Ray Tracing Methods in Seismic Emission Tomography     

I. Ya. Chebotareva 《Izvestiya Physics of the Solid Earth》2018,54(2):201-213

Highly efficient approximate ray tracing techniques which can be used in seismic emission tomography and in other methods requiring a large number of raypaths are described. The techniques are applicable for the gradient and plane-layered velocity sections of the medium and for the models with a complicated geometry of contrasting boundaries. The empirical results obtained with the use of the discussed ray tracing technologies and seismic emission tomography results, as well as the results of numerical modeling, are presented.  相似文献   

Phenomenon of Concretions Occurrence on the Ocean Bottom     

M. M. Ramazanov  A. V. Karakin 《Izvestiya Physics of the Solid Earth》2018,54(2):388-392

The paradox of the long-term existence of ferromanganese concretions on the ocean floor is considered. It is known that nodules do not sink in the less dense medium of liquefied sediments and have been located on the bottom surface since their genesis over many thousands or even millions of years. At the same time, river and sea sludge easily sucks up other objects (of the same density), which in some way fall to the bottom. We propose an original mechanism explaining this paradox, which is based on a combination of three physicochemical phenomena.  相似文献   

Deep Structure of the Zone of Tolbachik Fissure Eruptions (Kamchatka,Klyuchevskoy Volcano Group): Evidence from a Complex of Geological and Geophysical Data     

Yu. A. Kugaenko  V. A. Saltykov  A. V. Gorvatikov  M. Yu. Stepanova 《Izvestiya Physics of the Solid Earth》2018,54(3):444-465

With the use of the method of low-frequency microseismic sounding, the configuration of the magmatic feeding system of the Tolbachinsky Dol—a regional zone of areal basaltic volcanism in the southern part of the Klyuchevskoy volcano group in Kamchatka—is studied. The initial data are obtained by a stepby-step recording of the background microseismic noise in 2010–2015 within a thoroughly marked-out survey area covering the zones of fissure eruptions in 1975–1976 and 2012–2013 and, partly, the edifice of the Ploskii (flat) Tolbachik volcano. The depth sections reflecting the distributions of the relative velocities of seismic waves in the Earth’s crust are constructed. For a more reliable interpretation of the revealed deep anomalies, the results of independent geological and geophysical studies are used. The ascertained low-velocity structures are closely correlated to the manifestations of present-day volcanism. It is shown that the feeding structure of the Tolbachinsky Dol is spatially heterogeneous, incorporating subvertical and lateral pipeshaped magma conduits, closely spaced magma feeding channels, and shallow magma reservoirs. A longlived local transcrustal magma conducting zone is revealed, and regularities in the deep structure of the feeding systems of fissure eruptions are identified. The configuration of the established subvertical magma conduits permits basalts moving to rise to the surface by different paths, which, inter alia, explains the contrasting magma compositions observed during a single eruption. Thus, based on the instrumental data, it is shown that the magmatic feeding structure of the Tolbachinsky Dol has a number of specific peculiarities and is significantly more complicated than has been previously thought about the areal volcanic fields.  相似文献   

Peculiarity of the Relationship between the Seismicity and Tectonic Structure of the Pyrenees     

A. A. Lukk  V. I. Shevchenko 《Izvestiya Physics of the Solid Earth》2018,54(3):415-429

The geotectonic position of the Pyrenees mountain massif in the Alpine–Indonesian mobile belt is considered. The geological data testify to the formation of the structure of the Pyrenees in the setting of a subhorizontal compression perpendicular to the ridge. The commonly accepted interpretation considers this compression in the context of plate tectonic notions related to the collision between the Iberian and Eurasian lithospheric plates resulting from the convergence of the Eurasian and African plates. However, this interpretation is challenged by the the geodetic and seismological measurements. The GPS measurements suggest a certain cross-strike spreading rather than shortening of the Earth’s crust; the focal mechanisms of the earthquakes indicate the predominance of a subhorizontal extension perpendicular to the strike of the Pyrenees mountain range. The processes of the gravitational collapse of the mountain chain during the isostatic upwelling of the orogenic crust are considered as the most probable cause of this spreading by a number of the authors.  相似文献   

Pulsations of the Free Oscillations of the Earth in an Hourly Period Range     

G. A. Sobolev  N. A. Zakrzhevskaya  K. N. Akatova 《Izvestiya Physics of the Solid Earth》2018,54(3):393-405

The records from 161 identical broadband seismic stations located in different regions of the world after the strong earthquakes off Sumatra Island on December 26, 2004 with magnitude M = 9.1, in Chile on February 27, 2010 with M = 8.8, and the Tohoku earthquake in Japan on March 11, 2011 with M = 9.0 are studied. Oscillations with a period of ~11 h are analyzed. They are observed as pulsations in the free radial oscillations of the Earth lasting more than one week. The stations located a few hundred kilometers apart from each other demonstrate identical records. As the distance between the stations becomes larger, the structure of the records becomes different. At interstation distances of about 3800 km, the records at the stations have opposite phases, and at distances of ~7600 km, the phases coincide. This is reflected in the spatial structure of the areas of the positive and negative phases of the oscillations on the Earth’s surface. This structure recurs at the same time instant after the three considered earthquakes, which indicates that this effect is independent of the properties of the sources. The spatial positions of the areas of positive and negative phases are also not correlated to the geological conditions in the vicinity of the stations which are located both in the subduction zone and within the platform. The structure of the pulsations and their spatial distribution differ from the variations of the Earth’s tides.  相似文献   

Estimating the Influence of Geomagnetic Disturbances on the Trajectory of the Directional Drilling of Deep Wells in the Arctic Region     

A. D. Gvishiani  R. Yu. Lukianova 《Izvestiya Physics of the Solid Earth》2018,54(4):554-564

At high latitudes, sporadic geomagnetic disturbances associated with geomagnetic storms introduce significant uncertainty in measurements by borehole inclinometers during the directional drilling of deep wells. Variations in the magnetic declination may lead to significant deviations of the actual coordinates of the borehole from the prescribed trajectory. Using the methods for calculating the profile of the actual borehole, we conducted model estimates of the influence of sporadic disturbances in the magnetic declination observed during the magnetic storm of October 28–31, 2003 on the displacement azimuth and intensity of borehole bending at the given locations at the sites of two high-latitude magnetic observatories. It is shown that, unless filtered based on the data of parallel observatory measurements, the geomagnetic disturbances can lead to unacceptably large errors in the borehole inclinometer measurements and cause a borehole deflection exceeding the admissible values.  相似文献   

V. V. Beloussov and Geophysics: A Tribute on His 110th Birth Anniversary     

L. I. Ioganson  E. A. Rogozhin 《Izvestiya Physics of the Solid Earth》2018,54(4):539-553

The contribution made by V.V. Beloussov (1907–1990), an outstanding Earth scientist in the former Soviet Union and Russia, to the development of planetary geophysics is considered. Beloussov was a brilliant coordinator of international cooperation and direct inspirer of international scientific programs of paramount importance. He took up one of the key positions in organizing and holding the International Geophysical Year (IGY) in 1957–1958. In 1960, Beloussov was elected President of the International Union of Geodesy and Geophysics and proposed the project “The upper mantle and its influence on the Earth’s crust,” which subsequently became known worldwide as the Upper Mantle Project. The project underlined that the experience of the IGY should be extended to studies of the deep structure of the Earth and the processes taking place in the Earth’s interior. The fulfillment of this and the subsequent Geodynamic project resulted in a breakthrough in the knowledge about the deep structure of the Earth, particularly the structure of the oceans. Beloussov actively advocated integrating science of the Earth, geonomy, and in his scientific research sought a geonomic approach incorporating the entire complex of geological, geophysical, and geochemical data. Beloussov’s scientific heritage contains propositions that are of current importance and can be involved in modern developments of the Earth sciences.  相似文献   

On Solving the Forward Problem of Gravimetry in Curvilinear and Cartesian Coordinates: Krasovskii’s Ellipsoid and Plane Modeling     

P. S. Martyshko  I. V. Ladovskij  D. D. Byzov  A. I. Chernoskutov 《Izvestiya Physics of the Solid Earth》2018,54(4):565-573

Correcting the effects of the sphericity of the Earth in the results of the interpretation of gravimetric data is a topical issue in modern gravimetry. Estimating the error of the gravity field calculations due to the replacement of the spherical Earth model by the plane model is an important part of this problem. In this paper, a method is proposed for transforming the plane density models into spherical ones and vice versa. Algorithms for calculating the vertical component of gravity field for both model types are presented. For two extensive plane models of the Earth’s density, their transformation into spherical models is carried out and the resulting gravity fields are compared. The relative root mean square residuals between the fields calculated with this replacement are at most 5%.  相似文献   

Geomagnetic Reversals and Dynamo Bursts in a Simple Geodynamo Model     

E. V. Yushkov  D. D. Sokoloff 《Izvestiya Physics of the Solid Earth》2018,54(4):652-657

The question of what exactly happens with the geodynamo process during the reversal of a geomagnetic field is studied in a simple geodynamo model. The geodynamo action is described by the so called dynamo number characterizing the joint action of the main drivers of the geomagnetic field, i.e., the differential rotation and mirror–asymmetric convection. In mirror-asymmetric convection, for instance, in the northern hemisphere, there are more right vortices than left vortices, whereas in the southern hemisphere, there are more left vortices than right vortices. The effect of the magnetic field on the flow is described by the suppression of the mirror asymmetry: due to this suppression, e.g., in the northern hemisphere, the excess of right vortices over left vortices decreases. It is also assumed that due to this suppression, the mirror asymmetry can change its sign; i.e., the number of left vortices in the northern hemisphere can become larger than the number of right vortices. Correspondingly, the dynamo number can also change its sign. It is shown that the short-term changes of the sign of the dynamo number are responsible for the very short time span accommodating the reversal, when compared to the interval between the reversals.  相似文献   

High Latitude Magnetic Impulse Events (MIEs): Polarization Peculiarities and Excitation Conditions     

N. A. Kurazhkovskaya  B. I. Klain 《Izvestiya Physics of the Solid Earth》2018,54(5):698-711

Polarization characteristics (polarization type, ellipticity ε, tilt angle τ of the polarization ellipse’s major axis) of high-latitude magnetic impulse events (MIEs) observed at the latitude of the dayside polar cusp are studied. It is established that all impulses are elliptically polarized, being right-polarized in 43% of cases (R-type) and left-polarized in 57% of cases (L-type). The right-polarized MIEs on the ground are more pronounced in the azimuthal direction, whereas the left-polarized events are more clearly marked in the meridional direction. The MIEs of both polarization types have the properties of intermittent processes. It is shown that diurnal and seasonal variations in the occurrence frequency and amplitudes of the events depend significantly on the type of their polarization. The R- and L-type impulse events are predominantly observed during the descending and ascending phase of the solar cycle, respectively. Solar wind high-speed streams (HSSs) are more favorable for exciting right-polarized impulses, whereas left-polarized impulse events are more efficiently excited by coronal mass ejection (CME). It is established that R-type impulses emerge in the conditions when the orientation of the interplanetary magnetic field vector is close to the radial direction against the development of moderate magnetospheric substorms whereas the L-type impulses appear when IMF is perpendicular to the Sun–Earth line in the absence of substorms. The behavior of the characteristics of impulse events significantly depends on the value of the IMF Bz-component and on the angle θ_xB = arccos(Bx/B). It is conjectured that excitation of the two groups of impulses is caused by the IMF structures in the solar wind stream with the characteristic configuration in the ecliptic plane, which determine the polarization type and properties of MIEs.  相似文献