This paper examines areas of seismic activity in Southern Siberia. It is shown that the potential earthquake source (PES) zone model created for the general seismic zoning does not fully correspond to the data on the seismic activity of the region. For seismic stations at and near hydroelectric dams, a study of seismograms of large earthquakes from different epicentral zones of natural seismicity, as well as records of the largest man-made earthquakes in the region, has been carried out. Attention is paid to platform earthquakes in the areas of hydroelectric power stations. Current power spectra are studied, which show the level of influence of signals against the background of industrial noise and microseisms, and the frequency composition and duration of seismic vibrations of dams during different earthquakes is determined. This work is the first step towards assessing the impacts of earthquakes from the most active epicentral zones on hydroelectric power stations in Siberia, taking into account the real characteristics of the signals. The level of seismic effect of industrial explosions in the region is considered. The research is aimed at clarifying and improving seismic zoning in the areas where hydropower structures are located in Southern Siberia.

-Years after the Chuya earthquake of 2003, geological structures adjacent to the focal area of the Chuya earthquake are still seismically active. The Aigulak focal area is one of them, but energetically the most pronounced. Detailed studies have been carried out with the network of stations of the Altai seismological testing site, supplemented by temporary stations. The region activated in the form of a local and compact structure measuring 10 x 10 km with focal depths from the first 100 m to 20 km. The focal area is not a subsequent activation along the same fault with the Chuya earthquake, but is located on a subparallel fault in the nodal region with its branching into three faults. The seismic activation of the Aigulak focal area is not an aftershock process after a major earthquake, but is an activated structure with a dynamically changing seismic process. An intensive process has formed since the earthquake in 2012 with ML = 6.1 with a gradual decrease in the number of earthquakes, and in 2019 the Aigulak earthquake with ML = 5.5 occurred with a very strong aftershock process after it. Our results of an area study of earthquake density in the focal zone indicate a change in the regime over time: from chaotic to self-organizing along short faults. We conclude that the focal area has not reached the maximum level of seismic energy release.

An analysis of the seismicity of the Altai-Sayan region in 2020 is given. The stationary seismic network in the reporting period consisted of 53 registration points, work was carried out on the modernization and retrofitting of recording equipment. In addition to the stationary network, four local time networks functioned in the region: one investigated the seismic process and accumulated data for constructing the Moho boundary using the method of receiving functions in the Altai Republic, the other three recorded man-made seismic processes in the area of coal mining enterprises in Kuzbass and the Novosibirsk region. In 2020 8438 earthquakes have been registered in the region, 4655 of them occurred in the Chui-Kurai zone of the Altai Mountains, for which a separate overview of seismicity is presented. The total seismic energy released in the earthquake foci of the Altai-Sayan region in 2020 amounted to 2.191012 J, which is a record low value in the entire history of instrumental observa tions. The slope of the linear part of the earthquake recurrence graph for 2020 has not undergone significant changes compared to the previous reporting period. The strongest in 2020 earthquake in the region (ML=5.3) occurred on October 22 at 13h38m on the southern slope of the Eastern Sayan ridge.

This paper is concerned with the influence of the large (ML = 6.9) 2021 Hubsugul earthquake on the seismicity of the block structure in the junction area between the Altai–Sayan mountain region and the Baikal Rift Zone. This study uses data from the networks of seismic stations operated by the Altai–Sayan and Baikal branches of the RAS Geophysical Survey, as well as from Mongolian stations. We show the evolution of the seismic process near the boundaries of the Tuva–Mongolia block and adjacent blocks in eastern Tuva. We have determined and studied the source zone of the Darkhad earthquake swarm which was formed in 2022‒2023 as several sequences of events, with the larger ones having magnitudes ML > 5. Simultaneously with the activation of the Hubsugul earthquake source zone, we observed high seismic activity in the source zones of past large earthuuakes: 1991 Busingol, 2011‒2012 Tuva events, and 2008 Belin-Bii-Kham. The action of the Hubsugul earthquake on the seismicity in boundary blocks of the Altai–Sayan and Baikal zones was different from that of the 2003 Chuya earthquake on Altai seismicity.

The seismicity of the Altai-Sayan region in 2018–2019 is considered. The stationary seismic network within the reporting period consisted of 55 stations. Upgrading the recording equipment and retrofitting the stations with strong motion sensors was continued. In addition to the stationary network, five local networks functioned in the region. One of them investigated the seismic process and accumulated data for constructing the Moho boundary using the method of receiving functions in the Altai Republic, the other four were focused on the study of technogenic seismicity in the area of coal minings of the Kemerovo and Novosibirsk regions. During the reporting period, 15405 earthquakes were registered in the region, 52 % of them occurred in the Chui-Kurai zone of the Altai Mountains, for which a brief description of seismicity is given separately. The total seismic energy released in earthquake foci was 2.191012 J in 2018 and 1.171013 J in 2019. The slope of the linear part of the earthquake recurrence chart for 2018–2019 has not undergone significant changes compared to previous reporting periods. The largest earthquake on the territory of the Altai-Sayan region for the reporting period (ML=6.2) occurred on February 1, 2019 at 21h54m in China, 70 km south of the Zaisan lake

The paper presents the studies of the Khuvsgul earthquake on January 11, 2021 at 21:32 UTC (January 12, 2021 at 05:32 local time), M W = 6.7, M L = 6.9, and the seismicity structure in the aftershock period for the Altai-Sayan mountain region and the Baikal rift zone, where the epicenter of this earthquake was located. Two faults are seismically activated, diverging from the southern end of the aftershock area at an acute angle: one in the northeast and one in the northwest direction, as well as transverse faults between them. According to the epicenter position and studies of the source area by other authors, the main event corresponds to the northeastern fault, and large aftershocks occurred at the junction of the northwestern fault with transverse faults feathering from the east. The main event was immediately followed by a series of large aftershocks, the strongest of which occurred on March 31, 2021 with M L = 6.2 and on May 3, 2021 with M L = 6.4. Spatial changes in the seismic regime of the aftershock region led to the predominant activity of its southern end. The junction area of the collisional structures of the Altai–Sayan folded zone and the rift structures of the Baikal depressions system is distinguished in seismicity as a block structure with increased seismicity near the block boundaries. First of all, these are the Tuva-Mongolian block and the eastern part of the Sayano-Tuva block. After the Khuvsgul earthquake of 2021, a block structure with the activation of the epicentral zones of the 1991 Busingol earthquake, the 2011–2012 Tuva earthquakes, and other structures seismically active until 2021 has increased seismic activity. It is proved that the 2014 Khuvsgul earthquake occurred under the basin of the same name and is associated with other faults than the 2021 earthquake and is not a direct precursor of the 2021–2022 activation.

The 2003 Chuya earthquake had a noticeable impact on the seismicity of the whole Altay region. The article presents data on changes in the seismic regime of Altay from 2003 to 2021. It is shown that in the first six months after a major earthquake in 2003, earthquakes occur in the epicentral zone, and other structures of Altay are aseismic. After 2009, changes are formed both in the near zone, covering geological structures adjacent to the epicenter, such as the Aigulak, Kuray, South Chuya, North Chuya ridges, and in the far zone at distances of 250‒300 km from the epicenter and in different directions from it. After the Aigulak earthquake of 2019, an aftershock process was formed, which ensured the displacement of the center of Altay seismicity into the ridge of the same name. The explanation of the seismicity development in space and with time delays for years can be given on the basis of the influence of a large earthquake on the multi-layered lithosphere in accordance with models that assume the occurrence of disturbances during a large earthquake not only in the fragile part of the earth’s crust, but also in layers with high plasticity.

The Chuya earthquake of 2003 exerted an appreciable influence on the seismicity of the entire Altai. This paper presents data on variations in the Altai seismicity from 2003 to 2021. It is shown that earthquakes of the first half-year after the major earthquake of 2003 had their rupture zones in the epicentral zone, while the other Altai structures were aseismic. After 2009 we saw changes both in the near zone that encompasses geological structures that were adjacent to the epicenter (with distances of 60‒80 km from the mainshock epicenter), such as the Aigulak, Kurai, South Chuisky and North Chuisky mountain ranges, and in the far zone at distances of 250‒450 km from the epicenter and in different directions from it. The Aigulak earthquake of 2019 gave rise to an aftershock process that displaced the center of Altai seismicity to the eponymous mountain range. There are no data on large earthquakes during the historical period for many Altai structures which have been activated following the Chuya earthquake, either from seismological or from paleo-geological evidence. One could explain the evolution of seismicity around the rupture zone of the Chuya earthquake in space, and with time delays of some years, invoking the influence of a large earthquake on a medium involving plasticity. We know of nonlinear models that hold promise for future research concerning the influence of large earthquakes on the evolution of seismicity in geological media.

Bachat earthquake (M = 6.1) with the epicenter coordinates of 54.29 degrees N, 86.17 degrees E occurred on June, 18 2013 near the Bachatsky coal strip mine, is the world's largest earthquake induced while mining solid minerals. More than 5000 aftershocks were regis-tered and the spatial volumetric structure of the aftershock area was investigated. The Bachat coal field is located in the Salair zone of the Kuznetsk Depression and is represented by a brachysynclinal fold of a very complex structure characterized by the damage and fracturing behaviors of rocks. The main event is confined to the coal-mine pit wall, with the greatest density of aftershocks observed in its middle portion. In the cross section, aftershocks form a wide area with its deepened portion shifted towards the Kuznetsk Depression, while large faults bounding the depression dip down under the Salair Ridge. In the exposed pit wall, at a depth of 4 km, the activated area resembles a rhombus whose horizontal diagonal line runs across the entire length of the mine pit and decreases both in upward and downward direc-tions. The area is seismically activated to a depth of 6 km, with more intense activation of rock mass observed within the 1-3 km depth interval. Results of the study of the mechanisms of aftershock sources revealed a disagreement between the stress state of rock mass of the Bachatsky open-pit coal mine modeled from the mechanisms of aftershocks, and the mainshock mechanism of the Bachat earthquake.

Бачатское землетрясение 18.06.2013 г. с магнитудой ML = 6.1, с координатами эпицентра 54.29° с.ш., 86.17° в.д. произошло около одноименного угольного разреза. Оно является крупнейшим в мире техногенным землетрясением при добыче твердых полезных ископаемых. Зарегистрировано около 5000 афтершоков, рассмотрена структура афтершоковой области. Бачатское угольное месторождение находится в Присалаирской зоне Кузнецкой впадины и структурно является брахисинклиналью очень сложного строения с высокой степенью нарушенности и трещиноватости пород. Главное событие приурочено к борту разреза, а наибольшая плотность афтершоков наблюдается в его центральной части. В поперечном разрезе афтершоки образуют широкую область со смещением ее заглубленной части в сторону Кузнецкой впадины, в то время как ограничивающие впадину крупные разломы имеют наклон под Салаирский кряж. В срезе вдоль угольной выработки активизированная область похожа на ромб с горизонтальной диагональю на глубине 4 км на всю длину разреза и с уменьшением активизированной области в верхнем и нижнем направлениях. Активизирована область на глубину до 6 км, наблюдается локальная по размерам усиленная активизация недр на глубинах 1-3 км. На основе изучения очагов афтершоков обнаружено, что напряженное состояние недр Бачатского разреза, восстановленное по афтершокам, не соответствует механизму главного события. The Bachat earthquake ( M = 6.1) with the epicenter coordinates of 54.29° N, 86.17° E occurred on June, 18 2013 near the Bachatsky coal strip mine, is the world’s largest earthquake induced while mining solid minerals. More than 5000 aftershocks were registered and the spatial volumetric structure of the aftershock area was investigated. The Bachat coal field is located in the Salair zone of the Kuznetsk Depression and is represented by a brachysynclinal fold of a very complex structure characterized by the damage and fracturing behaviors of rocks. The main event is confined to the coal-mine pit wall, with the greatest density of aftershocks observed in its middle portion. In the cross section, aftershocks form a wide area with its deepened portion shifted towards the Kuznetsk Depression, while large faults bounding the depression dip down under the Salair Ridge. In the exposed pit wall, at a depth of 4 km, the activated area resembles a rhombus whose horizontal diagonal line runs across the entire length of the mine pit and decreases both in upward and downward directions. The area is seismically activated to a depth of 6 km, with more intense activation of rock mass observed within the 1-3 km depth interval. Results of the study of the mechanisms of aftershock sources revealed a disagreement between the stress state of rock mass of the Bachatsky open-pit coal mine modeled from the mechanisms of aftershocks, and the mainshock mechanism of the Bachat earthquake.

The results of an experimental study of seismic vibrations at the site for the construction of the Siberian Ring Photon Source (SKIF), which is a synchrotron radiation source of the fourth plus generation at 3 GeV and a perimeter of 480 m, have been considered. Seismic vibrations are a hindrance that reduces the accuracy of the experimental setup when studying materials with precision accuracy and resolution. The experiment was performed with broadband seismological equipment used at seismological stations. Seismic vibrations from different types of sources have been investigated: natural and man-made earthquakes, industrial explosions, noises of automobile and railway transport, vibrations from industrial equipment at enterprises located away from the facility under construction. Natural earthquakes create the strongest broadband impact on the site. Man-made earthquakes in the area of the Gorlovka coal basin can create short-term strong seismic impacts. Industrial explosions in terms of the seismic impact on the site are significantly inferior to the effects of earthquakes and are characterized by a more limited spectral composition of vibrations. The noises of motor transport cover frequencies from 4 to 30 Hz and quickly fade away along the site with distance from the road. Railway noises have the characteristic appearance of a set of multiple harmonics covering a wide frequency range with a duration of up to 10 min. Monochromatic signals from the operation of industrial equipment on and off the site are recorded at the site. At the same time, both continuous signals and those that occur episodically are recorded. A special class consists of monochromatic oscillations with a slowly varying frequency. The information on the level, spectrum, and duration of seismic vibrations necessary for calculating the seismic protection of the SKIF Central Research Center during its creation and development of a seismological monitoring system that compensates for the seismic effect on the accuracy of experiments was obtained.

The characteristic features of the seismicity of the Altai-Sayan region in 2016–2017 are considered. The stationary seismic network within the reporting period consisted of 52 stations. Upgrading the recording equipment and retrofitting the stations with strong motion sensors was continued. In addition to the stationary network, four local time networks functioned in the region. One of them investigated the seismic process and accumulated data for constructing the Moho boundary using the method of receiving functions in the Altai Republic, the other three were focused on the study of technogenic seismicity in the area of coal minings of the Kemerovo and Novosibirsk regions. During the reporting period, 11424 earthquakes were registered in the region, 58 % of them occurred in the Chui-Kurai zone of the Altai Mountains, for which a brief description of seismicity is given separately. The total seismic energy released in earthquake foci was 6.141012 J in 2016 and 2.381013 J in 2017. The slope of the linear part of the earthquake recurrence chart for 2016–2017 has not undergone significant changes compared to previous reporting periods. The largest earthquake on the territory of the Altai-Sayan region for the reporting period (ML=6.39) occurred on April 4, 2017 at 15h07m in the Zaisan Depression area of the Kazakhstan Republic.

—The 2003 Chuya earthquake aftershocks are studied using the data obtained during experiments with dense networks of stations. Density maps of the foci of more than 50,000 aftershocks are compared with the day surface faults and the block structure and tectonics of the focal area. The large shearing strain caused by the Chuya earthquake is accompanied by a spatially intermittent aftershock structure stretching along it. The density maps of long-lasted aftershocks differ in structure from the maps of seismic activity in the initial aftershock area. The study has revealed a relationship between the block structure of the epicentral area and the structure of the aftershock process. The nodes of the intersection of faults with the aftershock area are characterized by reduced aftershock activity. The aftershock process is only partly confined to the block-separating faults. In many cases, the aftershock process is shifted relative to these faults or wanders from them.

n Erratum to this paper has been published: https://doi.org/10.1134/S1069351322100019

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.

Хубсугульское землетрясение 12.01.2021 г. с ML = 6.9 и глубиной очага порядка 8 км произошло в Северной Монголии недалеко от границы с Российской Федерацией на восточной границе Тувино-Монгольского блока и вызвало интенсивный афтершоковый процесс. Данный блок испытывает поднятие и одновременно к нему приурочены рифтовые впадины [6, 7, 10]. Столь сильного землетрясения в районе западного фланга оз. Хубсугул до сих пор не происходило. Землетрясение произошло в районе одноименного разлома и вызвало интенсивный афтершоковый процесс на участке между двумя изломами. Сейсмический потенциал Хубсугульского разлома оценивался в MMax = 7-7.5 [5], и данное землетрясение в соответствии с геологическими данными не является максимально возможным. Охваченный афтершоками участок разлома уходит от озера в северо-западном направлении. Сейсмически активизирован участок границы древнего ТувиноМонгольского микроконтинента. Учитывая, что сейсмическая активизация после Бусингольского землетрясения 1991 года еще не завершилась, в Тувино-Монгольском блоке наблюдаются две сильные активизации, способные оказать значимое влияние на эволюцию его сейсмичности

Based on the results of monitoring with a temporary seismic network in the southern Kuzbass in an area of technogenic seismic activation that formed during simultaneous impact of open and underground coal mining, the article presents a detailed study of the spatial structure of this activation, its development over time, and its relationship with tectonic faulting. Seismic activation near underground workings is differs in the locality of the area and a large number of earthquakes with local magnitudes of ML ≤ 2 (Bormann, 2002). For three closely located coal mines, general seismic activation is observed, within which, as a local zone, there is activation of underground workings characterized by strong earthquakes with ML = 3–4. The focal depths have a bimodal distribution with maxima in the 1–1.5 and 2–3 km ranges. Both in the area of underground mines and open mines, the deep interior is seismically activated much deeper than mining works, while the seismic process is unsteady and pulsating in time.