Studying locations of strong earthquakes (М≥8) in space and time in Central Asia has been among top prob-lems for many years and still remains challenging for international research teams. The authors propose a new ap-proach that requires changing the paradigm of earthquake focus – solid rock relations, while this paradigm is a basis for practically all known physical models of earthquake foci. This paper describes the first step towards developing a new concept of the seismic process, including generation of strong earthquakes, with reference to specific geodynamic features of the part of the study region wherein strong earthquakes were recorded in the past two centuries. Our analysis of the locations of М≥8 earthquakes shows that in the past two centuries such earthquakes took place in areas of the dynamic influence of large deep faults in the western regions of Central Asia. In the continental Asia, there is a clear submeridional structural boundary (95–105°E) between the western and eastern regions, and this is a factor controlling localization of strong seismic events in the western regions. Obviously, the Indostan plate’s pressure from the south is an energy source for such events. The strong earthquakes are located in a relatively small part of the territory of Central Asia (i.e. the western regions), which is significantly different from its neighbouring areas at the north, east and west, as evidenced by its specific geodynamic parameters. (1) The crust is twice as thick in the western regions than in the eastern regions. (2) In the western regions, the block structures re-sulting from the crust destruction, which are mainly represented by lense-shaped forms elongated in the submeridio-nal direction, tend to dominate. (3) Active faults bordering large block structures are characterized by significant slip velocities that reach maximum values in the central part of the Tibetan plateau. Further northward, slip velocities decrease gradually, yet do not disappear. (4) In the western regions of Central Asia, the recurrence time of strong earthquakes is about 25 years. It correlates with the regular activation of the seismic process in Asia which is mani-fested in almost the same time intervals; a recurrence time of a strong earthquake controlled by a specific active fault exceeds seems 100–250 years. (5) Mechanisms of all the strong earthquakes contain a slip component that is often accompanied by a compression component. The slip component corresponds to shearing along the faults revealed by geological methods, i.e. correlates with rock mass displacements in the near-fault medium. (6) GPS geodetic meas-urements show that shearing develops in the NW direction in the Tibet. Further northward, the direction changes to the sublatitudinal one. At the boundary of ~105°E, southward of 30°N, the slip vectors attain the SE direction. Further southward of 20°N, at the eastern edge of the Himalayan thrust, the slip vectors again attain the sublatitudinal direc-tion. High velocities/rates of recent crust movements are typical of the Tibet region. (7) The NW direction is typical of the opposite vectors related to the Pacific subduction zone. The resultant of the NE and NW vectors provides for the right-lateral displacement of the rocks in the submeridional border zone. (8) The geodynamic zones around the cen-tral zone (wherein the strong earthquakes are located) are significantly less geodynamically active and thus facilitate the accumulation of compression stresses in the central zone, providing for the transition of rocks to the quazi-plastic state and even flow. This is the principal feature distinguishing the region, wherein the strong earthquakes are loca-ted, from its neighboring areas. In Central Asia, the structural positions of recent strong earthquakes are determined with respect to the following factors: (1) the western regions separated in the studied territory; (2) the larger thickness of the crust in the western regions; (3) strong submeridional compression of the crust and upper lithosphere in combination with shear stresses; (4) high rates of recent crustal movements; and (5) the rheological characteristics of the crust.

The article presents a systematic review of the available tectonophysical data on the state of crustal uplifts and basins in intracontinental orogens. Based on results of the tectonophysical analysis of data on earthquake focal mechanisms for the Altai-Sayan and Northern Tien Shan regions, it is established that in many cases the crust in the basins and uplifts has antipodal structures, considering various types of the state of stresses. In the crust of the uplifts, maximum compression axes are usually sub-horizontal; in the crust of the basins, only the axis of the principal stress of minimum compression (i.e. maximum deviatoric extension) is sub-horizontal. These observations correlate well with estimations of deformations on the surface of the crust on the basis of the GPS-geodesy data, as well as with stress measurements taken directly on mining sites. The antipodal structures and physical fields in the crust of the uplifts and basins are not a random phenomenon. This suggests a common mechanism of deformation at the stage of active formation of the uplifts and basins. However, results of a similar tectonophysical analysis performed for the crust of the Pamir plateau and Tibet show that minimum compression stresses are subhorizontal in these regions, and the geodynamic type of the state of stresses is determined as horizontal extension or horizontal shearing. This pattern contrasts sharply with the type of the state of stresses of horizontal compression in the crust of the mountain ranges around the plateau (the Himalayas, Kunlun, Tsilian Shan, Hindu Kush), as well as with the state of stresses of active orogenic structures of the Tien Shan and Altai-Sayan regions.
Based on the stress values estimated for a range of geodynamic types of the state of stresses, it is estimated that additional compression stresses of the order of 5.4 kbar are required for the transition from horizontal extension to horizontal compression. If the regional strain rates currently recorded by the GPS-geodesy are taken into account, such additional stresses need to be applied for about 10 million years to fulfill the transition.

The article reviews three typical concepts concerning the age of the Baikal rift (BR) which development is still underway: 5 Ma (the BR development start in the Late Pliocene), 30 Ma (Miocene or Oligocene), and 60–70 Ma (the Late Cretaceous). Under the concept of the young BR age (Pliocene–Quaternary) [Artyushkov, 1993; Nikolaev et al., 1985; Buslov, 2012], according to E.V. Artyushkov, BR is not a rift, but a graben due to the fact that the pre‐Pliocene structure of BR does not contain any elements that would be indicative of tensile stresses. However, field studies reported in [Lamakin, 1968; Ufimtsev, 1993; Zonenshain et al., 1995; Mats, 1993, 2012; Mats et al., 2001] have revealed that extension structures, such as tilted blocks and listric faults, are abundant in the Baikal basin (BB), and thus do not support
E.V. Artyushkov’s argumentation. The opinion that BR is young is shared by M.M. Buslov [2012]; he refers to studies of  Central Asia and states that only the Pliocene‐Quaternary structure of BB is a rift, while the oldest Cenozoic structures (Upper Cretaceous – Miocene) are just fragments of the large Cenozoic Predbaikalsky submontane trough (PBT) which are not related to the rift. However, the coeval Cenozoic lithological compositions, thicknesses of sediment layers and types of tectonic structures in PBT and BB have nothing in common. Across the area separating PBT and BB, there are no sediments or structures to justify a concept that BR and PBT may be viewed as composing a single region with uniform structures and formations. The idea of the Pliocene‐Quaternary age of BR should be rejected as it contradicts with the latest geological and geophysical data. Seismic profiling in BB has revealed the syn‐rift sedimentary bed which thickness exceeds 7.5 km. Results of drilling through the 600‐metre sedimentary sequence of Lake Baikal suggest the age of 8.4 Ma [Horiuchi et al., 2004], but M.M. Buslov believes that it took only about 5 Ma to form the entire syn‐rift sequence of
Lake Baikal. In [Bazarov, 1986; Rasskazov et al., 2014; Mashchuk, Akulov, 2012; Hutchinson et al., 1993; Zonenshain et al., 1995; Kaz’min et al., 1995], the BR age is determined as the Miocene (Oligocene‐Miocene) according to the age of the Tankhoi
suite (Miocene or Oligocene‐Miocene) and the correlation between the lower seismostratigraphic complex (SSC‐1) and the Tankhoi suite [Hutchinson et al., 1993; Zonenshain et al., 1995]. The Tankhoi suite lies directly on the crystalline basement of the rift and is believed to mark the start of the Baikal syn‐rift profile. However, this concept does not take into account the main specific feature of the profile, i.e. a developing rift. As shown in Fig. 6, the most ancient elements in the syn‐rift profile are inside the deep part of the rift. At the day surface, the basement is overlaid by the younger elements of the sedimentary wedge due to the ‘expansion non‐conformity effect’ (as termed in [Khain, Mikhailov, 1985]). In our opinion, it is incorrect to correlate SSC‐1 and the Tankhoi suires – the representative seismic profile (Fig. 5) shows that SSC‐1 falls out of the profile before reaching the day surface and leans against the rising slope of the basement, while SSC‐2 correlates with the Tankhoi suite. Besides, correlating SSC‐1 with the Tankhoi suite is contradicting to the data of structural studies reported in [San’kov et al., 1997; Delvaux et al., 1997]. SSC‐1 originated before the time when the Lake Baikal region was impacted by the Indo‐Eurasian collision and formed under the influence of pure expansion when tensile stresses were oriented from NW to SE across the strike of the rift along the SE 145–150° azimuth [Zonenshain et al., 1995]. By the time of the SSC‐2 formation, the stress vector turned counterclockwise towards the NE‐SW direction at an acute angle to the rift strike. The Baikal rift structure was changed as the single‐sided basin was replaced by the SW‐NE stretching dual‐sided graben; it included SSC‐2 and was bordered by listric faults [Zonenshain et al., 1995]. Results of the structural studies conducted on the Lake Baikal shores [San’kov et al., 1997; Delvaux et al., 1997; Parfeevets, San’kov, 2006] suggest that during the Tankhoi period, the rift developed in conditions of transpression and transtension under the influence of stresses oriented subparallel to the strike of the rift and related to the Indo‐ Eurasian collision. This means that SSC‐2 (but not SSC‐1) correlates with the Tankhoi suite, and the age of the Tankhoi suite is not indicative of the BR age, and the concept of the Miocene (Oligocene‐Miocene) age of BR is thus discarded. The concept of the Late Cretaceous‐Paleogenic age of BR [Logachev, 1974, 2003; Mats, 1987, 1993, 2012; Mats et al., 2001; Mats, Perepelova, 2011] is most fully supported by the available geological and geophysical data. This age is evidenced by the Paleogenic (Eocene) palinspectra detected in core samples from deep wells drilled in the Selenga river delta, Southern Baikal basin [Faizulina, Kozlova, 1966]. Besides, the Paleocene‐Eocene pre‐Tankhoi sediments are discovered at the Khamar‐Daban shore of the Southern Baikal basin (the Polovinka river valley) [Mats, 2013]. The sediments of the BB weathering crust [Mats, 2013] correlate with the paleontologically dated Paleogenic sediments of PBT [Pavlov et al., 1976; Popova, 1981]. The BR ancient age is also confirmed by studies reported in [Nikolaev, 1989; Galazii et al., 1999; Kontorovich et al., 2007; Jolivet et al., 2009]. Our review of the BR age concepts gives grounds to conclude that the Pliocene‐Quaternary and Oligocene‐Miocene (“Tankhoi”) ages of BR should be discarded as not supported by the geological and geophysical data collected in the recent studies. Based on the comprehensive studies of the Baikal rift and taking into account an extension of the BR evolution by 60 to 70 Ma, we propose a new concept of the BR development and introduce a three‐stage model (Fig. 7) (as a replacement of the well‐known two‐stage model [Logachev, 2003]) and an impactogenic model as a supplement to the passive and active rifting models [Mats, 2012; Mats, Perepelova, 2011]. In our model, the first stage of the BR development is the Late Cretaceous‐Early Oligocene (70–30 Ma): in conditions of the general extension of the lithosphere, BR forms as a slot‐type (the term proposed by E.E. Milanovsky) rift and develops, as shown by the passive rifting model, at the background of the original peneplain until the time when the Baikal region is impacted by stresses resulting from the Indo‐Eurasian collision; the rift structure is a single‐sided basin that comprises the seismically transparent seismostratigraphic complex (SSC‐1); it is bordered at NW by the zone of listric faults. The second stage is the Late Oligocene‐Early Pliocene (30–5 Ma): BR develops under the impact of stresses resulting from the Indo‐Eurasian collision; the dual‐sided graben is formed; it comprises SSC‐2 that is stratified and deformed. The third stage is the Late Pliocene – Quarter (5 Ma till present): BR develops under the impact of stresses generated by local deep sources, as shown by the active rifting model [Logachev, Zorin, 1987; Zorin et al., 2003]; another single‐sided graben is formed; it is bordered by listric faults from the NW and comprises SSC‐3 that is stratified but not deformed.

Active faults of the Hangay-Hentiy tectonic saddle region in Central Mongolia are studied by space images interpretation, relief analysis, structural methods and tectonic stress reconstruction. The study results show that faults activation during the Late Cenozoic stage was selective, and a cluster pattern of active faults is typical for the study region. Morphological and genetic types and the kinematics of faults in the Hangay-Hentiy saddle region are related the direction of the ancient inherited structural heterogeneities. Latitudinal and WNW trending faults are left lateral strike-slips with reverse or thrust component (Dzhargalantgol and North Burd faults). NW trending faults are reverse faults or thrusts with left lateral horizontal component. NNW trending faults have right lateral horizontal component. The horizontal component of the displacements, as a rule, exceeds the vertical one. Brittle deformations in fault zones do not conform with the Pliocene and, for the most part, Pleistocene topography. With some caution it may be concluded that the last phase of revitalization of strike slip and reverse movements along the faults commenced in the Late Pleistocene. NE trending disjunctives are normal faults distributed mainly within the Hangay uplift. Their features are more early activation within the Late Cenozoic and the lack of relation to large linear structures of the previous tectonic stages. According to the stress tensor reconstructions of the last phase of deformation in zones of active faults of the Hangay-Hentiy saddle using data on tectonic fractures and fault displacements, it is revealed that conditions of compression and strike-slip with NNE direction of the axis of maximum compression were dominant. Stress tensors of extensional type with NNW direction of minimum compression are reconstructed for the Orkhon graben. It is concluded that the activation of faults in Central Mongolia in the Pleistocene-Holocene, as well as modern seismicity were controlled mainly by additional horizontal compression in the SW direction, which was associated with convergence of the Indian subcontinent and Eurasia. The influence of the asthenosphere flow in the SE direction at the base lithosphere is an additional factor facilitating strike-slip deformation of the crust in the study area and a possible explanation of divergent movements in the Baikal Rift, as well as the SE movement of the Amur plate. The Eastern Hangay crust is deformed under extension associated with a dynamic impact of the local mantle anomaly on the lithosphere. The boundary between the Amur plate and the Mongolian block (according to [Zonenshain, Savostin, 1979]) is fragmentary expressed in the tectonic structure. It represents a rim part of the deformation zone, embracing the Mongolian block and the adjacent uplifts of the Mongolian Altai, Tuva and Eastern Sayan. Along the boundary, compressive and transpressive strain occurred in the Pleistocene-Holocene.

Introduction. Determinations of (234U/238U) in groundwater samples are used for monitoring current deformations in active faults (parentheses denote activity ratio units). The cyclic equilibrium of activity ratio 234U/238U≈≈(234U/238U)≈γ≈1 corresponds to the atomic ratio ≈5.47×10–5. This parameter may vary due to higher contents of 234U nuclide in groundwater as a result of rock deformation. This effect discovered by P.I. Chalov and V.V. Cherdyntsev was described in [Cherdyntsev, 1969, 1973; Chalov, 1975; Chalov et al., 1990; Faure, 1989]. In 1970s and 1980s, only quite laborious methods were available for measuring uranium isotopic ratios. Today it is possible to determine concentrations and isotopic ration of uranium by express analytical techniques using inductively coupled plasma mass spectrometry (ICP‐MS) [Halicz et al., 2000; Shen et al., 2002; Cizdziel et al., 2005; Chebykin et al., 2007]. Sets of samples can
be efficiently analysed by ICP‐MS, and regularly collected uranium isotope values can be systematized at a new quality level for the purposes of earthquake prediction. In this study of (234U/238U) in groundwater at the Kultuk polygon, we selected stations of the highest sensitivity, which can ensure proper monitoring of the tectonic activity of the Obruchev and Main Sayan faults. These two faults that limit the Sharyzhalgai block of the crystalline basement of the Siberian craton in the south are conjugated in the territory of the Kultuk polygon (Fig 1). Forty sets of samples taken from 27 June 2012 to 28 January 2014 were analysed, and data on 170 samples are discussed in this paper.

Methods. Isotope compositions of uranium and strontium were determined by methods described in [Chebykin et al., 2007; Pin et al., 1992] with modifications. Analyses of uranium by ISP‐MS technique were performed using an Agilent 7500ce quadrapole mass spectrometer of the Ultramicroanalysis Collective Use Centre; analyses of strontium were done using a Finnigan MAT 262 mass spectrometer of the Baikal Analytical Centre for Collective Use. A natural uranium isotope standard (GSO 7521‐99, Ural Electrochemical Plant, Novouralsk, Russia) and a strontium isotope 
standard (NBS 987) were used for quality control of the measurements.

Results. The Kultuk polygon occupies large valleys of the Kultuchnaya, Angasolka, Talaya rivers and small valleys of the Medlyanka and Vorotny streams. The erosion basis of these valleys corresponds to the surface of Lake Baikal. In the valleys, there are several testing sites, including Staraya Angasolka, Slyudyanka, Vorotny, and Medlyanka. In the Kultuchnaya river valley, there are two sites, Tigunchikha and Verbny. Another two sites, Shkolny and Zemlyanichny, are located on slopes where no permanent water streams are available (Fig. 2). Measured U concentrations and
(234U/238U) in water from the sites of the Kultuk polygon are placed in Table 1.

Analysis and discussion of results. In water from an active fault, (234U/238U) depends on current deformation. The higher is the strain that causes fracturing, the higher is (234U/238U). The isotope composition of Sr sufficiently depends on the chemical weathering of rocks. The primary composition may be preserved in central parts of rock minerals and is detectable after preliminary treatment of an altered rock by HCl [Rasskazov et al., 2012]. In general, isotope
ratios of U and Sr in groundwater and surface water depend on the composition of host rocks, weathering, and alkalinity. Dissolved uranium migrates as uranyl‐ion (UO22+) characterised by its highest degree of oxidation (+6). Reduced forms of U(+4) are practically water‐insoluble. Therefore, an indirect assessment of oxidation‐reduction properties of the medium can be based on uranium concentrations. For the Kultuk polygon, surface water with low (234U/238U) is divided by uranium content into two groups, with anomalously low (below 0.009 mkg/l), and medium (~0.5 mkg/l) concentrations of uranium (components from the Medlyanka river and Kultuchnaya river, respectively). The U abundances reflect relatively reduced conditions in group 1 and more oxidized in group 2. The higher (234U/238U) in the surface water with intermediate concentrations of uranium (0.009–0.500 mkg/l) may indicate the admixture of a groundwater component (Fig. 3). Figure 4 shows relations between surface water and groundwater components in the Kultuk polygon in terms of U content. In Figure 5, the field of data points of U and Sr isotope ratios in groundwater from the Kultuk polygon is contoured by curved lines that meet with each other at compositions corresponding to the end members E (87Sr/86Sr=0.7205, 234U/238U=1.0) and NE (87Sr/86Sr=0.70534, 234U/238U=3.3). Uranium ratios of the former and the latter components show equilibrium and the most nonequilibrium compositions, respectively. The field is characteristic of water samples from the rocks of the southern suture zone of the Siberian craton. Shift of the data points of water from stations 26 and 1310 to the right of this data field (i.e. with relative increasing 87Sr/86Sr) is due to lateral transition from the rocks of the suture zone to the Archean rocks of the Sharyzhalgai block (Fig. 6). The isotope systematics of uranium and strontium in the strongly nonequilibrium uranium segment is supplemented by the systematics of uranium in (234U/238U) vs. 1/U diagram (Fig. 7). The U composition in water from station 40 reflects a combination of processes that take place at station 27 (i.e. in the central part of the deformation system) and at station 38 (i.e. at its periphery). Approximately equal contents of uranium at the three above‐mentioned stations may reflect similar oxidization levels of the medium. In the Southern Baikal basin, the Irkutsk Seismic Station recorded an earthquake of class 11.2 on 08 January 2013 [Map…, 2013]. The earthquake epicentre was located near Listvyanka settlement (51.85° N, 105°16 E), at a distance of ~100 km from Kultuk settlement eastward of the Obruchev fault. On 24 April 2013, an earthquake of class 10 took place near Kultuk settlement. Another seismic event occurred on 07 June 2013 (Fig. 8). During the monitoring period, nine maximums and ten minimums of (234U/238U) were recorded at station 9, i.e. nine full cycles can be identified (Table 2). At station 9, amplitudes of the cycles exceed the measurement error by a factor of 2 to 4. In Fig. 9, at the curve showing temporal variations of (234U/238U) in water from station 9, deviations from similar curves for stations 11 and 8 are not marked. Curves of temporal variations of (234U/238U) in water from stations 40 and 27 are shown in Figure 10. At the first station (diagram а), there were three time intervals of monitoring: (1) 12 April 2013 to 04 July 2013, (2) 04 July 2013 to 21 October 2013, and (3) 21 October 2013 to 17 January 2014. The initial and final intervals are similar and show an abrupt decline of the curve with a clearly manifested drop of (234U/238U) in the middle part, a minimum and subsequent rise of the curve. The time interval between the compared periods of observation lasted 5–6 months. This middle interval marked a rapid increase of the average values of (234U/238U) in the range from 2.34 to 2.47 activity units with the average rate of about 0.2 units per year. In the curve of station 27, there is also a downward segment with a drop, a minimum and subsequent rise of the curve, which is partly coincident in time with the initial segments for station 40. Correlation in time is revealed between the earthquakes that occurred in the Kultuk polygon and the drops in the curves for the above‐mentioned stations. Considering the shape of the final segment of the curve based on observations at station 40, it could be expected that the drop in the downward curve should have been associated with earthquakes. However, no earthquakes took place. In this regard, attention should be paid to the fact that a concurrent drop lacks in the curve for station 27. This suggests that an earthquake would happen only in a case of co‐seismic (234U/238U) drops at both stations. Seismic processes are controlled by triggers that provide the synchronization effect. Self‐organization processes may be the cause of its manifestation. Intervals of synchronization of oscillations (similar to foreshock activation) are indicators of the unstable state of a seismic region [Sobolev et al., 2005]. Similar information of the transition to the pre‐seismogenic state can be obtained by analysing variations of (234U/238U) in water from active faults. In the initial monitoring stage, the deformation system of the Kultuk polygon (stations 8, 9 and 11) developed slowly, 110–170 days per cycle. The first indicators of the pre‐seismogenic state in the polygon were observed as a coincidence of the minimums in the cycles of all the stations on 16 March 2013. The first seismic event took place on 24 April 2013, i.e. 39 days after all the maximums coincided. In the period of the pre‐seismogenic state, relatively short cycles were manifested. The second seismic event occurred on 07 June 2013. It was reflected by the coincidence of the minimums of short cycles at stations 8, 9 and 40 (Fig. 11). The entire monitoring period at the Kultuk polygon can be divided into two time intervals starting from (1) 10 July 2012, and (2) 07 August 2013. The first time interval includes the preparation and occurrence of seismic events of class 10 in the polygon. In the second time interval, the deformation system was further developed, and a new seismogenic state became possible. The time interval from 10 July 2013 to 07 August 2013 includes three stages starting from (1) 10 July 2012, (2) 10 January 2013, and (3) 12 April 2013 (Fig. 12). Higher strain values along the line from station 8 to station 9 were accompanied by the occurrence of deformation along the line from station 40 to station 47 (submeridional direction at 14°), which resulted in the synchronization of (234U/238U) at these stations (Fig. 13). At the background of the chaotic state of the monitoring system of the Kultuk polygon, it is possible to distinguish sequential self‐organization phases from а to г as evidenced by the azimuthal synchronization of the stations. The spatial development of the recorded processes was represented the sequential seismogenic activation of the western termination of the Obruchev fault (Fig. 14). From the analyses of temporal variations of U concentrations (Fig. 15), we infer that the dynamics of uranium ingress into water was different at stations 9 and 8. In the initial monitoring stage, the background extremely high values of (234U/238U) and concentrations of uranium were inconsistent at stations 9 and 8. Later on, at station 9, episodes of the high mobility of uranium from the deformation zone alternated with episodes of the high mobility of uranium from the oxidation zone. At station 8, in the period from 26 October 2012 to 04 July 2013, uranium impulses took place occasionally in the deformation zone, and a few were combined with earthquakes of class 9 or 10. From 07 August 2013, the above‐mentioned impulses were replaced by uranium impulses from the oxidation zone. At this stage, an anomalous ingress of uranium was recorded.

Conclusion. To validate the system of monitoring stations in the Kultuk polygon for earthquake prediction, spatial variations of (234U/238U) both in groundwater and surface water were studied. On sites of the tectonically stable areas, it was found that components of the surface runoff had admixtures of ground water components from the nearsurface water sources. On sites located at active faults, surface runoff components had admixtures of groundwater components from the deformation zone and oxidation zone. On sites located at active faults whereat permanent water streams lacked, the components from the deformation zone contained admixture of near‐surface ground water. The Sr–U‐isotopic systematics of groundwater at the Kultuk polygon was validated. Stations with high (234U/238U) (2.0–3.3activity units) and low 87Sr/86Sr (0.705341–0.712927) were selected for monitoring that lasted from 27 June 2012 to 28 January 2014. It was observed that (234U/238U) fluctuated in time, the duration of cycles and amplitudes of (234U/238U) fluctuations were variable, and the cycles of (234U/238U) in water were synchronized in the lines of the monitoring stations in the sublatitudinal and submeridional direction at the time intervals when seismic shocks occurred at the Kultuk polygon. The basic scenario of (234U/238U) variations in groundwater, recorded in the Kultuk polygon during the monitoring session, was examined in connection with the seismogenic activation of the western termination of the Obruchev fault. The SSE termination of the Main Sayan fault did not reveal any evidence on current tectonic deformations. The scenario of the reactivating Obruchev fault can be used for prediction of potential earthquakes in the Southern Baikal basin.