Here is a general review of long-term magnetotelluric (MT) studies of the lithosphere of the Fold Belt of Eurasia (North Caucasus, Altai-Sayan, Koryak-Kamchatka, and Tien Shan regions). The results have contributed to the development of the geological and geophysical database for seismic zoning, identification of active tectonic structures, and exploration of mineral resources. In the course of integrated interpretation of the MT data, regional geoelectric models have been constructed, conductive anomalies have been related to low-velocity and high-absorption zones, deep-seated conductive faults and rheologically weak zones have been identified, and their relationship to the location of earthquake hypocenters and miscellaneous volcanic features has been studied. The research involved 1D, 2D, and 3D MT data inversions. The inversions were preceded by the analysis of the invariants of the impedance tensor. The initial models for solving 3D inverse problems by trial-and-error method or method of formalized inversion of all components (or invariant parameters) of impedance were based on the results of previous 1D and 2D inversions. As a result, a correlation has been found between lithospheric low-resistivity blocks and low-velocity or high-absorption domains in most of the regions. This provides a basis for more reliable identification of weak zones and estimation of water fraction content in a fluid or melt. However, not all crustal conductive blocks and layers are fluid-related. It has been shown that high conductivity of the Lower Paleozoic – Proterozoic gold-bearing formations in the Southern Tien Shan is attributed to the presence of related graphite and sulfide inclusions.

The territory of the Belarusian-Baltic region, located in the west of the East European craton, has been represented by a three-dimensional block model showing a regular decrease in the average consolidated crustal thickness of the blocks from 59 to 39 km, in the average longitudinal wave velocity from 6.80 to 6.50 km/s, and in the lower crustal magnetization from 4–5 to 0.5 A/m. A comparative analysis of the 3D model of the deep lithospheric structure and epicentral distribution of 67 significant local tectonic events of the Belarusian-Baltic region for the period 1602–2008 showed that the Baltic part of this region experienced 6.33 times as much earthquakes and 6.76 times as much total energy release than the Belarusian part of it: 58 earthquakes and the total seismic energy release equal to 1.0399·10¹³ J against 9 events and 1.5382·10¹² J. The vast majority of the earthquake epicenters fall within the different-type crustal block boundary zones, with the maximum number of earthquakes of the Baltic part of the region (27) occurred at the boundaries between the thickest and most solid Incukalns block of the Earth’s crust (average thickness – 59 km. average longitudinal wave velocity – 6.80 km/s) and adjacent thinner and less solid crustal blocks. The earthquake epicenters of the Baltic part of the region are largely concentrated on the Baltic Sea coast. It has been found that during the first three days after the 28.12.1908 Messina 7.1 magnitude earthquake, largest in Europe, the Belarusian-Baltic region was hit by nine significant 3.8416·10¹² J total seismic energy earthquakes, which corresponds to 32 % of the whole seismic energy released therein over a 400 year period. Substantiation has been provided for the initiation of the East Baltic rift system of triple junction, its sufficient plume energy supply, which causes high seismic activity of the Baltic part of the study region. A combination of vertical and horizontal forces acting at the crustal blocks of the Belarusian-Baltic region determines the oblique-slip earthquake focal mechanism in the brittle upper consolidated crust.

The RAS Research Station conducts geodynamic research on the Bishkek geodynamic test area (BGTA) using on-power time-lapse measurements of an unsteady electromagnetic field produced by a grounded electrical line.

In order to relate the electromagnetic monitoring signals to the recorded seismic events, the authors proposed the following characteristics (indicators):

1. a) time of arrival of a maximum value signal at the observation point;
2. b) voltage-time characteristics of the pulse;
3. c) confidence interval for the average daily values of a signal.

The sensitivity of these indicators to seismic events was illustrated by the example of a swarm of seismic events (K>8) recorded near the village of Kegety at the BGTA in April 2017. It has been found that, in the period of April 1–17, 2017, the time series of the three indicators contained no temporally synchronized anomalies. However, on April 18–20, 2017, all indicators showed the distinct temporally synchronized anomalies, which can be considered as precursors of the Kegety earthquake swarm whose main shock was recorded on April 21, 2017.

The paper substantiates the possibility of using the above-mentioned indicators for medium-term prediction of seismic events. In order to automate the processing of the time series, it is proposed to create a digital platform to analyze a long-term array of electromagnetic monitoring data from all observation points.

This paper starts a series of publications on the diffusion kinematics of non-stationary sounding in relation to the problems of electromagnetic monitoring of seismotectonic processes.

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.

When studying the relationship between electromagnetic and deformation processes, according to the results of magnetotelluric monitoring, electromagnetic pulses were detected, which may be associated with the earthquakes that occurred. The observations were carried out at two magnetotelluric stationary monitoring points located in the Chu depression (Aksu 42.60911 °N, 74.00833 °E; Chon-Kurchak 42.62828 °N, 74.60671 °E, Northern Tien Shan), on the territory of the Bishkek geodynamic polygon. To identify earthquake responses, the results of instrumental observations of the electromagnetic effects of a strong earthquake and its aftershocks that occurred in northern China on January 22, 2024 with a magnitude in the range of 4.9–6.9, a weaker one with a magnitude of 5.4 (Kyrgyzstan) and a number of powerful remote earthquakes with a magnitude in the range of 5.2–6.6 at a distance of 500–1200 km from the epicenter were analyzed. It is shown that an earthquake with numerous aftershocks located at distances from ~450 km from the registration points is reflected in all recorded parameters, while a weaker earthquake, but located closer, does not manifest itself in one of the horizontal components of the electromagnetic field. The mechanisms of occurrence of seismoelectric signals and mechanical-electromagnetic transformations in the Earth’s crust are considered. The reality of the appearance of electromagnetic precursors of earthquakes and coseismic signals observed in the first tens of seconds or minutes after an earthquake is shown. The results of the research can be used in the development of methods for monitoring seismic activity in potentially dangerous regions.

The article considers the methodology of obtaining geoelectric characteristics of the medium for the experimental electrical exploration complex with pseudonoise signals intended for studying modern geodynamic processes occurring in the lithosphere of the Northern Tien Shan, taking into account the features of its hardware and software implementation. The influence of instability of the amplitude of probing current pulses on the transient curve is considered when the probing setup is powered by batteries. A technique is proposed for accounting for changes in current in the probing frame, which allows for additional improvement of the signal-to-noise ratio in the obtained probing curves. Based on the works of V.A. Sidorov and M.S. Zhdanov, variants of an approximate solution to the inverse problem of Transient Electromagnetics Method (TEM) are shown, implemented in the software of the electrical exploration complex. A technique for improving the method for solving the inverse problem of TEM within the framework of a model with a conducting S plane is considered, which allows for increasing the reliability of the results.

This article provides examples of aftershock sequences in the context of time series of the geomagnetic field variations ΔТ for the 2003–2007 period when the Bishkek geodynamic polygon area experienced an increase in seismic activity. These examples are supplemented with an analysis of a series of the 2017 Kegety earthquakes accompanied by a large number of aftershocks; besides, an attempt has been made to analyze the impact of the January 22, 2024 Uqturpan earthquake, China, – the last major M7.0 event, – on the geomagnetic situation within the monitoring network. Changes in the stress-strain state of the geoenvironment associated with the generation and occurrence of earthquakes are recorded in the form of abnormal variations of the geomagnetic field due to the use of high-precision magnetovariation stations operating at the observation locations RS RAS. A relationship has been found between the ΔT variations and the impending earthquake by comparing the magnetometric data with the catalog data from the KNET seismological network. The stationary sites monitored ΔТ variations during seismic events with different energy classes K and, if the earthquakes of energy class K=6–8 (weak) are visible on the ΔТ graphs just sometimes against a continuous background, then the events with K≥10, especially those accompanied by a large number of aftershocks, are seen thereon as well-defined ΔТ anomalies. It seems promising to conduct this kind of research for other earthquakes in order to study the influence of seismic events on variations of the geomagnetic field.

The January 23, 2024 М7.0 Wushi earthquake (China) put an end to the period of strong earthquake quiescence that had lasted for about 33 years in the Tien Shan. The risk of occurrence of new strong earthquakes in the coming years has been discussed among scientists. As a result of the conference on the basis of RS RAS in Bishkek in 2024, a team of the Russian, Kyrgyz, Kazakh and Uzbek seismologists, geophysicists and tectonophysicists has been formed to collaborate on a study of seismic prediction in the Tien Shan to reach a new level of understanding of this problem and to obtain the possibility to solve it. In the last few decades, a large Tien Shan earthquake database has been compiled and catalogued involving not only place, time and intensity of an event but also earthquake focal mechanisms. For the last years, M.V. Gzovsky laboratory of tectonophysics, IPE RAS, dealt with the development of new approaches which allow the stresses, extracted from the seismological database, to be recalculated into the Coulomb stresses on active faults. The recalculation experience showed that the fault zones with high Coulomb stresses can also be distinguished as more intensive seismic regime areas. Those are areas along which there is an occurrence of earthquakes, both moderate to strong and catastrophic (retrospective prediction for the 2008 Wenchuan and 2023 Pazarcik earthquakes). Thus, it becomes possible to perform tectonophysical zoning of faults which can be considered as a long-term earthquake prediction. The joint research program also involves a new level of development of approach to moderate-term earthquake prediction as applied to certain faults.

Seismic hazard assessment remains one of the priorities of tectonically active regions. It is based on the data for sesimogenic ruptures indicating the segments of active surface faults. Based on the predecessor data, continuous satellite imagery interpretation, drone aerial photography, GPR profiling and morphostructural analysis, the authors of this paper have obtained new data concerning the location and main parameters of seismogenic ruptures in the Baikal rift. GIS format has been used to map surface ruptures along the Baikal coast with compiling the relevant digital database available on the http://activetectonics.ru website. By a number of features the ruptures are grouped into 20 zones, 6 of which consist of the secondary ruptures in the Khamar-Daban Range. The latter could result from a simultaneous impact of structural (tectonic structure), seismic and climatic factors (glacial retreat and load relief) which presently allows them to be classified as seismogravitational structures. Length-based and maximum single acting displacement-based calculations were made of the maximum possible magnitudes for the primary rupture zones. Seismic potential of the best-studied seismogenic zones of the Baikal rift is М_W=7.2–7.3 and M_S=7.3–7.5. On one hand, the present paper summarizes once again the results of the studies of seismogenic ruptures in the Baikal rift and on the other takes this issue to the next level. The obtained results have important implications for refinement of seismic hazard assessment and development of educational tourism in the region.

The article presents the results of studying the sources of terrigenous material deposition in the Uralian foredeep according to U-Pb dating of detrital zircons from terrigenous rocks of four stratigraphic levels of the Kapysov formation (Sakmarian stage). The Kapysov formation is one of the formations of the Lower Permian section of the Yuryuzano-Sylvenskaya depression in the Uralian foredeep. It is composed of conglomerates and sandstones and unconformably overlies the underlying formations. Samples 14110 and 14110-1 were taken from the same section exposed in the quarry near the village of Tatarsky Maloyaz, from coarse-grained sandstones of the conglomerate matrix in the lower parts of the formation; sample 15004 was taken in the quarry near the town of Mikhailovsk, from gravel sandstones in the middle part of the formation; sample 18228 was taken in the quarry at the southern end of the village of Elgildino, from sandstones of the upper part of the formation. In each sample. there were determined two zircon populations: Precambrian (mostly rounded grains) and Paleozoic (mostly unrounded grains). The relative amount of grains of the Precambrian population decreases gradually up the section from 90.9 to 31.8 %, with a corresponding increase in the amount of Paleozoic zircons. The Precambrian zircon age spectra of all samples are approximately the same, which suggests that they were derived from the same source. This assumption does not contradict the results of the Kolmogorov-Smirnov test (the coefficient varies from 0.316 to 0.999). These spectra are almost identical with the zircon age spectra in the Vendian Asha group of the Bashkir megazone from which the detrital zircon grains could have been derived. This situation suggests a very likely possibility of short-distance transportation since the complexes of the Yuryuzano-Sylvenskaya depression are overlapping directrly with the Bashkir megazone. The age spectra of the Paleozoic deterital zircon grains differ significantly for different levels. The Paleozoic zircon population gradually attains the younger age up the section of the the Kapysov formation: from the Ems to the Middle Carboniferous. Zircon grains with an age of about 400 million years could have been derived by erosion of the ophiolite and island-arc rocks of the Urals whose age is similar to that of the Baymak-Buribai complex. The Carboniferous zircon crystals are the products of the destruction of magmatic complexes in the Magnitogorsk and East Ural megazones.

The combination of newly obtained geological, petrological and geochronological data on the rocks from the Kabak-Taiga ophiolite massif of the Gorny Altai and already published materials on similar characteristics of the ophiolites from Tuva allows us to conclude that an initial back-arc basin at the rear of the Tannuol island arc dates back to the Vendian – Middle Cambrian. Its formation lasted for about 70 million years. The fragments of the back-arc basin are confined to the Middle Paleozoic Charysh-Terekta-Ulagan-Sayan suture-shear zone, formed as a result of the subduction of the oceanic crust of the back-arc basin beneath the Vendian-Cambrian Tannuola island arc of the Paleoasian Ocean.