编号 2 (2023)

The results of calculations of the magnetic field structure in the kinematic approximation are presented, testifying to the consistency of the constructed numerical model with the structure of the flows of a conducting liquid: the instability of the convective process in a rotating spherical shell is reflected in the evolution of the magnetic field, manifesting itself in the pulsation regime of the field. It is shown that the features of the field evolution in the calculations are most clearly pronounced at high latitudes and have analogs in the behavior of the real geomagnetic field.

A new method for analytical description of time-dependent signals of different nature based on local and regional versions of the method of linear integral representations in spaces of different dimensions is proposed. The inverse problem of finding the field sources is reduced to solving ill-conditioned systems of linear algebraic equations with an approximate right-hand side. The results of a mathematical experiment on finding elements of nonstationary gravity and magnetic fields of the Earth are presented.

This paper studies instability of a heavy inclusion in the Earth's upper layers by the linear theory method for small perturbations. The existence of such inclusions with increased density is associated with chemical inhomogeneity or phase transitions. The viscoelasticity of the geomaterial is described by the Maxwell rheological model. Two layouts of the inclusion with increased density are considered. The heavy inclusion in the cold upper elastic layer of the crust does not change its location under small perturbations, i.e., it is stable according to the linear theory. The heavy inclusion which is located in the hot viscous crustal layer underlying the upper cold layer, is unstable (slowly sinking into the underlying viscous mantle layers).

Interpretation of magnetotelluric observations made within the Northwestern Caucasus, by means of one-dimensional, two-dimensional inversion and three-dimensional mathematical modeling programs, has helped build testing and starting geoelectric models that are necessary to test and adapt the program of three-dimensional inversion of the impedance tensor components. The performed three-dimensional inversion of the experimental magnetotelluric data has significantly changed the parameters of conducting blocks within the folded structures of the region, identified at the previous stages of MT data interpretation. In the resulting three-dimensional geoelectric model, the position of low-resistance blocks correlates with: suture zones, deep faults, mud volcanoes, and domains characterized by an increased absorption of transverse and longitudinal seismic waves. The electrical resistivity of the most low-resistance anomalies is explained by the degree of their saturation with the water fraction of the fluid.

The paper presents the results of many years of research on the compilation of a consolidated, refined, unified earthquake catalog for the western sector of the Russian Arctic for the entire instrumental observation period, in particular for the period from 1908 to 2020. The catalog includes data on recent seismicity in areas previously unavailable for detailed seismic monitoring. Based on the results of the study, we were able to more accurately determine the spatial distribution of seismicity in the region and compare the instrumental data with parameters of lineament-domain-focal (LDF, or, alternatively, lineament-domain-source (LDS)) models of the General Seismic Zoning maps (GSZ, from Russian term abbreviated as OSR)—OSR-97 and OSR-2016. In the western sector of the Russian Arctic, the highest seismicity is observed in the continent-ocean transition zone, in the Belyi Island, Novaya Zemlya and Severnaya Zemlya archipelagos. The very shelf of the Barents and Kara Seas is characterized by rare and scattered seismicity. The configuration, the maximum possible magnitudes, and the depths of the seismogenic layers in the LDF models of OSR-97 and OSR-2016 maps are not always consistent with the instrumental data and need a correction. The consolidated refined earthquake catalog can be used as a basis for the further research aimed at seismic hazard assessment of the territory, construction of geodynamic models, and study of the stress-strain state of the Earth’s crust.

The paper presents the results of paleomagnetic, rock magnetic, and cyclostratigraphic studies of continental red beds that compose the Permian-Triassic boundary interval of the Staroe Slukino section in the Vladimir Region, Russia. Based on the directions of the characteristic components of the natural remanent magnetization of the studied rocks in the sampled stratum, the intervals of normal and reverse polarity related to the regional magnetozones r₂RnP, r₃RnP, and N₃P-T were identified. Within the r₃RnP zone, there is an interval of anomalous paleomagnetic directions, which has similar characteristics to those identified earlier in the coeval intervals of the Nedubrovo, Zhukov Ravine, and Okskiy Siyezd sections. Revising the biostratigraphy allows us to assume that the two zones of anomalous paleomagnetic directions in the composite magnetic polarity scale of the upper Permian of the Russian Platform are a reflection of the same epoch of an anomalous geomagnetic field configuration. It is estimated by the cyclostratigraphic method that the studied 16 m interval of the Staroe Slukino section took 900±20 thousand years to accumulate, which limits the duration of the geomagnetic field anomalous state near the Permian-Triassic boundary to ~110 000 years. A new Permian-Triassic (~252 Ma) paleomagnetic pole of the East European Platform is calculated: plat = 36.3°; plong = = 155.0°; dp/dm = 2.8°/4.8°.

The evolution of the domain structure (DS) of cubic submicron- and micron-sized magnetite particles has been studied in detail during “cooling” of specimens from the Curie temperature Т_с to room temperature Т_r followed by their “reheating” to Т_с in order to determine the degree of irreversibility of DS changes during heat treatment and their possible effects on the thermoremanent magnetization (TRM) properties. It is shown that typical magnetic configurations in particles up to 2 μm in size have flower or vortex shapes with one or two vortices. A model of the formation of thermoremanent magnetization (TRM) in submicron-sized pseudo-single-domain particles (PSD) is proposed based on an expansion of Neel’s single-domain thermofluctuation model of TRM acquisition. According to the model, the equality of blocking and deblocking temperatures is retained for submicron PSD grains. Consequently, for this magnetic fraction, the Thellier laws of pTRM additivity and independence must also be valid.

A change in the non-stationary electromagnetic (EM) signal over the conducting polarizable Earth covered by sea water on measuring lines located in the axial and equatorial regions of the source – a pulsed horizontal electric line (HEL) – is considered. When the HEL operates under pulsed conditions, it creates a galvanic and eddy current in the medium. If the medium affected by the HEL is heterogeneous, both influences lead to the separation of bound charges. After attenuating the impact of an artificial source, relaxation (depolarizing) processes of various nature appear in such a medium, manifesting themselves, in particular, in the form of an EM signal. As a result, the transient process recorded by the grounded line after the pulsed effect of the HEL is at least a superposition of three components: the transient electromagnetic (TEM) signals, galvanically induced polarization (GIP) and inductively induced polarization (IIP). As the contribution of the TEM field component to the overall signal decreases, the IP signal is manifested in the transient process by a change in the time response of the decay, to the point where the signal reverses polarity. As shown earlier by numerical simulations for the axial region of the HEL, the manifestation of the IIP signal at late transient process times, for most of the geoelectric conditions on land, is invisible against the GIP manifestation (Ageenkov et al., 2020). These calculations also show that in the axial region, the GIP signal manifests itself in the form of a deceleration of the transient process rate, and the IDP signal – an acceleration of the decay rate, to the point where the signal changes its sign. Field measurements performed by the aquatic differential-normalized method of electrical prospecting (ADNME), which uses axial electrical installations, record transient processes with a change in the time response of the decay: it becomes more delayed or, vice versa, runs faster and may be accompanied by a change in the polarity of the signal. In other words, measured signals of different forms are observed, which are presumably associated with the manifestation of the GIP or IIP signals. The relevance of the publication lies in the need to explain the results of field measurements performed offshore, to understand the relationship between the course of the transient process and the geoelectric conditions existing in the water area. And in general, to describe the formation of the transient response of the medium in the axial and equatorial region of the HEL for the conditions of aquatic geoelectrics. The calculated signal for axial and equatorial electrical installations with several spacings under the conditions of the sea shelf water area is studied when the installation is located on the surface of and inside the water layer, and on the seabed of the water area – on geological formations. For axial installations, calculations are made of the quantities used in the ADNME: the transient process ΔU(t), the finite difference of the transient process Δ²U(t) and the transformant P1(t) – the ratio of Δ²U(t) to ΔU(t). For equatorial installations, the signal ΔU(t). is calculated. The signals of a two-layered model of the medium with polarizable and non-polarizable bases are compared.