It is proposed in this paper to use the focal characteristics of small seismic events, in particular, the scaled energy and the rupture propagation velocity, as indicators of possible dynamic movements along a fault. The two sites selected for analysis underwent microseismic events induced by mining operations. The first site, the Korobkovskoe iron ore deposit of the Kursk Magnetic Anomaly, is located in the aseismic region. The second site, the apatite–nepheline deposit of the Khibiny massif, is characterized by relatively intensive natural and human-triggered seismicity. Based on the results of the analysis, the values of the scaled seismic energy and the rupture propagation velocity are drastically different at the deposits under consideration. At the apatite–nepheline ore deposit, the parameter values are close to the range of values characteristic for “normal” earthquakes. At the KMA deposit, the obtained anomalously low values of the scaled energy and the rupture propagation velocity correspond to “slow” earthquakes. The results obtained are indicative of the prospects for using the selected parameters as indicators of possible large dynamic events at the studied site of the fault zone.

Abstract—The disturbances of the geomagnetic field in the surface atmosphere were considered during a series of strong earthquakes that occurred on April 2–3, 2024, in the vicinity of the island of Taiwan. The data from the Mikhnevo Geophysical Observatory of the Sadovskii Institute of Geosphere Dynamics, Russian Academy of Sciences, and the observatories of the international INTERMAGNET network were analyzed. It was shown that in the absence of sole-related global disturbances of the Earth’s magnetic field, earthquakes were accompanied by geomagnetic variations with a maximum amplitude of 10 nT and a total duration of about four hours. The delay time of the magnetic effect relative to the main shock of the first earthquake was 60 min. The ionospheric effect of the event considered was established in the form of variations in the critical frequency of the F2 layer of the ionosphere on the basis the ionograms of height–frequency sounding obtained at the Okinawa ionospheric monitoring station and freely available on the website of the Japanese National Institute of Information and Communication Technologies.

— The geophysical effects of a strong seismic event as two earthquakes with magnitudes of 6.8 and 4.9 occurred on September 8, 2023, in Morocco at close times 22:11 and 22:30 UTC with an epicentral distance between the foci of ~4 km were considered. The data of a number of INTERMAGNET observatories and the magnetic recording results obtained at the Mikhnevo Geophysical Observatory of Sadovsky Institute of Geosphere Dynamics of Russian Academy of Sciences, were used. In the absence of considerable global disturbances of the Earth’s magnetic field, earthquakes were accompanied by a series of three positive bay-shaped geomagnetic variations with a maximum amplitude from ~1 to ~10 nT, following each other after ~60 min. The maxima of the induced magnetic field variations were observed almost synchronously at a distance from ~800 to ~10000 km. The magnetic effect delay time relative to the main shock of the first earthquake was ~70 min. Taking into account the almost planetary nature and high synchronicity of the magnetic field disturbances caused over a significant range of distances, as well as the time delays corresponding in order of magnitude to the travel time of the seismic signal of a distance multiple of the Earth’s dimension, it is suggested that the magnetic effect of the seismic event in question was caused by a global source such as an excited geodynamo. The ionospheric effect of the seismic event under consideration is reported as variations in the critical frequency f 0 F 2 calculated from the data obtained by the ground-based sounding station of the del Ebre Observatory.

The variations of the Earth’s magnetic field in the period 2013−2023 are considered on the basis of data from the INTERMAGNET network observatories located in the South Pacific Ocean. It was shown that El Niño in 2015 was accompanied by anomalous geomagnetic variations with an amplitude of up to 120 nT with a well-manifested increase in their mean-square deviation by 1.5 times relative to the average values of 2013. For the period from the end of 2022 to the beginning of 2023, a dramatical increase in the variations of the geomagnetic field and an increase in their mean-square deviation by 2.5 times relative to 2021 was recorded. This fact may indicate the beginning of the activation of a strong El Niño, the maximum intensity of which should be expected in 2024.

An analysis of variations in the microbaric background and the terrestrial magnetic and electric fields in the surface layer of the atmosphere accompanying strong earthquakes that occurred on February 6, 2023, in Turkey, is presented. The analysis involved the results of instrumental observations performed at the Moscow Center for Geophysical Monitoring and the Mikhnevo Observatory (Institute of Geospheric Dynamics, Russian Academy of Sciences), as well as the data obtained by a number of magnetic observatories of the INTERMAGNET network. It is shown that, in addition to the seismic effect, these earthquakes were accompanied by variations in the magnetic and electric fields, as well as by the generation of infrasonic waves recorded at a considerable distance from the sources.

Deep velocity models of the lithosphere of the Khoper Block and Losevskaya Suture Zone of the Voronezh crystalline massif of the Sarmatia Protocraton are obtained for the first time by the receiver function technique. The crust is determined by a four-layered structure with a waveguide in the lower part of the section. The presence of a zone of lower velocities in the upper mantle at depths of 110–150 km, which mark the mid-lithospheric discontinuity (MLD), as well as their characteristics, is identified for the first time for the Khoper Block. A complex, probably, gradient structure of the crustal–mantle transition is determined.

For the first time, based on the receiver function technique, lithospheric velocity models of the Khoper block and the Losevskaya suture zone was obtained. Mentioned structures belongs to the Voronezh crystalline massif of the Sarmatia protocraton. The crust is defined by a four-layer structure with the presence of a waveguide in the lower crust. For the Khoper block of Sarmatia, the presence and characteristics of low velocity zone in the upper mantle at depths of 110–150 km, marking mid-lithospheric discontinuity (MLD), have been identified and determined. A complex, possibly gradient, structure of the crust-mantle transition has been revealed.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070103

The results of instrumental observations of acoustic oscillations and geomagnetic variations during the fall of the bolide on 04/19/2023 in the area of Kiev (Ukraine) are presented. It is shown that the explosion of the car was accompanied by an acoustic signal recorded at a considerable distance from the epicenter of the event (~755 km), and manifested itself in variations of the magnetic field. According to acoustic observations, 4 explosions of the largest fragments of the car were recorded. The total energy of the event was 4.2–1011 J, which corresponds to about 0.1 kt in TNT equivalent. The maximum amplitude of geomagnetic variations caused by the explosion of the bolide at distances in the range of 454–909 km was from 2.5 to 4 Nt.

The global nature of the induced geomagnetic variations was demonstrated using the magnetic observation data obtained at the INTERMAGNET network observatories during the period of the double earthquake on March 16, 2022 (Japan). Their synchronism and comparable amplitude over a wide range of distances from 210 to 10 000 km, the delay time relative to the considered seismic events ( 55 min), and the predominant period of variations of 30 min are indicative of the fact that the source is a geodynamo perturbed by the action of seismic waves propagating deep into the Earth.

The results of instrumental observations of acoustic oscillations and geomagnetic variations during the bolide-fall event on April 19, 2023 in the region of Kyiv (Ukraine) are presented. It is shown that the bolide explosion was accompanied by an acoustic signal recorded at a great distance from the epicenter of the event (~755 km) and was manifested in variations in the magnetic field. According to acoustic observations, four explosions of the largest fragments of the bolide were recorded. The total energy of the event was 4.2 × 10 11 J, which corresponds to about 0.1 kt in trinitrotoluene (TNT) equivalent. The maximum amplitude of geomagnetic variations caused by the bolide explosion at distances in the range of 454–909 km was 2.5 to 4 nT.

We present the data of instrumental observations made at the Mikhnevo geophysical observatory of the IDG RAS of magnetic field variations and the response of microbaric oscillations and the electric field in the Earth’s surface atmosphere to a strong magnetic storm on April 23, 2023 (Kp = 8). When determining the response of the ionosphere to a magnetic disturbance in the form of a change in the critical frequency of the F2 layer, we use the results of ionospheric sounding performed at the IAP (Leibniz-Institut Fur Atmospharen Physik). It is shown that during periods of maximum magnetic field variations, increased microbaric variations are recorded and increased electric field variations are noted. The magnetic storm was also accompanied by a change in the critical frequency f0F2, as well as in the spectral characteristics of variations in the electric field strength.

The results of instrumental observations carried out at observatories of the INTERMAGNET network and at the Wakkanai ionospheric sounding station were used to show that the vigorous effusion–explosion eruption of Shiveluch Volcano occurring on April 10, 2023 was accompanied by variations in the Earth’s magnetic field, as well as by changes in the critical frequency of the ionospheric F 2 layer.

The magnetic effects of strong earthquakes are considered using the example of a unique event: two underwater earthquakes of magnitude 6.0 and 7.3 that occurred on March 16, 2022 at close times (at 14:34 and 14:36 UTC, respectively) with a distance between sources of ~11 km. With the use of data from the Mikhnevo geophysical observatory of the IDG RAS (MHV) and a number of magnetic observatories of the INTERMAGNET international network, it is shown that in the absence of global geomagnetic disturbances, earthquakes were accompanied by characteristic variations of the Earth’s magnetic field recorded as a train of alternating geomagnetic field oscillations with an amplitude of ~2–8 nT and a period of ~30 min almost simultaneously at ~15:30 UTC by all magnetic observatories located at distances from 210 to ~13 000 km, as well as by variations in the periods of passage of the seismic and infrasonic signal in the MHV.

New models of the deep velocity structure of the crust and upper mantle are presented for the Khibiny–Lovozero tectonic cluster located in the Kola Peninsula. The artifacts of plume-lithospheric interactions, which evolved in the region from the Proterozoic to the Paleozoic, are discussed. The velocity structure of the Imandra–Varzuga rift structure, the Khibiny and Lovozero intrusions, and the adjacent Archean part of the Fennoscandian Shield is compared in detail. A significant discontinuity of the crustal and upper mantle structure, as well as the structure and the depth of the crustal–mantle transition, is shown. The presence of a zone of lower seismic velocities in the upper mantle related to the mid-lithospheric discontinuity is revealed. The peculiarities of the structure of the Moho discontinuity and the upper mantle in the area of the Khibiny and Lovozero intrusions are interpreted for the first time as artifacts of the plume process.

An analysis of variations in the microbaric background, magnetic and electric fields in the surface layer of the atmosphere, accompanying strong earthquakes on February 6, 2023 in Turkey, is presented. The analysis involved the results of instrumental observations performed at the Center for Geophysical Monitoring of Moscow and the Mikhnevo observatory of the IDG RAS, as well as data obtained by a number of magnetic observatories of the INTERNAGNET network. It is shown that, in addition to the seismic effect, earthquakes were accompanied by variations in the magnetic and electric fields, as well as the generation of infrasonic waves recorded at a considerable distance from the sources.

The paper presents new deep velocity of the earth’s crust and upper mantle in the Khibiny-Lovozero tectonic region located on the Kola Peninsula. The artifacts of plume-lithospheric interactions that occurred in the investigated area from the Proterozoic to the Paleozoic time are discussed. A detailed comparison of the velocity structure of the Imandra-Varzug rift, the Khibiny and Lovozero plutons, and the adjacent Archean part of the Fennoscandinavian Shield has been carried out. A significant heterogeneity of the structure of the crust, upper mantle, as well as the structure and depth of the crust-mantle transition is shown. The presence of a zone of low seismic velocities in the upper mantle associated with the mid-lithospheric discontinuity (MLD) has been revealed. Structural features of the Moho zone and the upper mantle in the region of the Khibiny and Lovozero plutons were interpreted as artifacts of the plume process.

—During a series of destructive earthquakes in Turkey on February 6, 2023, in particular, two strong earthquakes with magnitudes 7.8 and 6.7 immediately following each other, the results of instrumental observations of microbaric and geomagnetic variations made in the surface layer of the atmosphere, as well as variations of the electric field and the critical frequency of the regular F 2 layer of the ionosphere are presented. It is shown that the earthquakes were accompanied by variations of magnetic and electric fields, generation of infrasound waves recorded at a considerable distance from the sources, as well as variations of the critical frequency f 0 F 2.

A numerical model of the influence of a strong earthquake on disturbances to the geomagnetic field is proposed. The impact on the epicentral region of the Earth’s ionosphere of wave atmospheric disturbances caused by a seismic event is considered as the main mechanism of the magnetic effect. The estimates made on the basis of the proposed model using the example of a strong earthquake on March 11, 2011 (Japan, M = 9.1), are consistent with the results of instrumental observations.

На основе анализа результатов инструментальных наблюдений показано, что эксплозия вулкана вызвала серию волновых возмущений в атмосфере, а также вариации электрического и магнитного поля Земли на значительных эпицентральных расстояниях. Атмосферные возмущения зарегистрированы в виде волн Лэмба с источником в эпицентре эксплозии, а также виртуальным источником, расположенном в антиподе, и формирование которого связано со схождением и суммированием сигналов, распространяющихся вдоль земной сферы. Помимо первичных волн зарегистрированы вторичные и третичные волны, сформировавшиеся в результате неоднократного прохождения вызванного эксплозией сигнала вокруг земной сферы. Выполнена оценка энергии источника.