Analysis of seismicity in Kamchatka and Japan demonstrates that, within the framework of nonlinear dynamical systems, it is possible to estimate the key parameters of a system of equations acting as a “generator” of the seismic regime. Based on the introduced seismic parameter, estimates are obtained for the embedding dimension and the fractal dimension of the phase portrait for the dynamic seismicity system. The former indicates the dimension (the required number of equations) of the dynamical system needed to describe the seismic regime, whereas the latter reflects the degree of chaos (randomness) in the system’s solution. This analysis spans a wide range of energy, spatial, and temporal scales. A distinct shift in the properties of such a system generating the dynamics of seismicity is observed in association with the Tohoku megaearthquake.
The evolution of tectonic faults and localization of strong earthquake sources are controlled by the configuration and rheological properties of tectonic asperities. Seismogenic spots are a seismic manifestation of tectonic asperities and can be identified on the basis of spatiotemporal analysis of seismicity, namely, they represent topologically dense spatial groups of background seismicity. This study investigates the seismicity patterns of the Kamchatka Subduction Zone (KSZ), where the oceanic Pacific Plate subducts beneath the continental Okhotsk Plate along the Kamchatka Peninsula. We used the regional seismic catalog from the Kamchatka Branch, Geophysical Survey, Russian Academy of Sciences, which includes 38 886 events recorded from January 1, 1990, to September 14, 2025. The magnitude of completeness (Mc) for the catalog is 3.0. Seven seismogenic spots, with characteristic sizes ranging from 150 to 250 km, are identified within the KSZ. The structuring of these spots is shown to persist throughout the entire 35-year observation period. The boundaries of the seismogenic spots are consistent with the structural features of the subducting Pacific plate. Within these seismogenic spots, 18 out of 23 epicenters of earthquakes with magnitudes greater than 7 that have occurred in the region since 1900 are localized. The source structure of the strongest Kamchatka megaearthquake Mw 8.8 on July 29, 2025, which reflects the configuration of tectonic asperities, is in full agreement with the configuration of the KSZ seismogenic spots.
The article analyzes volcanic swarms during periods of magma intrusion at Redoubt and Augustine volcanoes from the perspective of seismic regime. It is shown that the two volcanic swarms observed prior to the 2009 eruption of Redoubt Volcano differ in both their temporal energy release patterns and their frequency-magnitude distribution (b-value). Furthermore, the second swarm, occurring immediately before the eruption, features a more prominent strongest event, with the majority of other strong events clustering within a few hours prior to it (considering the swarm’s total duration of approximately three days). Abruptly following the strongest event, the seismic energy release drops sharply, which deviates from the classical pattern of swarm activity. The number of events and their maximum magnitudes showed a gradual increase from the swarm’s onset toward the strongest event. Furthermore, a decrease in the b-value was observed prior to the strongest event, compared to the elevated values recorded at the beginning of the swarm. These patterns are also identified during the intrusion period preceding the 2006 eruption of Augustine Volcano, though over a longer temporal scale. Such behavior is successfully explained within the framework of rock failure and magma intrusion models.
Using ground-based magnetometer stations and vertical ionospheric sounding stations, we investigate the intensification of variations in the geomagnetic field and ionospheric electron density associated with the July 29, 2025 strong megathrust Kamchatka earthquake and its aftershocks over a thousand km from the observation stations. The recorded anomalous geomagnetic and electron density variations are interpreted as resulting from the propagation of three types of earthquake-induced waves: seismic Rayleigh waves, atmospheric internal waves originated at the earthquake epicenter, and slow magnetohydrodynamic waves generated via the transformation of atmospheric waves in the lower ionosphere.
Paleomagnetic studies were performed on red-colored siltstones from the lower part of the Early Ediacaran Kumakh-Ulakh Formation (western slope of the Aldan Shield, southern Siberian Platform), representing a postglacial sequence associated with the Marinoan glaciation (645–635 Ma). Under the Geocentric Axial Dipole (GAD) model, the obtained results indicate a near-equatorial position of the Siberian Platform during the deposition of the Kumakh-Ulakh Formation, which supports the Snowball Earth hypothesis. On the other hand, the distribution pattern of the Kumakh-Ulakh Formation virtual geomagnetic poles may indicate the contribution of an equatorial-dipole component to the Early Ediacaran geomagnetic field, thus deviating from the actualistic GAD model. In this case, the result cannot be used to support the Snowball Earth hypothesis. Regardless of the geomagnetic field configuration during the time period under consideration, the obtained paleomagnetic data suggest that the post-Marinoan deglaciation processes were not associated with a significant change in the latitudinal position of the Siberian Platform. This conclusion, however, is based on the assumption of a constant contribution of the axial and equatorial dipole components to the main geomagnetic field during the Late Cryogenian and Early Ediacaran.
The article presents the results of electromagnetic soundings performed at the carbon test site Seven Larches in the Yamalo-Nenets Autonomous Okrug. The surveys were carried out using the controlled source radiomagnetotelluric (CSRMT) and the transient electromagnetic (TEM) methods. The CSRMT surveys were performed in scalar mode within the 0.5–1000 kHz frequency range, measuring signals at three fundamental frequencies (0.5, 5, and 50 kHz) and their odd subharmonics. TEM measurements were conducted using a 50 × 50 m single-loop setup. The TEM curves showed transient processes with a double sign reversal of the signal, indicating the influence of frequency dispersion of resistivity. Joint interpretation of the CSRMT and TEM data allowed us to estimate the frequency dispersion parameters and take it into account during TEM data inversion. Numerical modeling showed that the effect of frequency dispersion on the CSRMT sounding results was insignificant under the given conditions. Some influence of static shifts on the CSRMT curves was corrected by spatial data filtering. Based on the electromagnetic sounding results, resistivity sections along two profiles were obtained. The sounding data are consistent with available geological and cryological information for the study area. The structure of the section can generally be characterized as horizontally layered. The upper part of the section, down to a depth of 20 m, is heterogeneous in electrical properties, according to CSRMT data. The resulting resistivity section correlates reasonably well with drilling results, which indicate that sedimentary deposits are partially frozen and partially thawed. According to CSRMT data, the top of a high-resistivity layer was identified at a depth interval of 60–80 m, and the TEM data revealed the base of this layer at a depth of approximately 200 m. The layer possibly represents a relict Pleistocene permafrost formation.
Two approaches to solving inverse problems of potential fields using the measurements of the field components and their gradients are considered. Both approaches find the sources of the fields on some two-dimensional varieties. This reduces inverse problems to a two-dimensional formulation, ensuring uniqueness of the solution in a number of cases and accelerating computational procedures. By solving such problems for manifolds located at varying depths, valuable input for geophysical interpretation can be obtained. The proposed methods are suitable for both separate and joint inversion of gravity and magnetic fields. Both approaches guarantee the uniqueness of the obtained solutions and their stability with respect to data perturbations. The first approach to the inverse problems is based on the variational scheme of S-approximation and is implemented using the method of Lagrange multipliers. It allows for localization of sources on several manifolds of different nature. Using field gradient data, this approach can recover not only the sources but also the complex spectra of the fields themselves on one or multiple manifolds. The method is applicable to the processing of local geophysical data as well as for regional and global-scale analyses. The second approach is based on replacing the original inverse problem matrix (which may be ill-posed or even unique) with a nearby matrix, close in norm, that possesses a better condition number. This significantly improves the stability of the resulting approximate solutions, often by several factors. An algorithm, termed the MPMI algorithm (Minimum pseudoinverse matrix with improved condition number), is proposed for the numerical implementation of this approach. The methods for solving inverse problems of potential fields presented in this paper are applied to the processing of real, heterogeneous geophysical data.
This paper presents the results of displacement monitoring over a vast area of the Crimean Peninsula for the period from 2020 to 2024, based on images from satellites equipped with a synthetic aperture radar (SAR). The displacement fields were analyzed and interpreted at both regional and local scales. It was found that 99
We consider the influence of different methods and crustal velocity models on the focal mechanisms of strong earthquakes (Mw ≥ 4.9) in the Southern Baikal Region in 2020–2023. For each seismic event, source parameters were estimated using three approaches: from P-wave first-motion polarities (FM method), by inverting waveforms from regional broadband seismic stations (ISOLA method), and from the joint inversion of surface wave amplitude spectra, recorded at remote broadband stations, and P-wave first-motion polarities (SWP method). Depending on the location of the earthquake epicenter, its source parameters were estimated using a corresponding set of crustal velocity models. In total, seven velocity models obtained by different authors were considered. The results showed that, within a single method, different crustal velocity models do not significantly affect the stability of the focal mechanism solutions (the Kagan angle Ф, an angle in 3D space between two focal mechanisms, is generally less than 10°). This is because the wavefield recorded at regional (∆ > 100 km) and teleseismic distances, with wavelengths significantly exceeding the rupture length, is not sensitive to the details of the velocity structure of the geological medium. When comparing solutions obtained by different methods, a slight variation in the estimated parameters is also observed (most Ф-values are less than 30°). Thus, the example of strong earthquakes in the Southern Baikal Region (Mw ≥ 4.9, 2020–2023) demonstrates that robust estimates of source parameters can be obtained using simplified crustal velocity models. This study also confirms the potential of tensor solutions based on the joint use of teleseismic and regional data. In this case, the hypocentral depth and energy characteristics are determined along with the focal mechanism solution.
Geomagnetic field models and their-derived models of near-surface currents in the Earth’s core (i.e., at the core-mantle boundary) exhibit structural features that correspond to periodic zonal flows. Taking into account that Rossby waves and large-scale circulation may exist near the core–mantle boundary, their interaction is analytically examined. It is shown that this interaction results in instability, driving the emergence of zonal flows and the formation of their quasi-periodic structure in the meridional direction.
An approximate analytical solution to the direct problem of microseismic sounding is presented, based on the theory of surface acoustic wave propagation in plane-layered media and relies on the assumption of energy flux conservation. In the two-dimensional delivery, a plan-layered medium with local inclusion is considered. To be able to obtain a solution, parameterization of the medium model is necessary; therefore, several variants of this procedure have been proposed and analyzed. Since the proposed approach does not directly take into account the reduction in a wave’s absolute horizontal resolution, a variant of additional processing of the resulting solutions was developed, tested on a simple model of two buried rods. A comparison with the numerical solution for the initial heterogeneity model showed that the discrepancy between the analytical and numerical results with a sufficiently large degree of parameterization is about 5
The generation of secondary microseisms occurs most efficiently in situations when two wave systems propagating in opposite directions are present on the sea surface. The main factors that lead to a reduction in the energy of surface waves transferred to the Earth’s crust are: the different ratio of wave heights between the first and second systems, the different frequencies of their spectral peaks, the deviation of propagation directions from the opposing one, and the width of the angular distribution function of wave energy. Dependences describing the changes in transferred energy with respect to these factors have been constructed. It has been shown that only a small fraction of the energy of ocean waves is transferred to the Earth’s crust during the generation of secondary microseisms.
We present the results of examining the variability in the estimates of the complex parameter of seismicity RTL and the b-value of the Gutenberg–Richter frequency–magnitude relationship. Both parameters are frequently used in practical applications such as anomaly detection and earthquake forecasting. The calculation of these parameters involves a number of adjustable algorithm settings and alternative statistical estimation methods. The choice of a specific settings can be crucial to the calculation results, potentially reflecting algorithmic artifacts. In this paper, we explore the stability of these seismicity parameters with respect to the tuning coefficients in corresponding algorithms, using earthquake catalogs from Northern California and Kamchatka. Our results show that the empirical coefficients of the RTL algorithm have a characteristic effect on the calculation results: beyond certain threshold coefficient values, the variability of the results becomes negligible. A similar effect is observed when varying the spatial window for both the RTL and b-value calculations. We estimate the scatter of the results calculated under varying algorithm settings and analyze how this scatter varies across several distinct spatiotemporal regions within seismically active regions.
The article presents the results of remote determination of the rock saturation type and estimation of the total thickness of productive intervals based on recordings of natural seismic background noise. Field data were processed using both methods previously proposed by the authors and new ones. These methods are based on the well-known empirical phenomenon—the appearance of a positive spectral anomaly in the seismic background above a hydrocarbon deposit in the 1–10 Hz frequency range. The field data recorded near wells and along the profile in mature fields in the desert of southeastern Kuwait were analyzed. The developed methods were found to be equally effective for analyzing hydrocarbon deposits with both carbonate and terrigenous reservoirs at different stages of development. Empirical mode decomposition allowed for the separation of the oscillating and trend components of the productive interval thickness estimates, which characterize different geological and geophysical features of the study area. The maxima of the trend component mark the position of large oil-bearing geological blocks, while the minima correspond to inter-block boundaries with no oil content. The oscillating modes reflect local features of the degree of rock oil saturation. The proposed methods and techniques are valuable tools in oil and gas exploration for constructing maps of total productive interval thickness and selecting the most promising drilling locations. They can also be applied in the development of mature fields to identify water breakthrough zones, delineate water-flushed compartments, and locate poorly drained, oil-filled areas. The new acoustic method for detecting water saturation of rocks is promising for developing technologies to prospect for underground high-quality drinking water sources in arid and industrial regions, which is an urgent modern problem.
A global systematic analysis of seismic moment tensors of tectonic earthquakes was conducted using the GCMT catalog period from 1976 to 2025. To identify earthquakes with sources inconsistent with the double-couple model (NDC earthquakes), we applied a method that estimates the angle between the slip vector and the rupture plane based on the principal values of the seismic moment tensor while accounting for their uncertainties. Out of 68е540 analyzed earthquakes with Mw ≥ 4.5, 3.4
Comparison of several effective medium theory methods was performed to describe the degradation of the elastic moduli of red sylvinite samples subjected to cyclic uniaxial compression with an increase in maximum load after each cycle. The predicted values of the Young’s modulus of red sylvinite after each loading cycle were determined using X-ray computed microtomography (CT data). The dependence of the deformation characteristics of red sylvinite on the maximum load in a cycle was experimentally determined. At loads up to 10 MPa, the tangent modulus of deformation changes insignificantly (≤10
The natural seismicity of the Republic of Karelia is studied for the period from 2000 to 2024. The presented results are confirmed by data from the Karelian seismic network and seismic stations in neighboring regions. The geological structure of the study area, characteristics of seismic equipment, programs and data processing methods are briefly described. The presence of a seismic network in the region makes it possibble to calculate the main parameters of events and determine their characteristic features. During the specified period, 80 earthquakes with magnitudes from 0.5 to 3.2 were detected, and the data were included in the consolidated seismic catalog of Karelia. Even weak tectonic earthquakes on platforms pose a risk to residential and industrial facilities. Earthquakes mainly occur in the crust at a depth of up to 20 km. The maximum recorded depth of events for the period under consideration is 34 km. The analysis of waveforms and amplitude spectra of local earthquakes was carried out. Seismic events of natural origin are recorded at frequencies in the range from 2 to 18 Hz. The period from 2000 to 2024 is characterized by weak earthquakes occurring in the northern part of the Karelian craton and Belomorian mobile belt. The number of instrumentally recorded earthquakes decreases from west to east, with their epicenters located along the main faults and on the lines of the latest ruptures. The obtained results confirm the existence of previously identified zones of local seismic deformations in Karelia—the Belomorian, Paanajarvi and Kalevalsky seismogenic structures.
The time-domain electromagnetic (TDEM) sounding method is effectively used in shallow marine waters all over the world, including the Arctic shelf, where the main object of study is the permafrost layer. A generalized geoelectric model of the Arctic shelf section is presented, which is based on the results of studies conducted by the authors, using archival information from available sources, and contains three main layers: unfrozen bottom sedimentary layer, permafrost layer and subpermafrost layer. Algorithms for solving direct and inverse problems of TDEM are briefly described, including those using the polarization properties of the layers. Typical curves of apparent electrical resistance of TDEM (TDEM curves) are constructed, corresponding to geoelectric models of Arctic waters for three zones: the open sea, the transition zone, and the river mouth. The curves qualitatively reflect the dependence of resistance on depth, except for the case of the most highly resistive section containing a polarizing layer, when the curve is strongly distorted. A series of model experiments were carried out to solve the inverse problem within the framework of a five-layer model. It was shown that when obtaining possible equivalent models that differ from the true one (created by the authors using known parameters), their number can be reduced by fixing the parameters of the water layer, thereby improving the modeling results. The effects associated with the polarizability of the subpermafrost layer, which significantly complicate interpretation, but quickly fade with an increase in the thickness of the seawater layer, were analyzed.
Despite its complex tectonic framework, intense seismicity, and hydrocarbon potential, the Arunachal Himalayan foreland remains poorly characterised by geophysical investigations. This study presents results from a three-dimensional inversion of magnetotelluric data acquired along a profile across its westernmost sector, resolving a pronounced layered resistivity structure. A conductive sedimentary wedge, interpreted as Siwalik molasse and Quaternary deposits, is similar to 0.5 km thick beneath the Brahmaputra plains and thickens northward to similar to 5.5 km beneath the mapped trace of the Himalayan Frontal Thrust, reaching similar to 6-7 km further north. Beneath it, a similar to 13 km thick resistive crustal layer dips northward and overlies a moderately conductive deeper zone. Constrained by passive-seismic velocity models, this resistivity framework indicates a dry, brittle upper crust above a more conductive layer whose nature requires further clarification. These results provide the first geoelectrical constraints in this segment of the foreland, offering new structural information relevant to regional seismicity and guiding future deep geophysical investigations and exploration efforts.
Space weather is the set of processes occurring in near-Earth space under the influence of solar activity. This review presents the principal components of space weather, the causes of their formation, and their impacts on Earth. One of the most significant space weather factors is geomagnetically induced currents in technological conducting grounded systems, caused by rapid variations of the geomagnetic field. Extended conducting systems such as power transmission lines, pipelines, and railways are particularly vulnerable. This paper presents the main results of analysis of the effects of geomagnetic disturbances on the operation of power systems, main trunk pipelines, and railway automation. The results confirm the necessity of developing adaptive protection measures. For an adequate assessment of the impact of geomagnetic disturbances, it is necessary to further develop short-term and long-term space weather forecasting systems, local models of Earth’s crustal conductivity, and their integration with real network configurations.
