No 1 (2019)

ARTICLES
Problems of interaction of geospheres and physical fields in near-surface geophysics
Adushkin V.V., Spivak A.A.
Abstract

The main directions and problems addressed by near-surface geophysics – the new currently actively developing scientific discipline – are formulated and discussed. A combined approach is proposed for exploring the geospheres’ interactions at the Earth’s crust – atmosphere boundary where mass- and energy exchange between the internal and external geospheres is most intense and for studying the interactions and transformations of the geophysical fields in the surface zone of the Earth including its biosphere. New results obtained in the studies of inter-geosphere interactions and physical fields of the Earth are presented. It is emphasized that establishing the geophysical conditions of human environment and characteristics of manmade activity is of great importance.

Физика Земли. 2019;(1):4-15
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Receiver function seismology
Vinnik L.P.
Abstract

The application results of the receiver function technique are briefly outlined. The topography of the main seismic boundaries in the mantle transition zone is evaluated with resolution of about 3 km in depth and about 200 km laterally. The maximal amplitudes of depth variations of the main boundaries reach tens of kilometers. The mantle transition zone thinning in the hot spots and the respective increase in temperature by ~100 °C is established. In several regions, two low-velocity layers are revealed in the mantle transition zone, one directly above the 410-km seismic discontinuity and another at a depth of 450 to 500 km. The origin of the first layer is associated with dehydration in the mantle plumes during olivine – walesite phase transformation. The increase in the S-wave velocity at the base of the second layer can explain the observations of the so-called 520-km boundary. The traditional approach to studying the structure of the crust and upper mantle is from surface waves. Receiver functions can provide higher resolution at the same depths when a combination of P- and S-wave receiver functions is used. This type of results was obtained for Fennoscandia, Kaapvaal craton, Indian shield, Central Tien Shan, Baikal rift zone, the Azores, Cape Verde Islands, and the western Mediterranean. S-receiver functions were used in the studies of the lunar crust. The joint P- and S-receiver function inversion provides robust estimates of the parameters of seismic boundaries including weak discontinuities such as the lithosphere – asthenosphere interface of cratons. The parameters determined from receiver functions include the P- to S-wave velocity ratio. In a few regions, a very high (> 2.0) velocity ratio is observed in the lower crust, probably indicating the presence of a fluid with high pore pressure. Receiver functions allow estimating the parameters of azimuthal anisotropy as a function of depth. The changes of the parameters with depth make it possible to distinguish the active anisotropy associated with recent deformations from the frozen anisotropy – the effect of the past tectonic processes.

Физика Земли. 2019;(1):16-27
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Thermal regime of the earth’s lithosphere and the mantle: geothermal studies at IPE RAS
Gliko A.O., Parphenuk I.O.
Abstract

The paper is devoted to a historical retrospective of the development of geothermal research in the former Soviet Union. The detailed history of the Laboratory of geothermics at the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS) from the mid-1950s to the mid-1980s when a full range of geothermal studies were conducted by the laboratory is presented. The main results with the special focus on the world-level achievements made by IPE RAS in this field are outlined. The second part of the paper addresses the key recent results including the theoretical studies of heat and mass transfer and numerical modeling of mantle convection.

Физика Земли. 2019;(1):28-41
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Geoinformatics and systems analysis in geophysics and geodynamics
Gvishiani A.D., Kaftan V.I., Krasnoperov R.I., Tatarinov V.N., Vavilin E.V.
Abstract

The paper is devoted to the application of geoinformatics and systems analysis methods for processing and interpretation of geospatial data in geophysics and geodynamics. The modern uses of observations with Global Navigational Satellite Systems as a main source of geospatial data are discussed. The advances in the interpretation of geomagnetic data are described and basic points of systems analysis are presented in this context. The systems analysis in geophysics and geodynamics is illustrated by the approaches to estimating and forecasting the stability of structural-tectonic blocks of the Earth’s crust aimed at geoecologically safe burial of high-level radioactive waste in the Nizhne-Kanskii granitoids massif (Krasnoyarsk krai).

Физика Земли. 2019;(1):42-60
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Comparative planetology in IPE RAS
Zharkov V.N., Gudkova T.V.
Abstract

The review of the studies on comparative planetology carried out in the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences is presented. The obtained results are described in accordance with the study objects: the Moon, terrestrial planets, Venus and Mars, Phobos and Deimos-moons of Mars, giant planets and their moons.

Физика Земли. 2019;(1):61-77
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Recent geodynamics: from crustal movements to monitoring the critical objects
Kuzmin Y.O.
Abstract

The evolution of the views on the subject and methods of recent geodynamics over the past fifty years is outlined. Metrological provision of the results obtained by repeated observations by means of ground-based and satellite geodesy is discussed. The substantial dependence of the main characteristics of recent geodynamical processes on the degree of spatiotemporal detail of the observational systems is demonstrated.

A possible solution of the paradoxes of large and small strain rates which were detected in the studies at geodynamical sites in seismically active and aseismic regions is proposed. To explain the anomalous deformational activity on the platform faults, the mechanism of parametric excitation is suggested. According to this mechanism, the time fluctuations in the internal parameters of a fault zone (stiffness, pore pressure, friction coefficient) create local strain anomalies under quasi static external loading.

The results of strain monitoring are demonstrated by the example of a shelf oil field. It is substantiated that the geodynamical testing sites are a universal instrument for exploring recent deformational processes which offers a unified framework for establishing the spatiotemporal structure of different-scale geodynamical phenomena addressed in the fundamental and applied studies.

Физика Земли. 2019;(1):78-103
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Topical problems in the theory of planet formation: formation of planetesimals
Makalkin A.B., Ziglina I.N., Artyushkova M.E.
Abstract

The development of the Earth’s and planets formation theory over 70 years is considered with a special focus on the history of development of this theory at the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS) where this direction of research was founded by Otto Schmidt. The state of the art of the theory is outlined. In particular, the planetesimals formation problem currently belonging to the key unsolved issues in the theory of planet formation is discussed. Recent results of the studies aimed at solving this problem at IPE RAS are presented.

Физика Земли. 2019;(1):104-121
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Geodynamic modeling of the process of formation and evolution of lithospheric structures: experience of Schmidt institute of physics of the earth RAS
Mikhailov V.O., Timoshkina E.P.
Abstract

Key results of numerical geodynamic modeling of the structures of the lithosphere at the Institute of Physics of the Earth of the Russian Academy of Sciences are presented. Even in the very first models, the aim of these studies was to describe the time evolution of the boundaries of the layers composing the geological structures which is required for correlating the modeling results to the geological and geophysical data. In 1983, the equation of motion for the upper boundary of the model was complemented by the allowance of sedimentation and erosion. This equation provided the basis for building the geodynamic models of the formation of various types of sedimentary basins and made it possible to mathematically analyze the problem of estimating the rates of paleotectonic movements from thickness, age, and facies composition of sedimentary layers.

New data on the formation and evolution processes of large-scale tectonic structures are obtained in the model of a rheologically stratified Earth’s boundary layer, asymptotically linked to mantle convection model. In particular, the role of the small-scale convection in the formation of lithospheric structures in the tectonic settings of extension and compression has been explored. The numerical results clearly demonstrate the key role of the small-scale asthenospheric convection in sedimentary basin formation (post-rift, on passive continental margins, in foredeep basins). The constructed models served as the basis for interpretation of heterogeneous geological and geophysical data in the context of geodynamic models. The examples of statement of inverse problems are presented and the relevant bibliography is provided.

Физика Земли. 2019;(1):122-133
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Evolution of views on the structure of sources of strong earthquakes at the end of XX and beginning of XXI centuries
Rogozhin E.A.
Abstract

The paper addresses the evolution of scientific views on the structure of the sources of strong earthquakes at the end of the 20th and beginning of the 21th century in Russia. The scientific concepts that emerged in the main developed countries initially typically lacked a clear and consistent understanding of the structure of sources of the strongest seismic events. In the 1950s, at the Schmidt Institute of Physics of the Earth of the USSR Academy of Sciences, G.A. Gamburtsev formulated a hypothesis of a long-term (a few hundred years) stability of seismic regime of a system of seismic sutures. The recently studied earthquakes have their sources in the regions of the large faults. The earthquakes of larger magnitudes have more extended and structurally more complex sources. Some sources in the considered cases are relatively simple to reconstruct (they encompass the fault planes of the large faults, e.g., the Spitak source, M = 6.8). Other sources are more complex; they are formed in the disjunctive nodes or encompass the crustal blocks. For example, the seismic source of the Altai earthquake (M = 7.3) has a volumetric structure and is developed along the boundaries of the large seismogenic blocks. The Wenchuan earthquake (M = 7.9) has a most complicated source which looks as a three-dimensional (3D) structure composed of a few crustal blocks framed by two extended northeast striking faults and separated by the northwesterly trending transverse fault. The structurally different sources differently manifest themselves in the pattern of seismic dislocations on the surface and in the distribution of aftershock hypocenters at depth. The anomalously low velocity “pockets” identified by local seismic tomography in the source areas of the Spitak and Altai earthquakes which accompany the main and secondary faults at depth are likely to be the zones of dynamic control of these faults. The breaked near-fault zones abundant with cracks and fractures are the severely looze inclusions in the crustal rocks hampering the propagation of seismic waves. Therefore, the P-waves in these pockets propagate at lower velocities than in the undamaged geological medium. The paleoseismological studies of seismic faults in trenches have shown that the strong earthquakes have occurred in the same sources in the past and the recurrence period of the strongest seismic events ranges from a few hundred to a few thousand years. Thus, the combined studies of the source zones of the strongest earthquakes conducted in the past decades in the different regions of Eurasia have shown that Gamburtsev’s hypothesis has remained relevant.

Физика Земли. 2019;(1):134-148
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Dependences of the Omori and Gutenberg–Richter parameters
Smirnov V.B., Ponomarev A.V., Stanchits S.A., Potanina M.G., Patonin A.V., Dresen G., Narteau C., Bernard P., Stroganova S.M.
Abstract

Laboratory experiments on studying the aftershock regime are carried out with sandstone specimens under different axial loading and uniform compression and constant pore pressure. The aftershock sequences are modeled by the scenario of stepwise increasing axial loading of a specimen with strain control ensuring regular generation of aftershock sequences. The experiments are conducted on intact specimens and on the specimens with preliminarily formed shear macrofractures simulating natural faults. The experiments were conducted with multichannel recording of the acoustic emission (AE) signals which made it possible to locate the AE sources. Several types of the dependence of the acoustic activity relaxation parameters (parameters p and c of the modified Omori law and the Gutenberg–Richter b-value) on the level of acting stresses are revealed. The b-value decreases with the growth of axial stresses at all levels of uniform compression. In the case of fracture on the preexisting fault, the Omori relaxation parameter p increases with the growth of axial stresses whereas parameter c (the time delay before the onset of relaxation) decreases with the growth of axial stresses and increases with the rise of the level of uniform compression. In the case of a fracture of an undamaged specimen, parameter p remains unchanged as the axial stresses grow, whereas parameter c increases slightly. Parameter variations in the case of a complex stress state with both varying deviatoric (differential stresses) and spherical parts (effective pressure) of the stress tensor take on a unified form when expressed in terms of Coulomb stresses. It is hypothesized that the time delay of the aftershock activity relaxation is determined by the kinetics of fracture in accordance with the kinetic concept of strength in solids. This hypothesis is supported by exponential dependence of parameter c on stresses and on the effective strength of the medium revealed in the experiments. Under this hypothesis, the dependences of parameter c on the Coulomb stresses can be unified for different effective strength values with the use of Zhurkov’s formula for durability of materials. The obtained parameter estimates for the dependence of c on strength and stresses suggest that the c value is determined by the difference of the strength and the acting stresses, indicating how far the stress state of the medium is from the critical state corresponding to the ultimate strength.

Физика Земли. 2019;(1):149-165
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Avalanche unstable fracturing formation model
Sobolev G.A.
Abstract

The basic ideas of the avalanche unstable fracture formation (AUF) model were for the first time presented by the scientists of the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences at the Assembly of International Union of Geodesy and Geophysics in Moscow in 1971 and published in a special issue of Tectonophysics in 1972. Subsequently, numerous laboratory and in situ experiments have validated and elaborated the AUF model. The model builds on the fundamental principles of the long-term strength physics. The model is independent of the scale of a phenomenon and can be used for describing the rupture preparation not only in the earthquake sources of different energy levels but also for the dynamic events in mines and for the failures of engineering structures under long-term loading. Based on the model, the formation of the widespread en-echelon fracture systems is explained. The earthquake preparation process develops gradually suggesting the possibility to forecast the time of a future seismic event. The model substantiates self-evolution of the earthquake process.

Физика Земли. 2019;(1):166-179
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Problems of global geodynamics
Trubitsyn V.P.
Abstract

Global geodynamics is determined by thermal convection in the mantle which manifests itself on the surface by movements, relief, heat flow, and volcanism. Thermal convection in the Earth is complicated by the fact that the lithosphere is broken into rigid plates, the crust is broken into six separate floating continents and a number of islands, on the mantle bottom there are two giant piles of heavy material, at high convection intensity the ascending convective flows acquire a plume shape, and phase transformations take place in the mantle. The impacts of many factors on the mantle structure have been thoroughly studied and fairly well understood. It is pertinent to reconcile the new data on phase transformations at depths of 650 to 700 km with the seismic data on the positions of these boundaries. The ultimate problem of global geodynamics has not yet been solved; the three-dimensional structure of the whole-mantle flows, consistent with the observations in geophysics, geochemistry, geology, and numerical modeling, is not known even on a semischematic level.

Физика Земли. 2019;(1):180-198
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Impact of earthquakes and tsunamis on the ionosphere
Shalimov S.L., Rozhnoi A.A., Solov`eva M.S., Ol`shanskaya E.V.
Abstract

Fairly complex processes of lithosphere–ionosphere interactions can be explored by diagnosing the outer envelopes of the Earth with the use of global satellite navigational systems and equally global network of ground receivers and very-low-frequency transmitters. The earthquake and tsunami impacts on the ionosphere are the example of these processes. The current advances in the studies of these processes are briefly outlined.

Физика Земли. 2019;(1):199-213
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Analysis of the hypothesis of a giant gaussian process as a means for describing secular variations of the geomagnetic field vector
Scherbakov V.P., Khokhlov A.V., Sycheva N.K.
Abstract

The consistency of the empirical data on paleointensity and paleoinclinations contained in the BOROKPINT paleointensity world database with the Geocentric Axial Dipole (GAD) hypothesis and Giant Gaussian Process (GGP) model describing the geomagnetic field variations in the Brunhes epoch is tested. The calculations are based on the geomagnetic field potential representation by the sum of spherical functions of spatial coordinates with random coefficients, enabling computer simulation of the data with the given statistical characteristics of the coefficients. The estimates show that the Kolmogorov–Smirnov and Anderson–Darling tests reject the GAD hypothesis in its canonical form. The extension of GAD to GGD with nonzero time-average quadrupole and octupole terms makes the paleointensity and paleoinclination data to comply with GGP model realizations; however, these models are mutually exclusive because of mutual inconsistency of their parameters. Testing the paleoinclination data against GDP model shows that a small correction to the purely dipole component of the geomagnetic field should be introduced. At the same time, the paleointensity data analysis suggests that these data highly probably agree with GGP models with a high quadrupole contribution making up 1/3 of the dipole coefficient, which is strongly at odds with the parameters of the model corresponding to paleoinclination data. This inconsistency is most likely to be due to the artifacts associated with incorrect paleointensity determinations; however, this interpretation does not explain the causes of the strong latitudinal dependence of the intensity of the Virtual Axial Dipole Moment (VADM) which follows from the empirical data.

Физика Земли. 2019;(1):214-228
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