Том 55, № 2 (2019)

The group velocity dispersion curves are constructed for Rayleigh and Love waves along the paths intersecting the European continent in the interval of periods from 10 to 100 s from the records of earthquakes and seismic noise. The radial anisotropy of the European upper mantle is estimated based on these data. At first, the average velocity sections of the SV- and SH-waves are calculated along each trace from the Rayleigh and Love wave data, respectively. Based on these sections, the average anisotropy coefficient is determined for each path in four depth intervals (the crust + the three 30-km upper mantle layers). These results are used for identifying the variations in the lateral anisotropy in the studied region with the use of tomographic inversion. This approach makes it possible to exclude the different degrees of smoothness of the lateral variations of the SV- and SH-waves if these variations are determined separately from the Rayleigh and Love waves: in this case, large errors in the anisotropy coefficient are possible due to different sets of the paths. The resolution of the data used for tomography was estimated by a “checkerboard test,” which demonstrated the possibility to resolve structural features with a linear size of 1200 to 1300 km in the central part of the studied area, i.e., approximately 15°–50° in longitude and 40°–65° in latitude. The tomographic inversion of the lateral variations in the anisotropy coefficient shows that in the continental part of the studied region, the anisotropy coefficient at all depths in the upper mantle is zero within the error limits, whereas in the region of the Black and Baltic seas, it is positive and equal to 4–4.5% in the subcrustal mantle at the depths of 34 to 64 km. In the underlying layer in the Baltic Sea region, this parameter is close to zero, whereas beneath the Black Sea Basin it remains positive although it decreases to 2–3%. In the lowermost layer, anisotropy is not observed anywhere in the entire region; however, this can be due to the lack of the data for large periods. Positive anisotropy (\({{V}_{{{\text{SH}}}}} > {{V}_{{{\text{SV}}}}}\)) is typical of the oceanic areas which can testify in favor of the oceanic hypothesis of the origin of the Black Sea basin.

This review describes the specifics of the application of the approximation approach in solving the linear and nonlinear inverse problems of geophysics, geodesy, and geomorphology. Within the paradigm proposed by V.N. Strakhov, almost all the geophysical problems can be reduced to solving systems of linear (and, in some cases, nonlinear) algebraic equations. The method of integral representations is the main one for implementing this approach. The application of various modifications of the method of linear integral representations in the spaces of arbitrary dimension is analyzed. The combined approximations of the topography and geopotential fields make it possible to find the optimal parameters of the method for solving a broad range of inverse problems of geophysics and geomorphology and to most fully use the a priori information about the elevations and the elements of the anomalous fields. The method is described for obtaining the numerical solution of the inverse problem on finding the distributions of the carriers of mass that are equivalent in terms of the external field in both the ordinary, three-dimensional, space, and in the four-dimensional space.

Determination of the focal mechanism and source depth of an earthquake by the direct examination of their probable values on a grid in the parameter space also makes it possible to estimate their resolution. However, a detailed search is time consuming. As an example of a source that requires the use of a detailed grid, we consider a special case of a shallow earthquake whose one nodal plane is subhorizontal. Studying these events from the records of long-period surface waves requires a grid that has a high degree of detail for the angles of the focal mechanism. We discuss the application of the methods of parallel computing for speeding up the calculation of earthquake parameters and present the results of the application of this approach for studying the strongest aftershock of the earthquake in Tohoku.

In the sections of two Permian–Triassic trap intrusions of the Ergalakhsky complex, Norilsk region, we revealed the alternation of the intervals of normal and reversed polarity. The near-contact zones of the intrusions are magnetized reversely, whereas magnetization in the central zones has the normal polarity. We present the arguments showing that this change in the polarity along the intrusions section is not the result of postmagmatic remagnetization or self-reversal of remanence but marks the reversal of the geomagnetic field that occurred during the emplacement of the intrusive bodies. As the Ergalakhsky intrusions represent the oldest intrusive trap complex in the Norilsk region, a highly accurate determination of their age is vitally important for the time correlation of the initial stage of magmatic activity. The paleomagnetic data show that the studied sills intruded directly at the Permian–Triassic boundary, at the very end of the Ivakinsky stage. According to the existing estimates for the durations of the reversals, the cooling of the intrusions could last a few thousand years. In the future, the studied sills of the Ergalakhsky complex can be used as a unique object for studying the structure of the geomagnetic field during the reversals and for reconstructing the thermal history under the cooling of intrusions, as well as a reference for estimating the total duration of trap magmatism.

The archaeomagnetic studies conducted at the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS) have made a significant contribution to the international studies of the main magnetic field of the Earth for the past few thousand years. These studies have yielded extensive data on the intensity of the geomagnetic field in the past 8000 years. Four of the most representative and long time series of the data have been constructed for Eurasia: for the Iberian Peninsula, the Caucasus, Middle Asia, and Siberia. Unique studies of rapid variations of the geomagnetic field intensity (with the characteristic times starting from several tens of years) have been carried out which have no analogues in international research. The analysis of the international data on the ancient geomagnetic field made it possible to obtain a spectrum of the variations of the geomagnetic field intensity in the range from decades to millennia and to determine the characteristics of the variations whose superposition can describe the pattern of the changes of the geomagnetic field intensity. It was established that variations with different characteristic times have differently directed the drift and the “main oscillation” (with a characteristic time of 8000 years) has an eastern drift.

On August 7, 2016, an earthquake with magnitude 4.8 occurred in the vicinity of the city of Mariupol close to the southern boundary of the East European Platform (EEP). The earthquake was accompanied by aftershocks with magnitudes ranging from 2.2 to 3.9 that lasted for five days. This region experiences external influence from the neotectonically active Alpine zone, which is expressed in intraplate deformations, horizontal and vertical movements of the Earth’s surface, and seismicity. The sources of the earthquake and its aftershocks are located within the block bounded by the neotectonically active Maloyanisol, Kalmius, and Primorsky faults. In the axial part of the block, a seismogenic structure is traced by the submeridional Kalchik lineament zone identified by the combined analysis of geological and geophysical data and visual interpretation of the satellite image. This neotectonically active zone accommodates the epicenters of the main event and most of the aftershocks.

The analytical formulas are obtained for the tangential components of an extremely low-frequency electromagnetic field in the Earth–ionosphere plane waveguide excited by a grounded linear horizontal antenna. The behavior of the surface impedance is studied as a function of the electrodynamic characteristics of the waveguide and the distance from the source. It is shown that the surface impedance coincides with the plane wave impedance on the Earth’s surface at distances from the source larger than the skin depth provided that the skin layer is thinner than double the waveguide’s height. The influence of the ionosphere on the amplitude of an extremely low- and lower frequency magnetic field and, thus, on the impedance at the shorter distances than two ionospheric heights is theoretically substantiated. This type of effect was observed in the experiments conducted on the Kola Peninsula, where the low conductivity of the Earth allowed the detection of the effect of the ionosphere on the amplitude of the magnetic field in the low-frequency band.