No 2 (2019)

ARTICLES
Radial anisotropy in the European upper mantle from surface waves
Yanovskaya T.B., Lyskova E.L., Koroleva T.Y.
Abstract

The group velocity dispersion curves of the Rayleigh and Love waves are constructed 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 from these data. Primarily, along each path, the average velocity sections of the SV- and SH-waves were calculated from the Rayleigh and Love wave data, respectively. Based on these sections, the average anisotropy coefficient was determined for each path in four depth intervals (the crust + three 30-km upper mantle layers). These results were used for identifying variations in lateral anisotropy in the studied region based on tomographic inversion. This approach eliminates different degree of smoothness of lateral variations of the SV- and SH-waves when these variations are determined separately from the Rayleigh and Love waves: in this case, the anisotropy coefficient can have large errors due to the 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 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 coefficient is close to zero, whereas beneath the Black Sea Basin it remains positive albeit 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 the large periods. Positive anisotropy (VSH > VSV) is typical of the oceanic areas, which can testify in favor of the oceanic hypothesis of the origin of the Black Sea basin.

Физика Земли. 2019;(2):3-14
views
Gravitational differentiation in the regimes from stokes settling to Rayleigh–Raylor flows
Trubitsyn V.P.
Abstract

The Earth’s core was formed under gravitational differentiation in the course of the separation of iron and silicates. Most of the iron has gone into the core as early as when the Earth was growing. However, iron continued to precipitate even during the subsequent partial solidification which developed from the bottom upwards. At the different stages and in the different layers of the mantle, iron was deposited in different regimes. In this paper, the mechanisms of the deposition of a cloud of heavy interacting particles (or drops) in a viscous fluid are considered. A new approach suitable for analytical and numerical tracing the changes in the structure of the flows in a two-component suspension under continuous transition from the Stokes
settling (for the case of a cloud of large particles) to the Rayleigh–Taylor flows and heavy diapirs (for the case of a cloud of small particles) is suggested. It is numerically and analytically shown that the both regimes are the different limiting cases of the sedimentation convection in suspensions.

Физика Земли. 2019;(2):15-30
views
Approximation approach in various modifications of the method of linear integral representations
Stepanova I.E., Kerimov I.A., Yagola A.G.
Abstract

The specificity of applying the approximation approach to solving the linear and nonlinear inverse problems of geophysics, geodesy, and geomorphology is discussed. Within the paradigm proposed by V.N. Strakhov, practically all geophysical problems can be reduced to the 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. Based on the combined approximations of the topography and geopotential fields, it is possible to determine 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 for numerical solving the inverse problem on the distributions of carriers of mass equivalent in terms of the external field in the ordinary three-dimensional space and in the four-dimensional space is described.

Физика Земли. 2019;(2):31-46
views
Analysis of long-term observations of the groundwater level In an aseismic region
Lyubushin A.A., Kazantseva O.S., Manukin A.B.
Abstract

The results of the analysis of continuous precise time series of atmospheric pressure and groundwater level fluctuations in a well drilled to a depth of 400 m in the territory of Moscow are presented. The observations are remarkable in terms of their duration of more than 22 years (from February 2, 1993 to April 4, 2015) and by the sampling interval of 10 min. These long observations are suitable for exploring the stationarity of the properties of hydrogeological time series in a seismically quiet region, which is important from the methodological standpoint for interpreting the similar observations in seismically active regions aimed at earthquake prediction. Factor and cluster analysis applied to the sequence of multivariate vectors of
the statistical properties of groundwater level time series in the successive 10-day windows after adaptive compensation for atmospheric pressure effects distinguish five different statistically significant states of the time series with the transitions between them. An attempt to geophysically interpret the revealed states is made. Two significant periods – 46 and 275 days – are established by spectral analysis of the sequence of the transitions times between the clusters.

Физика Земли. 2019;(2):47-67
views
The use of parallel computing for the high-resolution determination of earthquake source parameters
Fomochkina A.S., Bukchin V.G.
Abstract

Alongside the determination of the focal mechanism and source depth of an earthquake by direct examination of their probable values on a grid in the parameter space, also the resolution of these determinations can be estimated. However, this approach requires considerable time in the case of a detailed search. A special case of a shallow earthquake whose one nodal plane is subhorizontal is an example of the sources that require the use of a detailed grid. For studying these events based on the records of the long-period surface waves, the grids with high degree of detail in the angles of the focal mechanism are required. We discuss the application of the methods of parallel computing for speeding up the calculations of earthquake parameters and present the results of studying the strongest aftershock of the Tohoku, Japan, earthquake by this approach.

Физика Земли. 2019;(2):68-75
views
Structure formation peculiarities at early stage of Antarctic–Australia separation based on physical modeling
Dubinin E.P., Leichenkov G.L., Grokholsky A.l., Sergeeva V.M., Agranov G.D.
Abstract

The paper addresses crustal formation in the Australian–Antarctic basin at the early period of separation of Australia and Antarctica. The study covers long rifting (~160–80 Ma), ultraslow spreading (~80–45 Ma) with the formation of proto-oceanic, mainly ultrabasic crust, spreading (~45-40 Ma), and stationary spreading at medium velocities (after 40 Ma). The different stages of oceanic opening are clearly expressed in the changes of basement morphology (the top of the second oceanic layer) on seismic profiles. Physical modeling is used to reveal the peculiarities in the surface morphology of the oceanic (magmatic) crust which developed in the transitional conditions from ultraslow to slow and medium spreading. Our experiments established that (1) the presence of a stronger block in the pre-breakup model lithosphere in the pathway of the propagating rift faults can significantly affect the geometry of the spreading axis in its vicinity and lead to the development of transversal structures and a highly rugged relief; (2) under the conditions of ultraslow ocean accretion, numerous jumps of the spreading axes occur; (3) the temporary cessation of spreading leads to the development of linear high-amplitude uplifts corresponding to amagmatic ridges in the natural conditions.

Физика Земли. 2019;(2):76-91
views
Signs of the record of geomagnetic reversal in permian–triassic trap intrusions of the Ergalakhsky complex, Norilsk region
Latyshev A.V., Ulyakhina P.S., Krivolutskaya N.A.
Abstract

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

Физика Земли. 2019;(2):92-110
views
The history and state-of-the-art of the studies of native iron in terrestrial and extraterrestrial rocks
Pechersky D.M., Markov G.P.
Abstract

A brief review on the history of studying native iron in terrestrial rocks and meteorites is presented. The synthesis and systematization of extensive data on the distribution, composition, and grain size of metal iron particles in sediments, other terrestrial rocks, and meteorites obtained by thermomagnetic analysis with heating to 800 °C combined with microprobe analysis are described. The studies show that iron
particles in all the studied sediments typically have extraterrestrial origin. Based on the statistical analysis of the thermomagnetic data, a number of indications (statistical regularities) are proposed testifying to the overwhelmingly extraterrestrial origin of iron particles in sediments. The similarity of the formation conditions of terrestrial and extraterrestrial metal iron particles makes it possible to suggest a petromagnetic scheme for the structure of planets based on the distribution of metal iron in them.

Физика Земли. 2019;(2):111-122
views
Archaeomagnetic studies at Schmidt institute of physics of the earth, Russian Academy of Sciences: history and main results
Nechasova I.E., Pilipenko O.V.
Abstract

The archaeomagnetic studies carried out at the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS) provided an important contribution to the international studies of the main magnetic field of the Earth for the past few thousand years. Extensive data on the intensity of geomagnetic field in the past 8000 years were obtained. Four most representative and long time series of the data have been constructed for Eurasia for the Iberian Peninsula, the Caucasus, Central Asia, and Siberia. Unique studies having no analogues in international research have been carried out into rapid variations in the geomagnetic field intensity with characteristic times starting from several tens of years. Based on the analysis of the international data on the ancient geomagnetic field, the spectrum of the variations in the geomagnetic field intensity with the periods ranging from decades to millennia was established and the characteristics of
the variations whose superposition can describe the pattern of the changes of the geomagnetic field intensity were determined. It was found out that variations with different characteristic times have a differently directed drift, and the “main oscillation” with a characteristic time of 8000 years has an eastern drift.

Физика Земли. 2019;(2):123-136
views
An overview of wellbore methods of investigating stress state of the upper layers of the earth’s crust
Dubinya N.V.
Abstract

The wellbore methods for studying the stress-strain state of the upper layers of the Earth’s crust are overviewed. Some main methods for stress estimating from wellbore data are presented alongside with the analysis of their applicability and uncertainty appearing after their application. The reconstruction of stress profiles along the well trajectory based on the data on wellbore breakouts, drilling-induced tensile fractures, elastic wave propagation in the well surrounding the rock masses, and regularities in the spatial orientation and distribution of natural fractures is discussed. The estimation of stress state parameters based on minifracs and leakoff tests as well as on strain recovery techniques from the oriented core samples from wells is described.

Физика Земли. 2019;(2):137-155
views
Seismotectonic setting of the earthquake of august 7, 2016 and its aftershocks
Sanina I.A., Ivanchenko G.N., Gorbunova E.M., Konstantinovskaya N.L., Nesterkina M.A., Gabsatarova I.P.
Abstract

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

Физика Земли. 2019;(2):156-167
views
Tidal generated electric field in the multi-layer structure and the possibilities of its employment for deriving the elastic properties and permeability of the subsurface formations
Alekseev D.A., Gokhberg M.B.
Abstract

An analytical solution of pore pressure equations with a perturbation source in the form of lunar-solar tidal deformations is generalized to the case of a model with the arbitrary number of layers. The electric field of electrokinetic nature is calculated. The sensitivity of pore pressure and its vertical derivative to the elastic properties and permeability of rock strata is evaluated. The program code for solving the inverse problem capable of recovering the Biot modulus and Biot coefficient as well as permeability coefficient in a horizontally layered model is developed. The possibilities of mapping these parameters are discussed including their study from the borehole measurements of the vertical electric field of electrokinetic origin.

Физика Земли. 2019;(2):168-180
views
Surface impedance of electromagnetic field excited by a grounded horizontal antenna in the Earth–ionosphere waveguide
Tereshchenko E.D., Tereshchenko P.E.
Abstract

Analytical formulas for the tangential components of extremely-low-frequency (ELF) electromagnetic field in the Earth–ionosphere plane waveguide excited by a grounded linear horizontal antenna are obtained. The behavior of surface impedance is studied as a function of electrodynamic characteristics of the waveguide and the distance from the source. It is shown that 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 the ELF and lower-frequency magnetic field and, thus, on the impedance at the distances shorter 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.

Физика Земли. 2019;(2):181-189
views
Grigory Aleksandrovich Gamburtsev: a person and a scientist
Gamburtsev A.G.
Abstract

The paper is devoted to the outstanding scientist, academician Grigory Aleksandrovich Gamburtsev, a pioneer in creating seismic methods for mineral prospecting and exploration in the USSR, a founder of the scientific schools and research directions, a theorist and experimentalist.

Физика Земли. 2019;(2):190-200
views

This website uses cookies

You consent to our cookies if you continue to use our website.

About Cookies