deformation processes against the background tectonic extension regimes have been determined for the first time in the Bystraya and Khubsugul tectonic depression. Tectonic stresses are accumulated in these narrow zones and released in earthquakes.

First results of the analysis of GPS measurement data obtained from 18 sites of two local networks in the vicinity of Ulaanbaatar (Mongolia) for the period 2010-2015 have been presented. Horizontal velocity vectors are consistent with each other in the ITRF2014 system and with the velocities of the IGS permanent station ULAB. The sites move in the E-SE direction at a rate of 25-30 mm/yr, with the displacement azimuth averaging 105 degrees. With respect to Eurasia, the vectors for most of the sites are slighly turned to the south, but they are still of SE orientation with the azimuth range of 130 degrees-150 degrees and magnitude values of 2-4 mm/yr. Relative horizontal velocities tend to decrease towards southeast that determines a zonal distribution of different type of relative strain patterns. The western part of the Ulaanbaatar network is characterized by the W-E oriented extension with the elongation rate epsilon(1) = 12-16 x 10(-8) yr(-1). The shortening NW-SE trending strain with calculated value epsilon(2) = 22.4 x 10(-8) yr(-1) characterizes the network's eastern part. The highest values of the maximum shear strains (epsilon(max) = 10-14 x 10(-8) yr(-1)) form an extended area in the center of the testing ground, which is elongated in the northeastern direction, conformably with the strike of the major geologic structures. The strain distribution pattern of the Emeelt network located within the eponymous seismogenic structures is characterized by the crustal elongation (5 x 10(-6) yr(-1)) trending SE-NW and less pronounced shortening in the SW-SE directions. The axial part of the fault crossing the network in the NW direction exhibits maximum deformations. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The article describes the possibility of using the passive satellite measurements of the atmosphere to investigate the vertical patterns of pressure, temperature and relative humidity and simulate the altitude dependence of the refractive index of air. The seasonal parameters were determined for the exponential model showing the tropospheric refraction over observation points IRKM (Irkutsk), ULAZ (Ulan-Ude) and BADG (Badary). Post-processing of the input GPS data was conducted to ensure the highest positioning accuracy. In addition to high-precision geodesy, the global positioning method was used for determining the total tropospheric zenith delays (ZTD), which values are used to solve the problems of radio physics and meteorology. The angles of refraction and the true distances were estimated and compared in different seasons of the year. This study shows that the angles of refraction at the observation points located in the Baikal zone do not differ significantly in order of magnitude from the values estimated for other climatic zones.

The Global Positioning System (GPS) based on satellites and the networks of dual frequency receivers are actively used for geodetic and geophysical applications, as well as for studying the ionosphere and troposphere. The atmospheric water content is in the focus of research as a key parameter for determining of the accuracy of weather forecasting and hydrological monitoring. The precision of atmospheric water content calculations depends on the accuracy of determination of the delays of signals propagating from GPS satellites to ground-based GPS receivers when geodynamic measurements are conducted. This paper describes a technique that allows us to estimate the integrated water vapor (IWV) in the atmosphere from measurements of GPS satellite signal delays. We consider remote sensing of the lower atmosphere by GPS measurements to detect the water vapor content in the conventional vertical column to the top level of the troposphere (up to 12 km above the Earth's surface). In studies of the propagation of signals from GPS satellites to ground receivers, the atmospheric water vapor is taken into account as a ‘wet’ component (ZWD) of the zenith tropospheric delay (ZTD). ZTD is the sum of ZHD (hydrostatic or ‘dry’ delay) and ZWD (‘wet’ delay). ZWD values can be converted with a very high confidence in integrated water vapor (IWV) values for each installed GPS receiver.

We have compiled and analyzed earthquake focal solutions for the territory of Mongolia and its surroundings in order to reveal a spatial variability of stress orientation and stress regimes of the crust. According to the stress inversion results, the SHmax is turning from W-E in the eastern Mongolia to SW-NE in the Gobi Altay and the central Mongolia, and then to S-N in the western part of the region. Comparison with data derived from GPS measurements shows that directions of the strain axes revealed by the geodetic and seismological observations are generally consistent. A contradiction is found for the Bolnai zone where results of GPS estimation indicate the predominance of extension (in the SE-NW direction), whereas earthquake data for the longer period of seismic observations reveal compression. Compression in this zone is mainly due to the Tsetserleg-Bolnai earthquakes contribution; however, a part of the recent data on focal mechanisms fits an extensional stress field with the NNW orientated extension axis. These data are in accordance with some published works which suggest a transtensive field from some structural geology studies in the eastern part of the Bolnai zone.The paper is supplemented with a list of M≥4.5 earthquake fault plane solutions and unpublished focal mechanisms for some M≤4.5 earthquakes of the northern Mongolia and the southern Baikal region.

The Global Positioning System (GPS) based on satellites and the networks of dual frequency receivers are actively used for geodetic and geophysical applications, as well as for studying the ionosphere and troposphere. The atmospheric water content is in the focus of research as a key parameter for determining of the accuracy of weather forecasting and hydrological monitoring. The precision of atmospheric water content calculations depends on the accuracy of determination of the delays of signals propagating from GPS satellites to ground-based GPS receivers when geodynamic measurements are conducted. This paper describes a technique that allows us to estimate the integrated water vapor (IWV) in the atmosphere from measurements of GPS satellite signal delays.We consider remote sensing of the lower atmosphere by GPS measurements to detect the water vapor content in the conventional vertical column to the top level of the troposphere (up to 12 km above the Earth's surface). In studies of the propagation of signals from GPS satellites to ground receivers, the atmospheric water vapor is taken into account as a ‘wet’ component (ZWD) of the zenith tropospheric delay (ZTD). ZTD is the sum of ZHD (hydrostatic or ‘dry’ delay) and ZWD (‘wet’ delay). ZWD values can be converted with a very high confidence in integrated water vapor (IWV) values for each installed GPS receiver.

We have compiled and analyzed earthquake focal solutions for the territory of Mongolia and its surroundings in order to reveal a spatial variability of stress orientation and stress regimes of the crust. According to the stress inversion results, the SHmax is turning from W-E in the eastern Mongolia to SW-NE in the Gobi Altay and the central Mongolia, and then to S-N in the western part of the region. Comparison with data derived from GPS measurements shows that directions of the strain axes revealed by the geodetic and seismological observations are generally consistent. A contradiction is found for the Bolnai zone where results of GPS estimation indicate the predominance of extension (in the SE-NW direction), whereas earthquake data for the longer period of seismic observations reveal compression. Compression in this zone is mainly due to the Tsetserleg-Bolnai earthquakes contribution; however, a part of the recent data on focal mechanisms fits an extensional stress field with the NNW orientated extension axis. These data are in accordance with some published works which suggest a transtensive field from some structural geology studies in the eastern part of the Bolnai zone. The paper is supplemented with a list of M≥4.5 earthquake fault plane solutions and unpublished focal mechanisms for some M≤4.5 earthquakes of the northern Mongolia and the southern Baikal region.

A continuously operating GPS network, comprising seven permanent observation sites, is created to study the geodynamic processes in the Baikal region. Processing of the initial GPS data provides continuous atmospheric data in the form of total zenith tropospheric delay, which can be used for meteorological and climatological studies. The total delay is the sum of “dry”, or hydrostatic, and “wet” components. The wet component determines the total water vapor amount and amount of precipitable water over the measurement site. Thus, GPS measurements make it possible to obtain initial data for creating new numerical models of zenith tropospheric delay and total precipitable water vapor for meteorological applications.

The contemporary horizontal movements and deformations in the central and southern parts of the Baikal depression are analyzed, and their relationship with contemporary seismicity is studied. Based on the long-term measurements by the Baikal geodynamical GPS monitoring network, the refined estimate is obtained for the velocity of the divergence of the Siberian and Transbaikalian blocks, which is found to occur in the southeastward direction (130°) at 3.4 ± 0.7 mm per annum. This agrees with the parameters of the long-term extension component estimated from the geological data and with the direction of extension determined from the seismic data. The distribution of the displacement velocity across the strike of the rift, which gradually increases from one block to another, suggests a nonrigid behavior of the continental lithospheric plates at the divergent boundary. About 30% (1.0–1.5 mm per annum) of the total increase in the velocity is accommodated by the Baikal Basin. The strain rate within the trough reaches 3.1 × 10−8 yr−1 and decreases on either side across the structure. The character of distribution of the horizontal displacement velocities on the Baikal divergent boundary between the Eurasian and Amurian plates favors the model of passive rifting. The zones of highly contrasting topography and increased seismicity are localized within the area of contemporary deformations, and the seismic moment release rate directly depends on the strain rate. Here, the rate of the seismic moment release rate makes up a few percent of the geodetic moment accumulation rate calculated by the approach suggested by Anderson (1979). Based on the coherence between the graphs of the rates of geodetic moment accumulation and seismic moment release rate by the earthquakes with M ≥ 5.0 during the historical and instrumental observation periods, the contemporary seismic hazard for the South Baikal Basin could be assessed at a level of seismic event with M = 7.5–7.6.

Estimations of the zenith troposphere delay (ZTD) detected at primary GPS data processing using GAMIT program are received on the base of multiyear measurements of radio signals on a net of regular GPS stations of ULAZ, IRKT and BADG spaced out up to 230 km. ZTD reflects variations of different atmosphere processes. The detailed analysis of GPS data of the ULAZ station for the period of 1999-2011 is presented.

Based on multiyear measurements of present-day motions in the central area of the Baikal rift system, new data on the kinematics of horizontal motions, relative horizontal deformation rates, and rotation velocities in the area of junction of the South Baikal, North Baikal, and Barguzin rift basins have been obtained. This area is an intricate structure with two transfer zones: Ol'khon-Svyatoi Nos and Ust'-Barguzin. It is shown that crustal blocks are moving southeastward, normally to the structures of transfer zones and at an acute angle to the Baikal Rift strike, which corresponds to the right-lateral strike-slip extensional faulting along the major structure. The average horizontal velocities increase from 3.0 mm yr(-1) in the northern South Baikal basin to 6.5 mm yr(-1) in the Barguzin basin. The elongation axes prevailing in the study region are mainly of NW-SE direction. The areas of intense deformations are confined to structures with high seismic activity in the South Baikal and, partly, Barguzin basins. This confirms the existence of a present-day zone of the Earth's crust destruction in the Baikal rift system, which is the most likely source of strong earthquakes in the future. Two zones with rotations in opposite directions are recognized in the rotation velocity field. Clockwise rotation is typical of structures of N-NE strike (Maloe More basin, southern North Baikal basin, Barguzin Ridge rise). Counterclockwise rotation is determined for NE-striking structures (northern South Baikal basin, southern Barguzin basin). In general, the obtained data show an intricate pattern of present-day horizontal dislocations and deformations in the area of junction of NE- and N-NE-striking rift structures. This suggests left-and right-lateral strike-slip faults, respectively, within them. (C) 2013, V. S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B. V. All rights reserved.

Comprehensive analysis of the parameters characterizing contemporary and neotectonic deformations of the Earth’s crust and upper mantle developed in the Mongolia-Siberia area is presented. The orientation of the axes of horizontal deformation in the geodetic network from the data of GPS geodesy is accepted as an indicator of current deformations at the Earth’s surface. At the level of the middle crust, this is the orientation of the principal axes of the stress-tensors calculated from the mechanisms of earthquake sources. The orientation of the axes of stress-tensors reconstructed on the basis of structural data is accepted as an indicator of Late Cenozoic deformations in the upper crust. Data on seismic anisotropy of the upper mantle derived from published sources on the results of splitting of shear waves from remote earthquakes serve as indicators of deformation in the mantle. It is shown that the direction of extension (minimum compression) in the studied region coincides with the direction of anisotropy of the upper mantle, the median value of which is 310–320° NW. Seismic anisotropy is interpreted as the ordered orientation of olivine crystals induced by strong deformation owing to the flow of mantle matter. The observed mechanical coupling of the crust and upper mantle of the Mongolia-Siberia mobile area shows that the lithospheric mantle participated in the formation of neotectonic structural elements and makes it possible to ascertain the main processes determining the Late Cenozoic tectogenesis in this territory. One of the main mechanisms driving neotectonic and contemporary deformations in the eastern part of the Mongolia-Siberia area is the long-living and large-scale flow of the upper mantle matter from the northwest to the southeast, which induces both the movement of the northern part of the continent as a whole and the divergence of North Eurasia and the Amur Plate with the formation of the Baikal Rift System. In the western part of the region, deformation of the lithosphere is related to collisional compression, while in the central part, it is due to the dynamic interaction of these two large-scale processes.