This paper discusses the results of a study of a rare natural phenomenon—the Utaat-Minchuur hot vapor anomaly located in the east of Mongolia. The first information about it appeared several centuries ago, but until now this phenomenon has not received due attention, and the question of its origin remains controversial. According to the authors, two main hypotheses are most likely. The first involves an underground coal fire. This is supported by the widespread occurrence of vapor-bearing coal deposits in the area and the constant formation of fresh depressions of ground. The second hypothesis suggests the presence of an endogenous heat source. This can be confirmed by the presence in the released gas of significant amounts of ammonia and carbon dioxide, which are characteristic of volcanic processes. In addition, effusive rocks are widespread in the vicinity of the vapor anomaly. At a distance of 8 km from the vapor anomaly, the ratio of 3 He/ 4 He isotopes in water samples from a self-flowing well was 1 × 10 –6 , which exceeds the similar ratio in many thermal springs of Mongolia. Based on the results of drilling operations, the presence of clays with a high content of organic matter, which were heated to a temperature of more than 60°C, was revealed in the upper part of the rock formation section. To clarify the conditions for the formation of a single heat source, it is planned to conduct geophysical research and drill deep exploration wells. Thanks to the combination of balneological factors (high vapor temperature and the presence of ammonia and a number of microelements), Utaat-Minchuur is a very promising object for the development of sanatorium and resort construction. Here, patients with diseases of the musculoskeletal system, peripheral nervous system, kidneys, etc., will be able to receive treatment. The experience of balneological use of natural vapor is known in a number of resorts around the world, such as Yangantau (Russia, Republic of Bashkortostan), Obygarm (Tajikistan), and Lorderello (Italy).

Active faults in Southern Transbaikalia, some of which are elements of the Mongolian–Okhotsk lineament, are still poorly studied seismically. The Chikoy fault has been characterized by weak earthquakes over a 100-year period of instrumental observations, which yields no knowledge of the seismic potential of the fault. However, distinct manifestation of a fault scarp in the modern relief suggests high rates of tectonic movements along it. This is also confirmed by the seismotectonic deformations discovered during our field studies. Field works in the Chikoy fault zone revealed signs of a seismogenic feature of the fault in segments with a total length of at least 32 km. Analysis of the morphology of the scarps and sections indicates that the dislocations were formed as a result of at least two to three paleoearthquakes with magnitudes of 7.0–7.2. According to absolute (radiocarbon) and relative (based on the slope of the scarps) dating data, the age of paleoearthquakes range from 5–8 ka, 2373–2832 years ago, and later than 760 years ago. The high seismic potential of the fault revealed by seismogeological data is confirmed by historical evidence of an earthquake with M = 6.0 that occurred here in 1830.

The article analyzes possible mechanisms behind the formation of Proval Bay, Lake Baikal, as a result of the Tsagan earthquake (12 January, 1862, М = 7.5 ± 0.3) and estimates the recurrence rate of destructive earthquakes in the Selenga River delta based on investigations of seismic deformations in mine workings. Earlier unpublished results of seismogeological and geophysical studies are presented. Geological and geophysical studies of seismic dislocations in the epicentral zone of the Tsagan earthquake indicate that the source of this earthquake could have been associated only with the major Morskoy fault. The displacement along this fault, as well as the one along the zone of the branching Del’tovyi (Delta) fault, contributed to the occurrence of a tsunami and to the landslide mechanism behind the formation of Proval Bay. Paleoseismological interpretation of the trench sections and the results of radiocarbon dating show that seismic events similar to the Tsagan earthquake also occurred in 1399–1496 CE, 1256–1401 CE, 887–1150 CE, and 233 BCE–221 CE in the north of the Selenga River delta. This gives an average recurrence rate of destructive earthquakes in the region as once every 500 years. Trenching and geophysical studies have established the features of oblique-thrust slip kinematics in Holocene, Pleistocene, and Neogene–Quaternary sediments along the Delta fault. It is possible that a geodynamic compression regime took place over relatively short-term intervals. Our conclusions do not contradict the geological and geomorphological conditions in the region or the historical information about the dislocations and surface effects of the Tsagan earthquake.

Abstract —In order to determine the seismotectonic activity of faults in the Holocene, we performed trench studies of the ruptures produced by the catastrophic Mogod earthquake (5 January 1967, M = 7.5–7.8, I0 = 9–10) in the junction zone of the N–S striking Hulzhin Gol fault and the NW striking Tullet fault. Paleoseismic interpretation of seismic-deformation sections and radiocarbon dating of the samples allowed determining the kinematics and obtaining, for the first time, the absolute ages of paleoevents preceding the Mogod earthquake. Analysis of the tectonic conditions for realization of earthquake sources has shed light on the complex structure of ruptures in the area of the Mogod earthquake epicenter, within which three segments differing in the displacement amplitudes and kinematics have been identified. The research data indicate the repeated activation of the Tulet and Hulzhin Gol faults in the Late Pleistocene–Holocene. The absolute age of the latest activation is 596–994 AD for the Tulet fault and 11,379–6235 BC for the Hulzhin Gol fault. The cumulative deformation from paleoearthquakes in the trench sections in the Tulet fault zone points to at least two displacements of thrust kinematics, with the latest of them having an amplitude of 2.8 m. The paleoearthquake in the Hulzhin Gol fault zone is characterized by the presence of lateral slip. The amplitudes of deformations attest to earlier earthquakes similar in energy to the 1967 Mogod event or even stronger in the fault node. The obtained data on the timing of these earthquakes and the amplitudes of the accompanying displacements made it possible to estimate slip rates along the faults: 0.2–0.3 m/kyr horizontal-slip rates on the Hulzhin Gol fault and 0.5–0.7 m/kyr vertical-slip rates on the Tulet fault.

The article presents the results of the first integrated geological and geophysical studies of the Sarma paleoseismic dislocation (PSD). Based on interpretation of sections of trench walls, analysis of shallow geophysics data (electric survey, seismic survey, ground-penetrating radar), and morphological profiling of microforms of the seismogenic relief, a conclusion has been reached on transpressional deformations. The displacement planes of the main reverse faults and thrusts dip to the northwest; minor ones, to the southeast. The kinematic characteristics of seismic movements indicate the formation of dislocations in the Primorsky fault zone under subhorizontal compression conditions.

—The paper presents results of a seismogeological study based on analysis of seismic data and historical facts about the seismic activity of the Khambinskii fault zone. According to the data obtained, a genetic type of dislocations on conjugate faults (Gusinoe Ozero and Orongoi paleoseismogenic structures) is related to reverse faults with a strike-slip component. Geophysical studies of the Gusinoe Ozero structure have determined the dip of the fault plane toward the mountain framing of the depression and its outcrop at the bottom of the seismic scarp. The significant seismic potential of the Khambinskii fault is responsible for the maximum intensity of shocks in the nearby cities and settlements of southeastern Transbaikalia. The seismic fault activity has been confirmed by the historical earthquakes of 1856 and 1885, the M = 5 earthquake that occurred on 2 October 1980, and at least two prehistoric earthquakes. The latest of the latter occurred no earlier than ~4 ka and had M = 7.0–7.3, while the earliest was even more intense and took place in the first half of the Holocene, no later than ~6 ka.

Seismotectonic deformation and crustal stress pattern have been studied comprehensively in major seismogenic structures of the Kharaulakh sector of the Verkhoyansk fold system and adjacent parts of the Chersky seismotectonic zone. The study focuses on neotectonic structures, deep structure, and systems of active faults, as well as tectonic stress fields inferred by tectonophysical analysis of Late Cenozoic faults and folds. The results, along with geological and geophysical data, reveal main strain directions and structural patterns of crustal stress and strain in the Arctic segment of the Eurasia-North America plate boundary. The area is a junction of mid-ocean and continental structures evolving in a mixed setting of extension, compression, and their various combinations. The rotation pole of the two plates is presumably located near Buor-Khaya Bay. In this case, extension is expected to act currently upon the neotectonic structures north of the bay and compression to control those in the south and southeast. This inference is consistent with the identified zoning of stress and strain in the Kharaulakh sector. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Based on the analysis of space images and maps, the data of laser scanning, trenching, and field geophysical and seismotectonic studies in southern Yakutia, the Chulmakan seismogenic fault is mapped and characterized. The structure and parameters of seismogenic deformations of this fault, which crosses the Power of Siberia gas pipeline, are determined. A preliminary estimate of the Chulmakan seismodislocation age is given, as well as the magnitude of the corresponding paleoearthquake. The level of potential seismic hazard at the site where the Chulmakan Fault crosses the East Siberia–Pacific Ocean oil pipeline and Power of Siberia gas pipeline is determined.

The paper presents results of seismogeological studies of active faults bordering the Upper Kerulen basin, one of the largest intermountain basins of the Khentei upland. Morphometric and trenching methods were applied to estimate the main parameters of seismogenic dislocations and associated Holocene palaeoearthquakes (540–2810, 3170–3720, and 7480–9220 years ago). The maximum palaeoearthquake magnitude (7.5) characterizes the seismic capacity of the potential focal area (PFA) confined to the Kerulen fault. The new data show the need to revise the potential seismicity concepts of the southern Khentey area and to make appropriate changes in the general seismic zoning maps. The relationship between the dislocations and the modern topography features, as well as deformation of the subsurface sediments in the studied mine openings give evidence of thrusting under the sub-lateral to north-western subhorizontal compression.

The results of paleoseismological investigations to find the epicentral area of the Belovodskoe earthquake are presented. New data on prehistoric earthquakes have been obtained resulting from a seismic deformation study using trenching. It is found that seismic dislocations during the reactivation of the fault by the 1885 earthquake did not extend east of the Sokuluk River. In addition, the age and kinematic features of a paleoearthquake located in the area between the Sokuluk and Alamedin rivers are specified. This earthquake occurred in the interval of 887–1533 cal BC and was no less than 7.1 in magnitude. The minimal estimated earthquake source length is 32 km and the reverse-fault amplitude is 3.8 m.

The paper reviews goals and objectives, stages and the content of seismotectonic studies conducted in Eastern Siberia. Such studies are based on a comprehensive analysis of geological and geophysical data and provide for establishing whether the local earthquakes are of tectonic origin and revealing their relationships with recent geodynamic processes in the area under study. Seismic hazard assessment and evaluation of tectonic processes are the two major, closely interrelated aspects of seismotectonic studies. The latter are generally conducted in combination with seismic studies prior to the stage of detailed seismic zonation (DSZ) which is followed by seismic micro-zonation (SMZ). In three stages of seismotectonic studies, we analyse specific geological structures, reveal the regional dynamics of seismotectonic processes, clarify details of potential seismic hazard locations and identify sites of the potential instantaneous deformation of the crust which may take place due to active faulting. Based on results of the long-term studies conducted by the authors, a seismotectonic map of Eastern Siberia is compiled. The paper briefly reviews the methods of mapping and refers to data on active faults and neotectonic structures revealed in the area under study, which are closely related to regional earthquake sources.

НОВЫЕ ГЕОЛОГО-ГЕОФИЗИЧЕСКИЕ ДАННЫЕ ДЛЯ ОЦЕНКИ СЕЙСМИЧЕСКОЙ ОПАСНОСТИ СТОЛИЦЫ МОНГОЛИИ О.П.Смекалин 1

In recent years, the Hustai, Gunji, and Kerulen paleoseismogenic structures have been discovered and examined within the Henteyn uplift. Their investigations revealed zones of probable earthquake foci, presenting a seismic hazard for Ulaanbaatar. We report the first data on the quantitative parameters of prehistoric earthquakes in the Meso-Cenozoic Upper Kerulen basin. The absolute age of two paleoevents determined by radiocarbon dating is within 1152-1702 BC and 5466-7201 BC. Seismogeological study of dislocations made it possible to estimate the type of tectonic stress during the formation of structures within the Henteyn uplift and to explain their nature. The horizontal-compression stress is mostly due to endogenous processes, which lead to the enlargement of the uplift area at the expense of the peripheral Mesozoic sedimentary basins. (C) 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The paper reviews goals and objectives, stages and components of a seismotectonic study conducted in Eastern Siberia, Russia. Based on a comprehensive analysis of geological and geophysical data, our study establishes whether the local earthquakes are of tectonic origin and reveals relationships among earthquakes with recent geodynamic processes in the area under study. Seismic hazard assessment and evaluation of tectonic processes are the two major closely interrelated aspects of seismotectonic studies. A seismotectonic study is generally combined with a seismic study and conducted prior to the stage of detailed seismic zonation (DSZ) which is followed by seismic micro-zonation (SMZ). In three stages of the seismotectonic study, we analyze specific geological structures, reveal the regional dynamics of seismotectonic processes, clarify details of potential seismic hazard locations and identify sites of the potential instantaneous deformation of the crust which may take place due to active faulting. Based on results of our longterm studies, a seismotectonic zonation map of Eastern Siberia is compiled. The paper briefly reviews the methods of mapping and refers to data on active faults and neotectonic structures revealed in the area under study, which are closely related to regional earthquake sources.

The results of the field seismogeological studies in the Klichka thrust zone, southeastern Transbaikalia, are considered in this paper. This territory in the contemporary epicentral field is characterized by weak earthquakes that do not reflect the true seismic potential. The seismotectonic dislocations, corresponding in their parameters to fault-forming earthquakes with magnitude of 6.0–7.2, are revealed in the southwestern flank of the Klichka thrust. Radiocarbon dating of the paleoevents and historical-archaeological data indicate that the age of the oldest events registered during the field works is 9300 years ago (M = 7.2). An earthquake with M ≈ 6.5 occurred 7000 years later, sometime in the 1st to 11th centuries. The third paleoearthquake with M ≈ 6.0 occurred in the 12th to 18th centuries.

The recent geological, geophysical, and paleoseismic research of the Hustai, Emeelt, and Gunjiin active seismogenic faults in the vicinity of Ulaanbaatar provided evidence of prehistoric seismic events there. In particular, dislocations of two fault-forming paleo-earthquakes were revealed in the Gunjiin tectonic zone. The shocks occurred in the Late Pleistocene-Early Holocene. The presence of ruptures, initially identified by morphological characteristics, was proven by trenching studies and materials of geophysical profiles. The magnitudes of the ancient earthquakes are estimated to be 6.5–7.0. The obtained results provide grounds for reassessment of the possible level of seismic hazards for the territory of Ulaanbaatar to at least 8.