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 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.

We have studied the structural geology and geomorphology of the fault zones in the junction area of the Angara-Lena uplift and the Predbaikalsky trough. We have analyzed faults and folds and reconstructed paleostresses for this junction area named the Irkutsk amphitheatre. Our study shows that syn-fold (Middle Paleozoic) faults include thrusts, reverse faults and strike-slip faults with reverse components, that occurred due to compression from the neighbouring folded region. Recently, contrary to compression, faulting took place under the conditions of extension of the sedimentary cover: most of these recent faults have been classified as normal faults. In the Late Cenozoic, the platform cover was subjected to brittle and partly plicative deformation due to the NW–SE-trending extension that is most clearly observed in the adjacent Baikal rift. Thus, the divergent boundary between the Siberian block of the North Eurasian plate and the Transbaikalia block of the Amur plate is a zone of dynamic influence, which occupies the area considerably exceeding the mountainous region on the Siberian platform. Important factors of faulting are differentiated vertical movements of the blocks comprising the platform. Such vertical movements might have been related to displacements of brine volumes. In the Late Cenozoic basins, movements along separate faults took place in the Late Pleistocene – Holocene.

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.

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.

Today, one of the most topical questions in the recent geodynamics of eastern Asia is that concerning the existence of the Amurian Plate and its boundaries. An unambiguous answer is difficult to obtain because seismicity is relatively rare and weak and the plate boundaries are often geomorphologically unclear. One of the methods that can help is satellite geodesy. In the present study, the velocity field of recent horizontal crustal movements was obtained from five repeated GPS observations on the Amur–Zeya geodynamic test ground (Amur Region) in 2001–2007. On this basis, the parameters of the relative rotation of the Eurasian and Amurian plates were calculated. The coordinates of their rotation pole were found to be 122.285° E and 58.950° N, and the angular rotation velocity 0.095 deg/Myr. The resulting kinematic model describes the motion of the Eurasian and Amurian Plates as independent tectonic units. According to statistical analysis, this hypothesis is true at a confidence level of more than 99%. Also, calculations have shown that the eastern boundary of the Amurian Plate passes through a branch of the Tan-Lu fault system. The kinematic model for the Eurasian and Amurian Plates agrees well with data on the kinematics of active faults and the modern tectonic stress field at the plate boundary.