Models of the Earth’s plasmapause position

正The plasmasphere is a region of relatively dense(~10–10000 cm~(–3))plasma,surrounding the Earth and extending to distances of about five Earth radii(R_E).It is filled with large amount of cold(~1 e V)plasma originated from the Earth’s ionosphere and co-rotating with the Earth due to the large scale co-rotation electric field.The outermost     

Inertial effects in the Earth’s crust and magnetosphere

A review of studies devoted to the problem of exciting magnetic signals in the crust associated with the formation of the major rupture in an earthquake source and with the propagation of seismic waves was given in [Sgrigna et al., 2004]. However, this review contains incorrect citations from original papers and several erroneous statements concerning inertial and inductive mechanisms of conversion of the energy of rock motion into magnetic field energy. These mistakes are analyzed in the present paper. The formal and physical similarity between seismomagnetic waves in the crust and Alfvén waves in the magnetosphere is used in the analysis. A comparative analysis of the inertial and inductive mechanisms of seismomagnetic field generation is performed. The Cherenkov criterion of Alfvén wave generation due to the ionospheric effect of acoustic waves from earthquakes and explosions is derived. Attention is also given to nonlinear phenomena (nonlinearity of a mechanomagnetic conversion in the crust and anharmonicity and self-focusing of Alfvén waves in the magnetosphere).     

Rigidity of the fault zones in the Earth’s crust estimated from seismic data

Nonlinear effects in seismic wave propagation are analyzed to determine the mechanical rigidity of different-order faults that thread the tectonic structures in the central part of the East European platform (Moscow syneclise and Voronezh Crystalline Massif) and the fault zones of the Balapan and Degelen mountain regions in Kazakhstan (the Degelen magmatic node in the Central Chingiz zone). The dependency of the rigidity of the fault zone on the fault’s length is obtained. The rigidity of the tectonic structures is found to experience well-expressed temporal variations with periods of 13–15 days, 27–32 days, and about one year. In the different-order fault zones, the amplitudes of both normal k _n and the shear k _s rigidity for semimonthly, monthly, and annual variations can span a factor of 1.3, 1.5, and 2.5, respectively.     

Correlation of variations in the thermal neutron flux from the Earth’s crust with the Moon’s phases and with seismic activity

The results of the long-term recording of thermal neutron flux near the Earth’s surface with the use of an unshielded scintillation thermal-neutron detector are presented. The data obtained indicate the presence of periodic variations in the thermal neutron flux with the lunar diurnal and the lunar monthly periods. A hypothesis about the existence in the Earth’s crust of radon-neutron tidal variations in the concentration of thermal neutrons, correlated with the Moon’s phases and which have the gravitational origin, is formulated and confirmed experimentally. A simple mathematical model is proposed, which satisfactorily describes the observed variations. The case of the anomalous behavior of thermal neutrons is presented, which correlates with the high local seismic activity.     

Induced seismicity and the possibilities of controlled relaxation of tectonic stresses in the Earth’s crust

Natural and anthropogenic impacts on seismicity are considered. Taking into account the importance of the discussed problem, the authors propose to open the discussion on the questions considered. In this connection a wide circle of known experimental data is considered, which are indicative of the possibility in principle of active impact on the seismogenic medium for the smooth relieving of accumulated tectonic stresses in the Earth’ s crust. The reasoning is presented of one of the promising ways of the smooth controlled relaxation of the accumulated tectonic stresses in the Earth’s crust at the places of the probable onset of strong earthquakes due to a considerable increase in the plastic slips, which facilitate the decrease of the number and energy of earthquakes. The approach proposed is based on the results of the works on the excited seismicity, obtained in different regions of the Earth. Special attention is given to the most detailed long-term investigations of the excited seismicity in the region of the reservoir of the Nurek hydroelectric station in Tadzhikistan and in the neighborhood of the actively mined Romashkinskoe oil deposit in the Republic of Tatarstan. The results of the laboratory investigations of the behavior of samples made of materials of crystalline and amorphous structures under the action of pressure and vibration are invoked for the substantiation of the physical nature of the observed effects. For the reduction of seismic hazard, it is proposed to use vibration actions and water injection in the bore holes at the places of the expected seismic catastrophes in a time mode matched with the tidal motions of the Earth.     

Comparative Assessment of Global Models of the Earth’s Gravity Field

Izvestiya, Physics of the Solid Earth - Abstract—Empirical comparative study of the modern global models of the Earth’s gravity field (EGF) in the form of geopotential spherical...     

Distribution relations of tectonical stresses in the upper part of the Earth’s crust

Due to an analysis of the data in the literature on stress measurements in mining sites in the former Soviet Union, including those performed in the mines of the Kola Peninsula and the Kola Superdeep Borehole SG-3, the subhorizontal tectonic stresses were reported to exceed the lithostatic stresses. As a rule, tectonic stresses are attributed to the interaction boundaries of blocks of different sizes: from lithosphere platforms to blocks of IV–V ranks.     

A simple smoothed velocity model of the uppermost Earth’s crust derived from joint inversion of Pg and Sg waves

The paper presents some results of seismic experiments carried out on the territory of northern Moravia and Silesia, roughly delimited by the coordinates 16°E–19°E and 49°N–51°N. The experiments were aimed at compiling a velocity model of the uppermost Earth’s crust using the database of arrival times of Pg and Sg waves recorded at a fairly large number of seismic stations, which enabled us to produce a simple 1D-layered velocity model of the region. The velocity model was computed using the traditional tomographic iterative process composed of consecutive solutions of linear equations. Based on the analysis of velocity distribution, it was found that the velocities of Pg and Sg waves increase from about 5.9 and 3.3 km/s at the surface, to about 6.1 and 3.5 km/s at a depth of 11 km, respectively.     

The Earth’s crust of the deep platform basins in the Northern Eurasia and their origin

Several large basins with a depth up to 15–20 km are revealed in the platform regions of Northern Eurasia—the Pre-Caspian, Vilyui, Pur-Gydan, and Kara–Barents platforms. All these basins have two structural features in common: they all have a rounded shape with steep walls and are marked with the reduced thickness of the Earth’s crust. With the basins' depth of 15–20 km, the basement top is flat and has an almost horizontal surface. The basins differ by the average seismic velocities in the crystalline crust which vary from 6.2–64 to 6.8–7.0 km/s. Another distinction is the type of the crystalline crust ranging from continental with a thick granite-gneiss layer to suboceanic, represented by the basite layer. For explaining the formation of these basins, we suggest a combined petrophysical model which includes several geodynamical processes of different intensity: rifting, basification, and eclogitization of the Earth’s crust.The model also takes into account the process of material outflow from beneath a basin through the midcrustal layer of increased porosity and fluid saturation. This accounts for the strong reduction of the granite-gneiss layer with the preservation of the basement’s flat surface and for the formation of significant source areas of clastic material around the basin. The formation of these basins requires an extensive and sufficiently laterally uniform and longoperating energy source. The intrusion of the mantle material saturated with fluids into the bottom portions of the crust or, simply, the long-lasting inflow of the deep fluids are the most probable sources of this kind.     

Lunar–solar tide effects in the Earth’s crust and atmosphere

The gravitational interaction in the Earth–Moon–Sun system is considered from the standpoint of influencing the formation of time variations in the geophysical fields and some natural processes. The analysis of the results of instrumental observations revealed the main periodicities and cycles in the time variations of subsoil radon volumetric activity with the same periods as the vertical component of the variations of the tidal force. The amplitude modulation of seismic noise by the lunar-solar tide is demonstrated. It is shown that the intensity of relaxation processes in the Earth’s crust has a near-diurnal periodicity, whereas the spectrum of groundwater level fluctuations includes clearly expressed tidal waves. Based on the data on the tilts of the Earth’s surface, the role of tidal deformation in the formation of the block motions in the Earth’s crust is analyzed. A new approach is suggested for identifying tidal waves in the atmosphere by analyzing micropulsations of the atmospheric pressure with the use of adaptive rejection filters.     

Subvertical clusters of earthquake hypocenters unrelated to the tectonic structure of the Earth’s crust

The existence of a subvertical pillar-like cluster of earthquake hypocenters is established in the central part of the Garm geodynamic test area (Tajikistan). Seismotectonic deformation of the subvertical uniaxial extension prevails in the lower part of the cluster. This cluster is characterized by the absence of any relation to elements of the tectonic structure of the region. It is supposed that this element of the seismogenic structure of the region represents a channel of supply of deep fluids. Clusters of aftershock sources, close in morphology and position, are known in connection with the Altai, Neftegorsk, and Kultuk earthquakes. The subvertical but flattened-out in plan accumulations of aftershocks, unrelated to any elements of the tectonic structure of the Greater Caucasus, correspond to the Dagestan earthquake. Some other accumulations of earthquake hypocenters, so-called nests, such as the Vrancea and Hindu Kush ones, can be probably regarded as formations of a similar type.     

Marine debris review for Latin America and the wider Caribbean region: from the 1970s until now, and where do we go from here?

The available literature on marine debris from Latin America and the Wider Caribbean Region was collected and linked, reviewing their methodologies and principal results (quantities, composition and spatial-temporal patterns). The study region comprises 52 coastal countries of which only 14 had registers of works on marine debris. A total of 70 works were available and 69 had their full contents accessed. Brazil dominated the available literature with 70% of the documents. Beaches were the most studied environment, and plastics the prevalent form of contamination in the whole region. The exposure of marine biota (species, type of contact, consequences) was highlighted. The studied region, although still little exploited by this sort of research, shows the same contamination patterns observed world-wide. We also contacted 40 researchers in the area, collecting scientific contributions, opinions and suggestions for improvement of this research field. Further advances and new (urgently needed) lines of research are also discussed.     

Spectral expressions for modelling the gravitational field of the Earth’s crust density structure

We derive expressions for computing the gravitational field (potential and its radial derivative) generated by an arbitrary homogeneous or laterally varying density contrast layer with a variable depth and thickness based on methods for a spherical harmonic analysis and synthesis of gravity field. The newly derived expressions are utilised in the gravimetric forward modelling of major known density structures within the Earth’s crust (excluding the ocean density contrast) beneath the geoid surface. The gravitational field quantities due to the sediments and crust components density contrasts, shown in numerical examples, are computed using the 2 × 2 arc-deg discrete data from the global crustal model CRUST2.0. These density contrasts are defined relative to the adopted value of the reference crustal density of 2670 kgm⁻³. All computations are realised globally on a 1 × 1 arc-deg geographical grid at the Earth’s surface. The maxima of the gravitational signal due to the sediments density contrast are mainly along continental shelf regions with the largest sedimentary deposits. The corresponding maxima due to the consolidated crust components density contrast are over areas of the largest continental crustal thickness with variable geological structure.     

On conditions of magmatism origin and role of volcanic activity in the thermal regime of Earth’s crust

Bulletin of Volcanology -     

Effects of lunar-solar tides in the variations of geophysical fields at the boundary between the Earth’s crust and the atmosphere

Extraterrestrial forcing of natural environmental processes by gravitational interaction between the Sun, the Moon, and the Earth is considered. Based on the instrumental data, the main periodical components and cycles are identified in the time variations of some geophysical fields at the boundary between the Earth’s crust and the atmosphere. Correlation analysis shows that the lunar-solar tides are the key factor responsible for diurnal and quasi-biweekly variations in the ground electric field, radon emanation, water level in wells, and microseismic vibrations. The tidal influence on the various-scale movements of the blocks of the Earth’s crust is analyzed. In the context of the vertical, lateral, and rotational motion of crustal blocks, which is very important for the platforms, a new, precession-like type of displacements is revealed. These movements develop as a result of the nonsynchronous tidal responses of the block and the adjacent interblock gaps or tectonic structures whose strength and strain properties are different in different directions.     

Seismotectonic destruction of the Earth’s crust in the zone of interaction of the northeastern side of the Baikal rift and the Aldan-Stanovoy block

The paper presents the modern structural-tectonic pattern and a tectonodynamic model of the zone of interaction of the most seismically active northeastern side of the Baikal rift zone (BRZ) and the conjugate system of seismogenic structures of the Aldan-Stanovoy block, where disastrous events with M ≥ 6.0 have been reported. Regularities in the structural formation of active faults and their kinematics are discussed. The faults form block structures accumulating significant tectonic strain. Motions between large tectonic blocks cause sudden release of the strain, which results in catastrophic events (M ≥ 6.0) with focal mechanisms of definite kinematic type.     

Using the Digital Models of Gravity Anomalies for Zoning of the Earth’s Gravity Field

This paper addresses the questions associated with using the models in regioning the Earth’s gravity field depending on its roughness and type of anomalies. A formalized technique for zoning based on the analysis of the intensity and variability of gravity anomalies is suggested. The suggested technique includes preprocessing the initial gravity anomalies aimed at eliminating the noise component; partitioning the studied region into the elementary segments; calculating the primary characteristics of the complexity and roughness (the intensity and variability of gravity anomalies) for each segment; and, based on these characteristics, classifying each segment into a particular category of complexity. The proposed system of classification of segments relies on the use of three classes of intensity and three classes of variability of gravity anomalies and four categories of complexity of the regions, which are derived from these classes. As a result of applying the technique, the mapped territory is subdivided into the regions that are uniform in terms of their geophysical properties. The developed technique is used for comparing the quality of the different digital models of gravity anomalies, including the Russian RGM model (A.P. Karpinsky Russian Geological Research Institute (VSEGEI)) and the WGM model (Bureau Gravimétrique International (BGI)) in the region of the Mongol–Okhotsk orogenic belt and Sikhote–Alin fold system. The results of the study can be used for zoning of the other geophysical fields and for planning the locations of the new survey networks for increasing the accuracy of the initial data used for compiling the maps.     

Deformation of the Earth’s crust in the Northern Tien Shan according to the earthquake focal data and satellite geodesy

For evaluating the deformations of the Earth’s crust in the Northern Tien Shan, we calculated the mode and intensity of the seismotectonic deformations (STD) for this region. The input for these calculations were the catalog data on the focal mechanisms of earthquakes, obtained by wave inversion of the signals recorded at the Kyrgyz seismic network (KNET) for the period 1994–2006. In the construction of STD maps, a modern approach to the classification of seismotectonic deformations was applied. This approach distinguishes eleven typical patterns of deformation. The areal distributions of the Lode-Nadai coefficient, as well as of the vertical component and the aspect angle of the deformed state were obtained. At the same time, based on the GPS measurements in the Northern Tien Shan during 1994–2006, the rates of dilatation and shear deformation of the Earth’s crust were estimated. A comparison between the directions of strain axes derived from the GPS data and from the earthquake focal data is carried out.     

Analysis of Current Movements and Deformations of the Earth’s Crust in Fennoscandia from GNSS Data

Izvestiya, Physics of the Solid Earth - Abstract—An analysis of the displacement rates of GNSS points indicates that the values of current deformations gradually decrease from the center of...     

Electromagnetic sounding of the Earth’s crust in the region of superdeep boreholes of Yamal-Nenets autonomous district using the fields of natural and controlled sources

Electromagnetic soundings with the fields of natural (magnetotelluric (MT), and audio magnetotelluric (AMT)) and high-power controlled sources have been carried out in the region of the SG-6 (Tyumen) and SG-7 (En-Yakhin) superdeep boreholes in the Yamal-Nenets autonomous district (YaNAD). In the controlled-source soundings, the electromagnetic field was generated by the VL Urengoi-Pangody 220-kV industrial power transmission line (PTL), which has a length of 114 km, and ultralow-frequency (ULF) Zevs radiating antenna located at a distance of 2000 km from the signal recording sites. In the soundings with the Urengoi-Pangody PTL, the Energiya-2 generator capable of supplying up to 200 kW of power and Energiya-3 portable generator with a power of 2 kW were used as the sources. These generators were designed and manufactured at the Kola Science Center of the Russian Academy of Sciences. The soundings with the Energiya-2 generator were conducted in the frequency range from 0.38 to 175 Hz. The external generator was connected to the PTL in upon the agreement with the Yamal-Nenets Enterprise of Main Electric Networks, a branch of OAO FSK ES of Western Siberia. The connection was carried out by the wire-ground scheme during the routine maintenance of PTL in the nighttime. The highest-quality signals were recorded in the region of the SG-7 (En-Yakhin) superdeep borehole, where the industrial noise is lowest. The results of the inversion of the soundings with PTL and Zevs ULF transmitter completely agree with each other and with the data of electric logging. The MT-AMT data provide additional information about the deep structure of the region in the low-frequency range (below 1Hz). It is established that the section of SG-6 and SG-7 boreholes contains conductive layers in the depth intervals from 0.15 to 0.3 km and from 1 to 1.5 km. These layers are associated with the variations in the lithological composition, porosity, and fluid saturation of the rocks. The top of the poorly conductive Permian-Triassic complex is identified at a depth of about 7 km. On the basis of the MT data in the lowest frequency band (hourly and longer periods) with the observations at the Novosibirsk observatory taken into account, the distribution of electric resistivity up to a depth of 800 km is reconstructed. This distribution can be used as additional information when calculating the temperature and rheology of the lithosphere and upper mantle in West Siberia. The results of our studies demonstrate the high potential of the complex electromagnetic soundings with natural and controlled sources in the study of deep structure of the lithosphere and tracing deep oil-and-gas-bearing horizons in the sedimentary cover of the West Siberian Platform within the Yamal-Nenets autonomous district.