A B S T R A C TUnderstanding the causal relationships between tectonic earthquakes and volcanic eruptions is of particular importance for developing more effective approaches to volcanic hazard assessment. A large tectonic earthquake is believed to trigger a wide range of volcanic phenomena, including direct eruption, increased seismicity and degassing, and changes in the style of an ongoing eruption. This study examines the responses of eight volcanic systems of the Kamchatka Peninsula (Arik, Asacha, Avachinsky, Gorely, Klyuchevskoy, Ksudach, Krasheninnikov, Mutnovsky) to the Mw 8.8 mega-earthquake of 29 July 2025, based on seismic data and the Statistical Estimation of Seismicity Level (SESL’09) method. The probability that the observed volcanic phenomena occurred randomly within the temporal window of the mega-earthquake is evaluated. Possible mechanisms responsible for the responses of the considered volcanic systems are also discussed.

In October 2023, Klyuchevskoy volcano (Kamchatka, Russia) erupted, when the height of the ash column reached ~15 km. The eruption was preceded by seismic activity. The dynamics of seismicity in the four most seismically active volumes of the subsoil beneath Klyuchevskoy volcano in the depth range of 4 km above sea level and up to 34 km was analyzed using the “Statistical Estimate of Seismicity Level” methodology – SESL’09. The most pronounced increase in seismicity with an exit to high and extremely high levels was manifested at a depth of 5–8 km 1–3 months before the appearance of lava in the crater of the volcano. The precursor effect detected 1–3 months before the eruption was caused by the redistribution of stresses in the medium containing the feeding magmatic system, the pressure in which varies depending on the conditions of accumulation or supply of magma. After the culmination phase of the eruption, seismic activity at depths of more than 20 km reached an extremely high level. This may be related to the end of the eruption.

The seismicity review of Kamchatka and surrounding territories for 2020 is given. In the Kam chatka earthquake catalogue, the minimum local magnitude of completeness is MLmin=3.5, and for the Kamchatka seismically active region (=50.5–56.5° N, =156.5–167° E) MLmin=3.0, and for earthquakes with h≥350 km under the Okhotsk sea MLmin=4.1. The Kamchatka earthquake catalogue for 2020, published in the Appendix to this article, includes 1666 events with ML≥3.5; 94 earthquakes with ML=3.55–7.65 were felt in Kamchatka and sur rounding areas with seismic intensity I of 1–2 to 6–7 according to the Seismic Intensity Scale-2017 (Russian state standard). For 49 events with ML≥5.0 that occurred in 2020 within the area of responsibility of Кamchatka branch of Geophysical Survey RAS, an attempt to calculate the seismic moment tensor (SMT) was made. The level of seismicity according to the "SOUS'09" scale in 2020 corresponded to the “high”. On March 25, 2020, there was a strong earthquake with Mw=7.4, named “the Paramushirskoe earthquake”. The earthquake was accompanied by a large number of aftershocks.

The concentration of major ions ( HCO_3^ - , Cl–, SO_4^2 - , Ca2+, Mg2+, Na+, and K+) in the water of tributaries of Lake Teletskoe (Northeastern Altai) was studied in 2016–2020. Seasonal variations were found in the ion composition of the water of lake tributaries and a relationship between this composition and the biogeochemical conditions in their drainage basins was established. The waters of eastern and western tributaries, which drain shores with different geological and landscape structure, differ in both the concentrations and proportions of the major ions. It is shown that most of the examined tributaries belong to the same hydrogeochemical facies and carry water of bicarbonate-magnesium-calcium type. Characteristics of ion runoff of three lake tributaries were calculated; chemical denudation in their drainage basins was evaluated.

The article presents instrumental and macroseismic data on the Paramushir earthquake of March 25, 2020, ML=7.7, Mw=7.4, discusses its tectonic position and features of the aftershock process. This event is the strongest instrumentally recorded earthquake with a source located in the Pacific lithospheric plate in the area of the Northern Kuril Islands. The focal mechanisms and moment magnitude values Mw of the Paramushir earthquake and its strongest aftershocks were obtained using an original method for calculating seismic moment tensors, de veloped at the Кamchatka branch of Geophysical Survey RAS. The Paramushir earthquake was felt in 60 settle ments in the Kamchatka and the Sakhalin Regions, and was also noticed on the islands of Hokkaido (Japan) and Adak (USA). The maximum macroseismic manifestations were noted in the city of Severo-Kurilsk (Paramushir Island), I=6–7 points on the Seismic Intensity Scale 2017 (Russian building code GOST R 57546–2017); there were no casualties or destruction. A weak tsunami with a maximum observed wave height of ~50 cm was noted in the area of Severo-Kurilsk.

The Tonga‒Kermadec subduction zone is located between the Pacific and Australian plates and is the site of the highest rates of Pacific plate subduction and dominant extension. In 2006 and 2009 in this region, two strong earthquakes occurred with magnitudes Mw = 8.0 and 8.1. There are about 170 islands in the Tonga region. They are volcanic centers that have erupted regularly over the past few decades. The paper presents the results of determining temporal variations in the slope of the earthquakes recurrence curve (b-value) in the Tonga subduction zone for 2005–2022 and variations in b depending on depth. Temporal variations in the b-value reflect the general tendency for the most powerful earthquakes to occur against the background of a decrease in b-value only in the surface layer at depths of 0–100 km. By comparing the variation of b-value with depth with a tectonic model of the Tonga subduction zone, it suggested that lower b-value might reflect greater stress at the top of the subducted slab due to its bending. Elevated b-value can apparently be associated with stretching mechanisms. For the Tonga subduction zone, as for other subduction zones, the increased b-value identified at a depth of 90‒100 km, which may be due to the presence at this depth of a magmatic front, which is associated with active volcanism.

The Tonga-Kermadec subduction zone lies between the Pacific and Australian plates. The location shows the highest rate of subduction for the Pacific plate and a dominant tension. Two great earthquakes occurred in the region in 2006 and 2009 whose magnitudes were Mw = 8.0 and 8.1. There are about 170 islands around the Tonga subduction zone; these islands are volcanic centers that have been regularly in eruption during the last several decades. The present study presents the results from the determination of time-dependent variations in the slope of the recurrence curve (the b-value) at the Tonga subduction zone during 2005–2022, and depth-dependent variations in b. The time-dependent variations in b reflect the general tendency of great earthquakes occurring upon the background of lower b-values in the surface layer only, at depths of 0–100 km. The comparison between the depth-dependent variations in b and the tectonic model for the Toga subduction zone implies the hypothesis that lower b-values may reflect greater stresses in the upper part of the plunging plate due to its bending. Higher b-values seem to be connected to tensional mechanisms. A region of higher b-values at depths of 90–100 km has been identified for the Tonga subduction zone, as well as for other subduction zones, which can be related to the presence of a magmatic front at these depths, which is related to active volcanism.

The aim of the study was to assess ecological, biogeochemical and sanitary-hygienic aspects of arable soils of the Altai region and spring wheat grain produced there. Location and time of the study. The representative study sites of arable land were located in various agroecological zones of the Altai region: Kulundinskaya (dry steppe on chestnut soils of the Kulunda lowland), Rubtsovskoye (arid steppe on chernozems of the southern Priobskoye plateau), Zarinskaya (deciduous forests and steppe meadows on leached chernozems of the Bie-Chumyshskaya elevated plain and podzolized chernozems and dark gray forest soils of the Salair Foothills), Piedmont (meadow steppe on the chernozems of the Prealtai Plain), Priobskaya (split steppe on ordinary chernozems of the Priobsky plateau), Aleiskaya (moderately arid steppe on ordinary chernozems of the Priobsky plateau), Biyskaya (forest steppe on leached and gray forest soils of the Bie-Chumysh Upland). The research was carried out in 2018. Methods. The content of trace elements in soils and wheat grain was determined by atomic emission and atomic absorption spectrometry according to PND F 14.1:2:4. 139; 140-98; НСАМ №450С; РД 52.24.479-95. Results. It was found that in the arable soils of the Altai region the elements, necessary for plants, animals, and humans, were contained in optimal quantities (average content of Mn 714, Zn 65, Cu 25.7, Co 12.3 mg/kg), maintaining the normal functioning of living organisms. Most toxic elements were found at the levels, comparable with average concentrations in soils of the world and with the data for uncontaminated soils in West Siberia, not exceeding the maximal permissible concentrations. The average concentrations of Cd, Pb, As and Hg in the studied soils were 0.089, 13.6, 5.0, 0.037 mg/kg, respectively. No biogeochemical province had been identified for any of the elements. The studied soils have a fairly high buffering capacity for heavy metals. The chemical elements’ content in the spring wheat grain, the main crop in the region, was close to the corresponding world data for grain. The amount of regulated substances (lead, cadmium, mercury, arsenic) meets domestic standards and the requirements of the Technical Regulations of the Customs Union "On Grain Safety". Conclusions. The arable soils of the Altai region are not contaminated with heavy metals. Trace elements such as manganese, zinc, copper, cobalt are contained in soils in optimal quantities for living organisms. However, using the grain as monofeed can result in Co deficiency in animals. The content of chemical elements is soils resulted from the initial content of elements in soil-forming parent rocks. The degree of heavy metals’ buffering by the studied arable soils, depending of the metal, ranged from medium to high.

Relevance. The need to expand and deepen the understanding of the influence of solar radiation indicators on chemical characteristics of surface water, since the dependence of hydrochemical processes on periodic changes in solar activity has so far been studied extremely poorly. In addition, special attention is paid worldwide to the study of iron content in waters of rivers and lakes. Iron increased concentrations are one of the reasons for the "brownification" of surface waters in a significant part of the Northern Hemisphere. Aim. To establish a relationship between iron content and dynamics in the waters of the tributaries of Lake Teletskoe with indicators of solar activity (sunspots number, F-index). Methods. Water samples from the tributaries of Lake Teletskoe were collected into clean new polyethylene bottles in the estuaries of the rivers, from a depth of 0.5 m during the spring-summer high water and autumn low water, in 2016–2020. Content of total and dissolved Fe in the waters was determined by the ISP-MS method and by the AAS method. We used the data on solar activity indicators from the Belgian Observatory, which are freely available. Results. The total Fe content in the rivers of Lake Teletskoe basin for the period from 2016 to 2020 changes from 5 to 340 µg/l. Concentrations of dissolved iron (4 to 200 µg/l) do not exceed Russian standards, but they are often noticeably higher than the global average for river waters established abroad. The highest iron content, as well as the proportion of its soluble forms in the tributaries of Lake Teletskoe and in lake waters, was noted in 2016. It is probably due to the highest rates of solar activity. They cause certain changes in the environment – such as an increase in air temperature and water evaporation, and decrease in river flow, which accompanied by growth in concentrations of chemical elements in surface waters. Since 2016, there has been a steady decrease in dissolved iron concentration in surface natural waters of Lake Teletskoe basin, which may be a consequence of a decrease in solar radiation intensity in recent years.

This paper describes the behavior of several seismic precursors prior to the 2016–2019 activation in an area of a complex geodynamic setting at the boundary of the Pacific, North American, and Eurasian plates. We used an integrated approach to combine identified precursors with a view to getting more accurate locations of possible rupture zones of future large earthquakes. The precursors include quiescence based on the RTL parameter and the “Z-function”, variations in the slope of the earthquake recurrence graph (γ-value), and the areas of seismic ruptures dS. For the first time in Kamchatka, we analyze anomalies in the parameter dS interpreted as seismic activations to show the presence of a precursory component before the onset of the foreshock activation. Examples include increases in the values of that parameter before events that were the largest for the areas where they occurred: the Near-Islands Aleutian earthquake of July 17, 2017, Mw = 7.8 and the Uglovoe Podnyatie earthquake of December 20, 2018, Mw = 7.3. The overall extent of the anomalous area, which still exists and includes consecutive quiescence and foreshock phases, is 900 km, which creates conditions for possible occurrence of a new great earthquake in the junction zone of the three plates with a magnitude that can exceed whatever has been recorded in the region so far.

The strong Mw = 7.4 earthquake occurred on March 25, 2020 in the region of Northern Kuril Islands, with its epicenter on the ocean side of the Kuril-Kamchatka deep-water trench, to the east from its axis. The earthquake was felt on all the Kuril Islands, South and East Kamchatka, the maximum shaking was recorded in Severo-Kurilsk with intensity I = VI–VII. Distinct tsunami wave was also registered. In the article, this earthquake and its tectonic position are discussed in the context of the seismicity of the Kuril-Kamchatka arc. The actions of duty shifts in earthquake processing are described, and a detailed description of macroseismic effects is given. The results of the analysis of peak ground motion amplitudes, focal mechanisms and models of the source, tsunami propagation features are also shown. Coseismic displacements revealed by GNSS observation data are presented and compared with model data. Peculiarities and stages of the aftershock process are discussed and the size of the source area is estimated.

The efficiency of the seismic station network on the territory of the Uda Volcanic Complex (UVC), which consists of 29 irregularly distributed instruments, was assessed. At different points of the UVC, earthquakes of different minimum energy classes were recorded with different accuracies. Calculation of the minimum energy classes for the UVC seismological network of 29 stations shows that, when the number of stations is magnified to ~30 000, such a network throughout the considered territory reliably detects earthquakes of 7.0 minimum energy classes, which corresponds to magnitudes of ~2.5. The errors in determining the earthquake epicentral coordinates in latitude (δφ) and longitude (δλ) within the network do not exceed 0.4 km. The errors in determining the depths of earthquake sources (H) in the center of such a network do not exceed 0.2 km, and within the entire territory of the UVC, 5.0 km. For these calculations, the errors in determining the travel time and propagation velocities of seismic waves were set equal to 0.1 s and 0.1 km/s, respectively, and could be both random and systematic.

In recent decades Bezymianny Volcano, Kamchatka, one of the most threatening volcanic objects of Russia, has produced an average of 1–2 short-lived, but strong, explosive–effusive eruptions per year. The most reliable source of data for identifying a precursory situation before such an eruption seems to be seismicity, with continuous data being supplied by the Kamchatka seismicity monitoring system. The formalized method developed by the present author for predicting Bezymianny eruptions based on a statistical estimation of seismicity level (SESL’09) has performed satisfactorily in real time as well, with the precursory processes before all the eight eruptions of Bezymianny in 2015–2020 being detected. Revision of all characteristics the method involves (efficiency, reliability, and validity) showed that they remained stable when new data were added. The prediction method was supplemented with a new parameter, lead time, which provides a formal procedure to estimate the expectation time for a prediction to come true.

Пространственно-временные изменения фоновой региональной сейсмичности с прогностической целью отслеживаются Лабораторией сейсмического мониторинга КФ ФИЦ ЕГС РАН по нескольким среднесрочным прогностическим методикам [5]. В данной работе речь пойдет о вариациях наклона графика повторяемости Zγ региональных землетрясений Камчатки как о параметре, позволяющем в режиме мониторинга выделять такие аномальные зоны.

Для создания научно-методической основы технологий прогноза опасных геодинамических явлений (землетрясений, извержений вулканов и пр.) необходимы методические разработки по формализации предвестников, оценке их прогностической эффективности и создание алгоритмов вероятностной оценки возникновения ожидаемого события. Ранее [3] был предложен формализованная методика вероятностного прогноза извержений вулкана Безымянный на основе применения статистической оценки уровня сейсмичности СОУС’09 [2]1 В последние десятилетия на вулкане Безымянный происходит в среднем 1–2 кратковременных, но сильных эксплозивно-эффузивных извержения в год. Так c 1999 г. по 2020 г. зафиксировано 29 таких извержений. Для вулкана Безымянный характерна слабая мелкофокусная сейсмичность, которая, в основном, связана непосредственно с извержениями или предшествует им. Наиболее надежный каталог землетрясений для этого вулкана имеется с 1999 г. На основе этих данных и были определены все характеристики прогностической методики. и ряда вспомогательных функций, характеризующих предвестниковую ситуацию. Схематично процедуру прогнозирования извержения вулкана Безымянный можно представить в виде следующих этапов: Для исследования сейсмических активизаций перед извержениями вулкана Безымянный использован каталог Ключевской группы вулканов с 1999 по 2014 гг., полученный Камчатской региональной сетью сейсмических станций [4]. Для построения оценок уровня сейсмичности из каталога были выбраны землетрясения, зафиксированные в радиусе 6 км от вершины вулкана Безымянный. Отметим, что ~98% сейсмических событий приходится на диапазон глубин до 5 км. Анализируемый массив данных имеет представительность (уровень надежной регистрации) КS = 4.0.

In this paper we present brief review of results of Kamchatka Seismic Monitoring and Earthquake Prediction System operations in the last five years. In addition, the retrospective of development of hardware, equipment and software of the System performed. The main direction in the System evolution in this period concerned the creation and modernization of data acquiring and pro-cessing methods. One of main results is creation basic informational space, that includes all pro-cesses if seismic observations, from data acquiring till exchange (including external users) of da-ta processing results. In particular, the system of data storage was deeply modernized, high-speed access to the data archive was provides, high-performance computing clusters were deployed, all seismic stations were combined in the unified network. Development algorithms and software for data processing and seismic regime controlling was continued. Creation and development of the Seismological Data Informational System (SDIS) provide the access to seismic observations re-sults for research community. The service of automatic data exchange with external users was created and incorporated in SDIS. Kamchatka Seismic Monitoring and Earthquake Prediction System in 2016-2020 allowed registering and processing over 83 thousand tectonic and volcanic earthquakes. The complex studies for seven the strongest ones were conducted. Detailed analysis showed, that magnitude of completeness for regional scale is MLc=2.5, and for local scale (for example – volcano seismic monitoring) – MLc=–0.2.

Информация о текущем состоянии сейсмичности отдельного региона является достаточно широко востребованной. В круг заинтересованных лиц входят не только члены сейсмологического сообщества, но и структуры, по роду своей деятельности связанные с мониторингом природной среды (в частности, МЧС, административные структуры). Отдельной проблемой является предоставление информации о землетрясениях населению сейсмоактивных областей. Учитывая широкий диапазон потребителей такой информации, используемые характеристики должны иметь, с одной стороны, интуитивно понятный смысл, а с другой – их определение должно опираться на количественные параметры сейсмического процесса. Традиционным решением является создание шкал, переводящих числовые показатели в качественные характеристики. Формализация данной процедуры позволяет избежать ряда неоднозначностей при описании, оценке и сравнении сейсмического режима различных пространственно-временных объемов. Например, при составлении заключений о состоянии или прогнозе сейсмической обстановки многие исследователи используют понятие «сейсмического фона». Как правило, определение «сейсмического фона» не приводится, что ведет к недоразумениям при использовании таких заключений. В государственном стандарте “Мониторинг и прогнозирование опасных геологических явлений и процессов” [1], в разделе, регламентирующем мониторинг землетрясений, присутствует понятие “уровня сейсмического фона”, как одного из требуемых параметров. Однако, в этом разделе ГОСТа лишь поясняется о чем идет речь – “о пространственно-временном распределении слабых землетрясений”, то есть определение этого понятия не введено. Таким образом, разработка шкалы уровня сейсмичности соответствует потребностям организаций, ответственных за организацию и ведение мониторинга сейсмичности, удовлетворяющего требованиям упомянутого государственного стандарта. Другая проблема связана с выбором параметра, характеризующего уровень сейсмичности. Представляется, что использование абсолютных параметров, например, таких как активность A10, выделившаяся сейсмическая энергия E и т.д., не является оправданным по ряду причин. Предлагается для характеристики уровня сейсмичности конкретной пространственновременной области использовать эмпирическую функцию распределения F суммарной выделившейся сейсмической энергии E (рис. 1). Тогда, задавая пороговые значения F и зная выделившуюся энергию E, можно сделать заключение о повышенной либо пониженной сейсмической активности региона.

—The Udina volcanic complex located in the southeastern part of the Klyuchevskoy group of volcanoes in Kamchatka remained dormant for several thousand years, but the magmatic system beneath the area may be awakening judging by seismic unrest. Seismicity in the area is characterized by data from permanent regional seismic stations and campaign local stations, as well as by data of the Kamchatka earthquake catalog. Seismic activity having nucleated at shallow depths in the vicinities of the Udina volcanoes since October 2017 may reflect a beginning cycle of volcanism. The earthquakes are mainly long-period (LP) 0.5–5 Hz events, which are commonly attributed to the movement of viscous magma and resonance phenomena in magma conduits. Such earthquakes may be a response to inputs of new magma batches to the plumbing system that feeds the volcanoes and thus may be precursors of volcanic unrest. Seismic campaigns of May–July 2018 near the Udina complex provided more rigorous constraints on earthquake coordinates and origin depths and showed that most of the earthquakes originated within 5 km beneath the Bolshaya Udina Volcano. Seismic tomographic inversion using the LOTOS code revealed a zone of high P-wave velocities, low S-wave velocities, and a high vP/vS ratio directly beneath the volcano. Such a combination of parameters typically occurs in active volcanic areas and marks intrusion of partially molten magma and/or liquid fluids. The velocity anomaly detected in 2018 is shallower than that recovered in 2014–2015. The seismic evidence, along with the available geological and geophysical data, record the movement of viscous magma related to the Udina feeding system in the middle crust, which is implicit proof for connection between the intermediate crustal and deep mantle magma sources renewed after a long lull.

Многолетняя серия работ А.А. Любушина (с соавторами или единолично) по исследованию вариаций низкочастотного сейсмического шума хорошо известна в сейсмологическом сообществе, особенно по результатам, связываемым с прогнозом сильных землетрясений. Первые публикации, где представлен анализ таких сигналов, появились в 2005-2009 гг. [4-6, 9]. Публикации последних лет автора посвящены исследованию связи сейсмического шума с неравномерностью вращения Земли [8, 11]. Ряд статей ([1, 3, 7, 8]) посвящен анализу камчатских данных, что, безусловно, представляет особый интерес для камчатских исследователей, занимающихся проблемой прогноза сильных землетрясений. Следует отметить, что разрабатываемый подход к анализу сейсмических сигналов в нетрадиционно низком диапазоне частот является уникальным опытом авторского коллектива, возглавляемого А.А. Любушиным, и результаты этой продолжительной работы стимулируют широкое применение такого подхода в сейсмологической практике вплоть до рутинной обработки. Именно по этой причине хотелось бы остановиться на кондиционности исходных данных с точки зрения метрологии.