Leonid M. Bogomolov

В работе исследуются вариации вертикальной компоненты электротеллурического поля (ЭТП) до и после землетрясений, произошедших в период 2024-2025 г. Анализировались данные с двух станций, расположенных на юге о. Сахалин в центральной («Южно-Сахалинск») и западной («Колхозное») части. В качестве датчиков напряженности поля использовались заглубленные металлические пластины площадью 0.25 м2. На станции «Колхозное» для измерений также применялись свинцовые электроды цилиндрической формы. Запись вертикального ЭТП в частотном диапазоне до 10 Гц проводилась в квазиреальном режиме времени с января 2024 г по настоящее время. Цель исследования – проверка гипотезы о возможном использовании вариаций вертикальной компоненты ЭТП как одного из предвестников землетрясения. Конкретной задачей данной работы является исследование вариаций вертикальной компоненты ЭТП на двух станциях в южной части о. Сахалин и анализ взаимосвязи с локальной сейсмичностью. По результатам измерений ЭТП установлено наличие периодов с повышенным уровнем напряженности вертикального поля, не связанные с сезонностью. Сейсмические события с магнитудами M≥2, зарегистрированные на юге Сахалина, происходят преимущественно в эти периоды. Полученные результаты могут свидетельствовать, что вариации вертикальной ЭТП отражают локальные изменения сейсмического режима. This study investigates variations of the vertical component of the electrotelluric field (ETF) before and after earthquakes that occurred during 2024-2025. Data from two stations located in the south of Sakhalin Island in the central («Yuzhno-Sakhalinsk») and western («Kolhoznoe») parts were analyzed. Buried metal plates with an area of 0.25 m2 were used as field strength sensors. At the «Kolhoznoe»station, cylindrical lead electrodes were also employed for measurements. Recording of the vertical ETF in the frequency range up to 10 Hz was conducted in quasi-real-time mode from January 2024 to the present. The aim of the study is to test the hypothesis regarding the possible use of variations of the vertical component of the ETF as earthquake precursors. The specific task of this work is to investigate variations of the vertical component of the ETF at two stations in the southern part of Sakhalin Island and to analyze the relationship with local seismicity. Based on the ETF measurements, periods with high levels of vertical field strength, not associated with seasonality, have been identified. Seismic events with magnitudes M≥2, recorded in the south of Sakhalin, occur predominantly during these periods. The obtained results may indicate that variations in the vertical ETF reflect local changes in the seismic regime.

The data bank has been created to address the tensor of the seismic moment of earthquakes that occurred in the Altai-Sayan seismically active region in the period 1978–2025. The scalar seismic moment M0 for these events was already known from the CMT catalog. This paper presents estimates of the following dynamic parameters: source radius r, shear stress drop ∆σ, and reduced seismic energy ePR using a phenomenological approach based on previously obtained regression relationships between the source radius r and the scalar seismic moment M0. Stress drop and reduced seismic energy estimates have been obtained for 69 earthquakes with a magnitude MW 3.5–7.2. Thus, it allows to significantly expand the data bank on these earthquake parameters for the Altai-Sayan seismically active region. Maps have been drawn of the areally averaged estimates of stress drop and reduced seismic energy.

The paper presents the results of shallow-depth electrical sounding carried out in 2021–2022 near the Central Sakhalin fault at the geophysical test site of the IMGG FEB RAS (Petropavlovskoye village, Aniva district). Electrical soundings were carried out using a pulse voltage generator developed at the IMGG FEB RAS. The aim of the experiment was to evaluate the response of the medium in the near-fault zone to the impact of current pulses, the amplitude of which is significantly greater than that for resistivity prospecting or seismoelectric prospecting methods but many times less than that for high-power electrical sounding in Central Asia with the aid of geophysical MHD generators or electric pulse installations. The response of the medium was determined based on the records obtained from the seismic instruments located at the Petropavlovskoye test site – a broadband seismometer CME-6111, molecular-electron hydrophone, – as well as on the records of seismic noise at the "Ozhidayevo" and "Kholmsk" stations of the of the SB FRS GS RAS and on short-period seismometers Zetlab 7152-N and SPV-3K installed near the temporary sites in the test area. The results of processing of the seismoacoustic data obtained by a hydrophone for four experimental stages (13 days of serial sounding using unipolar current pulses) showed an increase in the noise amplitude in the near-surface layer during electrical soundings in the Central Sakhalin fault zone. This may indicate the influence of electrical soundings on the sources of seismoacoustic signals, i.e. on the medium destruction at the electrical impact site. Waveform recordings from all seismometers revealed the changes in seismic noise levels that correlate with the passage of cyclones causing high wind loads and changes in atmospheric pressure. Autumn-spring cyclones, frequent in Sakhalin, occurred at all stages of the experiment, which is why responses to electrical impact in seismic noise could only be recorded by the CME-6111 seismometer, located near the sounding source. This research determined the direction for improving electric current sources, increasing their power for shallow and deep sounding of the earth’s crust.

The values of dynamic parameters (DP) for 110 earthquakes with magnitudes MW = 4.7–7.7 that occurred on Sakhalin in 1978–2024 were obtained. A scalar seismic moment was previously determined for these earthquakes. To estimate the other DP: the radii of the foci, the shear stress drop, and the reduced seismic energy a phenomenological approach was used based on the presence of regression, which links the source radius and the values of the scalar seismic moment for earthquakes within the Sakhalin-Kuril region. The results of the study were summarized in a data table. Distribution maps of the averaged values of these DP across the studied region were constructed. Thus, the amount of data on the stress drop and reduced seismic energy for Sakhalin earthquakes has been significantly increased.

This paper presents the results of a methodical (trial) experiment for conducting in-kind conditions on capturing microseepage hydrocarbon molecules by sorption, which amount is sufficient for the certificate of the presence of oil and gas-bearing formations. The experiment simulating hydrocarbon accumulation in traps with sorbents was organized and conducted at the Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences as a step before the installation of traps in natural conditions near a hydrocarbon deposit. Zeolitized tuffs from the Ogonkovsky site of the Lyutogskoye deposit (Sakhalin Island) with a 50 % zeolite content, as well as the peats were used as sorbents. The sorbents were kept for 5 months in an artificial container containing soil (lofts), seawater, and a small additive of a hydrocarbon mixture. The obtained results confirmed the possibility of detecting low concentrations of hydrocarbons in an environment similar to bottom sediments using traps with a zeolite sorbent. The advantage of this sorbent as an indicator of hydrocarbon microseepage over a deposit compared to a peat sorbent was revealed.

In 2024, the Institute of Marine Geology and Geophysics of the Far Eastern Branch of the Russian Academy of Sciences started continuous measurements of the vertical component of the electrotelluric field (ETF), which were integrated into the previously organized monitoring of the horizontal components of the ETF. The vertical component of the ETF is measured by the potential difference between metal plates located in the ground, one above the other, at a depth of about 2 m. Two systems of plates were installed at the Yuzhno-Sakhalinsk geophysical test site (on the territory of IMGG FEB RAS) and were connected to an analog-to-digital converter (ADC). The aim of the study is to identify and analyze variations in the vertical ETF that may be associated with the geological deformation and variations in seismicity. In the first year of measurements of the vertical component of the ETF, 4 periods with an abnormally high level of field strength were identified compared to the average value for the observation period: maximum by 35 times, minimum by 5 times. In total, these periods occupy about half of the entire registration time; it was during these periods that 80% of all earthquakes in the southern part of Sakhalin Island occurred over 11 months of 2024 (24 events out of 30). For the horizontal components of the ETF, no such significant anomalies were observed as for the vertical one. Obtained results indicate that changes in the vertical component of the ETF may reflect variations in seismic activity in the near field. These changes can presumably be considered a sign of earthquake activity near the measurement point.

The paper summarizes the results of field tectonophysical studies of Sakhalin Island conducted by different researchers at different times. Information about the main characteristics of the stress-strained state of the upper part of the Earth's crust (principal stress axes, stress state type, Lode–Nadai coefficient, bedding planes) was obtained as a result of computations using methods of cataclastic analysis of discontinuous displacements, structural-paragenetic, kinematic, conjugate pairs of faults. The input data for the calculations were the materials of field measurements of fracturing, slickensides and structural patterns. The results obtained in the present and previous works on Sakhalin field tectonophysical research are represented in summary tables that include data on local stress states for 264 observation points. The results are incorporated to GIS, the Isoline GIS software is used for the database management system.

В работе представлены результаты анализа данных электротеллурических потенциалов, полученных в пункте измерений, развернутом в июне 2023 года на территории ИМГиГ ДВО РАН в г. Южно-Сахалинск. Уже в первые месяцы работы были обнаружены серии квазипериодических всплесков (импульсов) в ночное время. Сигналы длительностью 4-5 секунд и с периодом следования 130-150 секунд имеют разную форму, которая является производной от некоего оригинального синусоподобного сигнала. Серии отмечались с 20 июля по 11 сентября 2023 г., а их средняя длительность колеблется в районе 8-9 часов. С 12 сентября 2023 года по 10 февраля 2024 года серии не обнаружены. Максимальная интенсивность сигналов и серий в целом наблюдается в период с 5 по 10 августа. В этот же период (9 августа 2023 года) рядом с точкой измерений (в круге с радиусом 0,25 градуса с центром на полигоне) произошло землетрясение умеренной силы с M = 3,8, причём за весь период наблюдений оно было самым сильным из 2 событий с M > 3, произошедших в данном районе. Перед вторым, более слабым землетрясением, подобных серий совсем не было обнаружено. Появление обнаруженных серий квазипериодических импульсов может быть связано с подготовкой очага землетрясения, однако для подтверждения этой гипотезы потребуются дополнительные наблюдения The work represents the results of analysis of electro-telluric potentials data obtained at the Yuzhno-Sakhalinsk test site (deployed in June 2023on the territory of the IMGG FEB RAS). Unexpectedly, a new kind of signals – series of quasiperiodic spikes (pulses) in night times were found in first few months after start of recording. Signals of 4-5 s length and of 130-150 s repetition period have a various waveform, which is derived from some primary quasi-sinusoidal signal. Such series were recorded from July 20 to September 11, 2023, and their average duration was nearly 8-9 hours. No episodes were found after September 12, up to December 20. The maximal intensity of the signals and the series as a whole was revealed in the period from 5 to 10 August. During this period the moderate earthquake M=3.8 occurred on 9 August, 2003 in the vicinity of measurement point (within a circular zone of 0.25 degrees radius around the test site) It was the strongest event from pair of that occurred in the given zone, the magnitudes were being M = 3.8 (08/09/2023) and M = 3.1 (09/19/2023). No similar series were observed before the second earthquake, being the weaker. Origination of quasiperiodic pulses series could be related to the preparedness of earthquake source – site. However extra surveys are required to proof this hypothesis.

The monograph is based on the textbook by T. K. Zlobin (Yuzhno-Sakhalinsk, Sakhalin State University, 2014), which was refined and supplemented significantly. The book presents modern concepts of geodynamical processes in the Earth’s core and its shells (mantle and crust, hydrosphere and atmosphere), up to the space phenomena, which are relevant to a variety of natural disasters: earthquakes, volcanic eruptions, landslides, avalanches, mudslides, tsunamis, storm surges. Tropical cyclones (typhoons, hurricanes, tornadoes), and falls of celestial objects have been characterized as well. Alongside the description of modern geodynamic processes, information is provided on the history of stars, the Sun and planets, the problem of the emergence of the Earth’s magnetic field, the inversion of magnetic poles, etc. The energy of geodynamic processes and natural disasters, their hierarchy and properties: fractality and quasi-periodicity, possible regime changes (bifurcations) have been considered. The monograph is assigned to geologists, geophysicists, specialists in adjacent fields of science, as well as for students and postgraduates studying modern geodynamic processes and related natural disasters.