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This paper presents the results of a detailed study of two relatively strong seismic events, occurred on November, 22, 2016 (МW = 5.0) and April 3, 2017 (МW = 4.8) at the northeastern flank of the Baikal rift zone in the areas of the South Muya and Kalar ranges. Both the events were followed by weak aftershocks (N = 178–539, Кр ≤ 11.0), whose epicenters were densely distributed over an area. The seismic moment tensors and hypocentral depths of the mainshocks were calculated from surface wave amplitude spectra. It has been shown that their sources were formed under the influence of the subhorizontal SE–NW extension and the subhorizontal or inclined NE–SW compression. Both the earthquakes were followed by noticeable macroseismic effects at epicentral distances up to 500 km. In the area of the Baikal−Amur Railway, their shaking intensity was IV–V MSK-64. The results obtained can be used in continuous seismic monitoring at the northeastern flank of the Baikal rift zone and can contribute to an objective seismic hazard assessment of the study area. [ABSTRACT FROM AUTHOR]

Abstract—The MW = 6.7, ML = 6.9 Khuvsgul (Khubsugul, Khövsgöl) earthquake occurred on January 12, 2021 in the Northern Mongolia close to the border of Russia. The earthquake caused ground shaking which reached intensity IX at the epicenter and was perceptible in the cities and villages of the Eastern and Western Siberia. The earthquake occurred in the region of the same-name fault and caused intense aftershock process on a segment between two fault's bends. The fault segment encompassed by the aftershocks goes from the lake to the northwest. Seismic activation has involved a segment of the boundary of the ancient Tuva–Mongolian microcontinent hosting the parallel Khuvsugul and Darkhat rift depressions and the Busingol rift depression consisting of three linearly elongated troughs. Until the present, the region of the Busingol depression was distinguished by high seismicity, whereas the regions of the Darkhat and Khuvsgul depressions were characterized by moderate and low seismicity, respectively. The earthquake of 2021 is the largest earthquake that occurred on the Khuvsgul fault over the entire history. In less than two months, the level of the frequency–magnitude graph for the aftershocks has exceeded the level of the annual frequency–magnitude graph of the earthquakes for the Altai–Sayan mountain region. The aftershock density is nonuniformly distributed along the fault; the structure of the distribution is correlated to the unilateral block structure of the Earth's crust east of the activated fault segment. The seismic potential of the Khuvsgul fault was estimated at Mmax = 7–7.5, and this earthquake, as suggested by the geological data, is not the maximum possible event. Given that seismic activation after the 1991 Busingol earthquake has not yet ceased, we have two strong activations in the Tuva–Mongolian block which can significantly affect evolution of its seismicity. [ABSTRACT FROM AUTHOR]

In this article we consider the animal behavior caused by seismic effects of the relatively strong (Mw = 5.5) Bystraya earthquake of September 21, 2020, in the southern Baikal region. The information has been obtained using the online questionnaire available on the website of the Baikal Branch of the Geophysical Survey, Russian Academy of Sciences; as a result, the amount of macroseismic data was much larger than was previously possible. In total, 3012 questionnaires were collected, of which 1169 (42.71%) reports contained some information about animal behavior before, during, and after the earthquake. There is a wide variety of domestic animals mentioned in eyewitness reports; however, the reports on dogs, cats, and parrots are the most representative and statistically significant. An analysis of the data allows us to assess the ratio of animals that reacted to the earthquake and were insensitive to it, and also determine the main types of seismically induced anomalous animal behavior. Abnormal animal behavior was noted in the period from several hours to several minutes before the quake, and the number of the reports on animal reactions prior to the seismic event noticeably exceeds the statistical error. The most pronounced reaction of animals was observed directly at the moment of the earthquake. Animal reactions became apparent at shaking intensity I = IV MSK-64; this intensity can be considered the threshold value. We also assume that the animal reactions to the seismic effects may depend on the presence of a low-frequency underground hum during an earthquake. Our research is the first experience in analyzing seismically induced animal behavior for the southern Baikal region and can be used for identifying short-term biological earthquake precursors. [ABSTRACT FROM AUTHOR]

This paper considers the September 28, 2019 earthquake that occurred on the northeastern flank of the Baikal Rift Zone (BRZ), called the Lenger earthquake after its location. The seismic moment tensor and hypocentral depth of the event are calculated from data on surface wave amplitude spectra with additional information on P-wave first-arrival polarities recorded at regional stations. The hypocentral depth is 11–12 km, the moment magnitude Mw = 5.1, and the scalar seismic moment M0 = 5 × 1016 N m. The earthquake source is formed under the influence of horizontal submeridional extension and subhorizontal NE–SW compression. The latter approximately coincides with the azimuth of the fast S-wave velocity in the upper mantle obtained from SKS-splitting and surface wave tomography data. The Lenger earthquake was felt at epicentral distances of more than 600 km. Comparison of its macroseismic effects with effects of other strong seismic events in the study area demonstrates that the regional macroseismic field equation should be actualized for the territory of the northeastern flank of the BRZ. Analysis of the obtained data, along with the available information on the stress-strain field of the crust of this area indicates that the geodynamical pattern of the conjunction zone of the northeastern flank of the BRZ and the Olekma–Stanovoi orogenic system influences the low-active Transbaikalia block. However, due to low tectonic activity, the tectonic stress accumulation period sufficient for the occurrence of relatively strong seismic events is larger than in regions with high-level tectonic activity. [ABSTRACT FROM AUTHOR]

The area of western Transbaikalia is characterized by moderate seismic activity. Nevertheless, there is historical and instrumental evidence to show that rather strong seismic events have occurred in the area and caused considerable material damage to the population centers around their epicenters. Seismological knowledge of the region is scant. The earthquake catalogs for the area and for the historical period of time need to be corrected and supplemented. The present paper considers the earthquake of October 9, 1864, which has not been included in any parametric catalog thus far. New primary data that were found in the regional periodic press were used to determine the epicenter and magnitude (M = 5.1) for the event. The earthquake of October 9, 1864 is a 'forgotten' event, but is a significant addition to the catalog for western Transbaikalia. The materials presented here can be used to assess earthquake hazard for the area, as well as to aid in the search for other unknown or 'forgotten' earthquakes. [ABSTRACT FROM AUTHOR]

Scenarios for developing focal zones of strong ( M = 5.3) earthquakes that occurred in the Middle Baikal region in 2008 and 2011 are considered. The new (submeridional and sublatitudinal) lines of destruction of the Earth's crust in the water area of the lake are recorded. The facts of seismoactive structures forming in the surrounding mountains (to the southeast) under typical rift conditions of movements are established, which indicates that the basin of Lake Baikal is expanding and growing due to active capturing and processing of its mountain surroundings. [ABSTRACT FROM AUTHOR]

The results of detailed studies of the January 6, 2006, Balei earthquake ( K = 13.1, M = 4.7 [7]), which occurred in an almost aseismic area of the east Trans-Baikal Region, are presented. The focal mechanism and dynamical characteristics of the focus are considered, and the structural-tectonic position of the focus is analyzed. It is supposed that the focus of this seismic event coincides with an activated segment of the northwest-striking Balei-Darasun fault. The maximal observed macroseismic intensity was 5-6 points by the MSK-64 scale (in the town of Baleis). The origination of foci for the earthquake with such intensity and magnitude takes place substantially owing to subhorizontal northeastern compression, the varied-rank block structure of the medium, and low rate values of tectonic motions; on aggregate, all these factors promote the accumulation of stresses in the Earth's crust. The obtained data can be useful for the purpose of assessment in seismic danger of the region. [ABSTRACT FROM AUTHOR]