Spectral harmonic analysis and synthesis of Earth’s crust gravity field

We developed and applied a novel numerical scheme for a gravimetric forward modelling of the Earth’s crustal density structures based entirely on methods for a spherical analysis and synthesis of the gravitational field. This numerical scheme utilises expressions for the gravitational potentials and their radial derivatives generated by the homogeneous or laterally varying mass density layers with a variable height/depth and thickness given in terms of spherical harmonics. We used these expressions to compute globally the complete crust-corrected Earth’s gravity field and its contribution generated by the Earth’s crust. The gravimetric forward modelling of large known mass density structures within the Earth’s crust is realised by using global models of the Earth’s gravity field (EGM2008), topography/bathymetry (DTM2006.0), continental ice-thickness (ICE-5G), and crustal density structures (CRUST2.0). The crust-corrected gravity field is obtained after modelling and subtracting the gravitational contribution of the Earth’s crust from the EGM2008 gravity data. These refined gravity data mainly comprise information on the Moho interface and mantle lithosphere. Numerical results also reveal that the gravitational contribution of the Earth’s crust varies globally from 1,843 to 12,010 mGal. This gravitational signal is strongly correlated with the crustal thickness with its maxima in mountainous regions (Himalayas, Tibetan Plateau and Andes) with the presence of large isostatic compensation. The corresponding minima over the open oceans are due to the thin and heavier oceanic crust.     

Genetic relations between meteorites and terrestrial and lunar rocks

According to their genesis, meteorites are classified into heliocentric (which originate from the asteroid belt) and planetocentric (which are fragments of the satellites of giant planets, including the Proto-Earth). Heliocentric meteorites (chondrites and primitive meteorites genetically related to them) used in this study as a characteristic of initial phases of the origin of the terrestrial planets. Synthesis of information on planetocentric meteorites (achondrites and iron meteorites) provides the basis for a model for the genesis of the satellites of giant planets and the Moon. The origin and primary layering of the Earth was initially analogously to that of planets of the HH chondritic type, as follows from similarities between the Earth’s primary crust and mantle and the chondrules of Fe-richest chondrites. The development of the Earth’s mantle and crust precluded its explosive breakup during the transition from its protoplanetary to planetary evolutionary stage, whereas chondritic planets underwent explosive breakup into asteroids. Lunar silicate rocks are poorer in Fe than achondrites, and this is explained in the model for the genesis of the Moon by the separation of a small metallic core, which sometime (at 3–4 Ga) induced the planet’s magnetic field. Iron from this core was involved into the generation of lunar depressions (lunar maria) filled with Fe- and Ti-rich rocks. In contrast to the parent planets of achondrites, the Moon has a olivine mantle, and this fact predetermined the isotopically heavier oxygen isotopic composition of lunar rocks. This effect also predetermined the specifics of the Earth’s rocks, whose oxygen became systematically isotopically heavier from the Precambrian to Paleozoic and Mesozoic in the course of olivinization of the peridotite mantle, a processes that formed the so-called roots of continents.     

Extraction of the anomaly magnetic field of the earth from stratospheric balloon magnetic surveys at altitudes of 20–40 km

The solution to the problem of extraction of the anomaly Earth’s magnetic field (EMF) from stratospheric balloon magnetic surveys with the help of global analytical models of the normal EMF is proposed. In the problem solution, errors for the analytical models of the normal EMF and its secular variation at a set moment of time are assessed; the found error is introduced as a correction to the extracted anomaly EMF. The error of the model is determined in the places where significant magnetic anomalies are absent. In this case, the error of the model corresponds to deviations of the normal EMF components, synthesized by coefficients of analytical models, and to deviations of the EMF secular variations from the measured values at quite a low value of the variable EMF or one being taken into account. These places are determined when carrying out additional measurements in vertical gradients of the EMF with the use of scalar magnetometers at the gauge length of 6 km. It has been shown that the found places can be considered as nonanomaly, if the difference of values of the anomaly EMF at the gauge length of 6 km does not exceed 1.5 nT within the profile’s portion of about 100 km in length. An experiment in nature has revealed that errors for the IGRF-2005 and IGRF-2010 models, corrected for secular variation of the EMF, can reach 200 and 140 nT, respectively, within the limits of the territory where the Kama-Emba magnetic anomaly is located; these errors are determined by the considered causes. Comparison of aerostatic profiles of magnetic anomalies with data on the anomaly EMF, derived from the maps, has shown that the realizations derived from the maps contain overestimated negative values of the anomaly EMF, because they reflect processes in the near-surface layer of the Earth’s crust. This fact causes the situation when attempts to recalculate the anomaly EMF into the upper half-space by the near-surface data still have not been successful. Only realizations derived at the altitudes comparable to the thickness of the Earth’s crust can give an adequate model of the anomaly EMF in the circumterrestrial space and enable us to recalculate magnetic anomalies reliably into any altitude levels.     

Development of methods for constructing models for intra-year irregularity in the Earth’s rotation

The development of methods for the construction of stochastic, dynamical models for intra-year irregularity of the Earth’s rotation is considered. A correlational model based on harmonically additive and parametrically random, colored and broadband, gravitational-tidal perturbations from the Sun and Moon is developed. One-dimensional and multi-dimensional characteristic functions are found for the case of Gaussian and non-Gaussian colored and broadband fluctuations in the irregularity of the Earth’s rotation. Examples of computer modeling of the irregularity in the Earth’s rotation based on a priori and a posteriori IERS data are presented.     

Open magnetic fields on the Sun and solar wind parameters at the Earth’s orbit

It is shown that the parameters of the solar-wind magnetic field are determined by regions in coronal holes at distances of 1.1–1.4 solar radii, where the field lines are radial at low heights. Expanding further in a narrow nozzle or funnel, the field lines become radial throughout the unipolar region at 2.5 solar radii. Hence, the traditional approach of comparing the characteristics of the interplanetary field at the Earth’s orbit and at the corresponding helio-projection point on the Sun is not quite correct. It gives good results for the signs and sector structure of the field; however, the magnitude of the field is formed in a more extensive area. Taking this into account, we can correlate the field values on the Sun with the interplanetary magnetic field (IMF), and thus explain the absence of weak fields in the vicinity of the IMF neutral line (the two-peaked nature of the distribution).     

Stress state of the Earth’s crust of the Kuril Islands and Kamchatka before the Simushir earthquake

The field of modern tectonic stresses was reconstructed for the Earth’s crust of the northwestern segment of the Pacific subduction zones. For this purpose, we used the method of cataclastic analysis and data on the magnitude of the stresses released at the source of the Simushir earthquake of 2006, which allowed us to determine both the orientation of the principal stress axes and the magnitude of the stresses and to estimate the effective strength of rock masses. The effective cohesion was estimated for this region of the Earth’s crust as 12 bar, and the maximum shear stresses are no higher than 300 bar. The analysis of the reconstructed stress field in the zone of the preparation of the Simushir earthquake showed that this region was almost free of domains with high stresses where brittle failure requires considerable energy inputs. The medium level of effective pressure indicates that this region is most favorable for the development of a large-scale brittle failure.     

Effect of global factors on karst formation in Nizhegorodsky oblast

In studies of the dynamics of the activation of karst and suffosion processes in the karst-hazardous districts of Nizhegorodsky oblast, temporal-spectral and correlation analyses are carried out on multiyear time series data on the number of sinkholes in the town of Dzerzhinsk, fluctuations in the water level in the Oka River, fluctuations in solar activity, and variations in the speed of the Earth’s rotation. It is shown that the dynamics of the karst and suffosion processes is related to variations in the regional fluid dynamics, which are controlled, in turn, by fluctuations in solar activity and in the speed of the Earth’s rotation.     

Late Cenozoic geodynamics and mechanical coupling of crustal and upper mantle deformations in the Mongolia-Siberia mobile area

Comprehensive analysis of the parameters characterizing contemporary and neotectonic deformations of the Earth’s crust and upper mantle developed in the Mongolia-Siberia area is presented. The orientation of the axes of horizontal deformation in the geodetic network from the data of GPS geodesy is accepted as an indicator of current deformations at the Earth’s surface. At the level of the middle crust, this is the orientation of the principal axes of the stress-tensors calculated from the mechanisms of earthquake sources. The orientation of the axes of stress-tensors reconstructed on the basis of structural data is accepted as an indicator of Late Cenozoic deformations in the upper crust. Data on seismic anisotropy of the upper mantle derived from published sources on the results of splitting of shear waves from remote earthquakes serve as indicators of deformation in the mantle. It is shown that the direction of extension (minimum compression) in the studied region coincides with the direction of anisotropy of the upper mantle, the median value of which is 310–320° NW. Seismic anisotropy is interpreted as the ordered orientation of olivine crystals induced by strong deformation owing to the flow of mantle matter. The observed mechanical coupling of the crust and upper mantle of the Mongolia-Siberia mobile area shows that the lithospheric mantle participated in the formation of neotectonic structural elements and makes it possible to ascertain the main processes determining the Late Cenozoic tectogenesis in this territory. One of the main mechanisms driving neotectonic and contemporary deformations in the eastern part of the Mongolia-Siberia area is the long-living and large-scale flow of the upper mantle matter from the northwest to the southeast, which induces both the movement of the northern part of the continent as a whole and the divergence of North Eurasia and the Amur Plate with the formation of the Baikal Rift System. In the western part of the region, deformation of the lithosphere is related to collisional compression, while in the central part, it is due to the dynamic interaction of these two large-scale processes.     

Estimation of Vertical Continuous Stochastic Parameters from Seismic Reflection Data

This paper presents a scheme to invert reflected seismic wave fields for vertical spatial statistics of the Earth’s continuous stochastic velocity distribution. The forward model is based on a single scattering theory, where a seismogram is modeled as a convolution of a source wavelet and stochastic reflectivity, which obeys a von Kármán autocorrelation function. Tests with synthetic data indicate that the method presented here recovers vertical characteristic length from seismic reflection data that is similar to that of the original velocity model; however, the inversion does not reliably recover the Hurst exponent, ν. The input wavelet’s power spectrum is a free parameter in the inversion and is estimated as well, but is band-limited relative to the original source wavelet. Noise degrades the quality of the estimates of the stochastic parameters such that the recovered stochastic parameters are biased according to the power spectrum of the noise.     

On the local multiscale determination of the Earth’s disturbing potential from discrete deflections of the vertical

As a first approximation, the Earth is a sphere; as a second approximation, it may be considered an ellipsoid of revolution. The deviations of the actual Earth’s gravity field from the ellipsoidal “normal” field are so small that they can be understood to be linear. The splitting of the Earth’s gravity field into a “normal” and a remaining small “disturbing” field considerably simplifies the problem of its determination. Under the assumption of an ellipsoidal Earth model, high observational accuracy is achievable only if the deviation (deflection of the vertical) of the physical plumb line, to which measurements refer, from the ellipsoidal normal is not ignored. Hence, the determination of the disturbing potential from known deflections of the vertical is a central problem of physical geodesy. In this paper, we propose a new, well-promising method for modelling the disturbing potential locally from the deflections of the vertical. Essential tools are integral formulae on the sphere based on Green’s function with respect to the Beltrami operator. The determination of the disturbing potential from deflections of the vertical is formulated as a multiscale procedure involving scale-dependent regularized versions of the surface gradient of the Green function. The modelling process is based on a multiscale framework by use of locally supported surface curl-free vector wavelets.      

On Mathematical Aspects of a Combined Inversion of Gravity and Normal Mode Variations by a Spline Method

This paper provides a brief overview of two linear inverse problems concerned with the determination of the Earth’s interior: inverse gravimetry and normal mode tomography. Moreover, a vector spline method is proposed for a combined solution of both problems. This method uses localised basis functions, which are based on reproducing kernels, and is related to approaches which have been successfully applied to the inverse gravimetric problem and the seismic traveltime tomography separately.     

Fault-block structures in the eastern margin of the Amur lithospheric plate,their seismicity,and fluid regimes

The results of long-term studies of the neotectonic processes and related phenomena such as the Earth’s interior degassing, the fluid discharge, and the high seismicity in the zone of interaction between the Amur and Okhotsk lithospheric plates at the transition between the Verkhnii and Srednii Amur regions were used for defining the separate structural blocks with different geodynamics and analyzing their relations with the seismic events during the periods of high seismic activity and quiescence. The heliometric and atmochemical studies in the Zeya-Bureya basin revealed zones of high permeability. Long-term observations of the fluid dynamics at the Konstantinovka mineral water deposit demonstrate a correlation between the variations in the water-soluble helium contents and the changes in the stress-deformed state of the blocks located up to 200 km away from regime observation sites.     

Coupling of the Crustal and upper mantle deformations in the Mongolia-Siberian Mobile Area

The complex analysis of parameters characterizing the modern deformations of the Earth’s crust and upper mantle in the territory of the Mongolia-Siberian Area is made. Directions of principal tension axes of stress-tensors, calculated with the use of earthquake source mechanisms have been taken as parameters of modern deformations at the level of the middle crust; directions of axes of horizontal strains in the geodesic network by the GPS data have been taken as such parameters at the level of the Earth’s surface. The strain parameters for the mantle depths are the data on seismic anisotropy derived from the published sources about the results of studies on splitting of transversal waves from distant earthquakes. Seismic anisotropy is interpreted as the ordered orientation of olivine crystals, which appears with great strains resulting from the flow of the mantle material. It has been shown that directions of extensional strain axes (minimal compression) by geodesic and seismological data coincide with anisotropy directions in the upper mantle in the region whose median value is 310°–320°. The observed mechanical coupling of the crust and the upper mantle of the Mongolia-Siberian Mobile Area shows the participation of the lithospheric mantle in the formation of neotectonical structures and enables us to distinguish the principal processes determining the Late Cenozoic tectogenesis in this territory. One of the leading mechanisms for the neotectonical and modern deformations of the Mongolia-Siberian Region is the large-scale NW-SE material flow in the upper mantle causing both motion of the entire northern part of the continent and divergence of the Eurasia and the Amurian Plate. Lithospheric deformations in the western part of the region are related to collision-induced compression, while those in the central part are caused by interaction of these large-scale tectonic processes.     

Connection between variations of the stress-strain state of the Earth’s crust and seismic activity: The example of Southern California

A three-dimensional geomechanical model of Southern California, including mountain relief, fault tectonics, and characteristic internal borders, such as the roof of the consolidated crust and Moho surface, was created. The initial stress state of the model is determined by the gravitational force and horizontal tectonic movement, established on basis of GPS observations. Monitoring of variations in the stress state of the Earth’s crust and lithosphere, which are generated by seismic processes, has shown that the model enables us to predict an increase of seismic activity in a region and to mark the places in which average earthquakes can occur in the following two weeks.     

The paleomagnetic record from deep-sea sediment cores

The paleomagnetic record of deep-sea sediment cores is compared with that which would be expected from our knowledge of the Earth's magnetic field. It is found that some of the scatter in directions of magnetization obtained from deep-sea cores is removed in cores with very low sedimentation rate, the cause being that the secular variation of the Earth's magnetic field is more completely averaged out over the finite size of each sample, when these samples comprise a longer time span of sedimentation. Corrections have been applied to the results from a series of cores in order to obtain the inclination of the average direction of magnetization from the average inclination and the scatter of inclination. These corrected inclination values confirm the hypothesis that the average Earth's field over the past few million years has been similar to an axial dipole displaced towards the North Pole. The amount of displacement obtained was 168 km. The record of short-period polarity intervals within the Brunhes, the Matuyama and the Gauss epochs was studied. It was shown that these intervals are very scattered in position. It is thought that some hitherto undiscovered short-period polarity intervals may be responsible for part of the scatter, but it is also highly likely that many samples give spurious reversals (i.e., ones not caused by the Earth's magnetic field).The possible correlation between climatic changes and the Earth's magnetic field is examined. It is concluded that the cores which show correlations between direction and/or intensity of magnetization and climatic indicators, thus suggesting the possible correlation between climate and the Earth's magnetic field, are not accurately recording the relevant parameters of the Earth's magnetic field. The correlation must be caused by climatic effects which have a direct influence on the magnetization of the sediments.Very little is known about the mechanisms of magnetization in deep-sea sediment cores, and there are several unexplained phenomena, such as the fact that many cores have maximum susceptibilities which are vertical, and the fact that cores differ widely in their ability to record accurately the Earth's magnetic field.     

Observations of ultra-low-frequency geomagnetic disturbances reflecting the processes of the preparation and development of tsunamigenic earthquakes

Analysis of experimental observations of the Earth’s magnetic field variations recorded by the scientific instruments at the Northern Caucasus Geophysical Observatory of the Institute of Physics of the Earth, Russian Academy of Sciences, in the period 2007–2009 was performed. It was found that the characteristic ultra-low-frequency (ULF) waveforms of the geomagnetic disturbances were distinguished in the structure of the observed variations that reflect the process of preparation and development of a tsunamigenic earthquake.     

Composite detrital and thermal remanent magnetization in tuffs from Aeolian Islands (southern Tyrrhenian Sea) revealed by magnetic anisotropy

This paper reports on the complex relation between rock emplacement and remanence acquisition in tuffs deposited by pyroclastic density currents, disclosed by systematic measurements of the anisotropy of magnetic susceptibility and natural remanent magnetization (NRM). Thermal demagnetization shows that the NRM consists of two components with different blocking-temperature spectra. The direction of the low-temperature component is consistent with the geocentric axial dipole value, whereas the high-temperature component has dispersed directions. The magnetic fabric is oblate, the magnetic foliation is close to the bedding and the lineations are generally dispersed along a girdle within the foliation plane. The directions of the magnetic lineation and the high-temperature remanence component of individual specimens are close to each other. This correspondence suggests that the high blocking-temperature grains acquired a remanence aligned to their long dimension before deposition, while cooling within the explosive cloud and the moving pyroclastic current. Thereafter, during deposition, the traction processes at the base of the current oriented the grains along the flow direction and affected both fabric and high-temperature remanence. This NRM component results from mechanical orientation of previously magnetized grains and is thus detrital in origin. A second, thermal component was then acquired during the cooling of the low blocking-temperature grains after deposition. These results show that NRM in fine-grained pyroclastic rocks is affected by the Earth’s magnetic field as well as the emplacement processes and that magnetic fabric data are essential to unravel its complex nature.     

Some improved methods for modeling the Earth’s polar motion

Some improved methods for modeling the motions of the Earth’s pole determined by gravitational-tidal, fluctuating-dissipative perturbations occurring on various time scales are presented. The main attention is paid to dynamical linear-regression models and dynamical filtering models, which take into account dynamical measurement errors. Computer simulations of the oscillatory motion of the Earth’s pole for 1995–2010 are also presented.     

Geothermal field and distribution for earthquake source depths in the Baikal Rift Zone

A comparison between values of thermal flux and the deep temperatures calculated by them and the depths of earthquake sources in three areas of the Baikal Rift Zone is made. It has been shown that during transit from the Baikal depression to the adjacent mountain massif, the thermal flux decreases almost 2–3 times. The corresponding deep temperatures decrease to a similar degree. The available data for these areas on earthquake depths show that their lower boundary both beneath the depression and the massif is located at almost the same depth, which is about 20 km. In this paper, the conclusion is made that the cause of the absence of an interrelation between thermal and seismic fields lies in the discrepancy between the measured values of thermal flux and its deep values. This discrepancy arises because conductive heat transfer in the upper part of the Earth’s crust, up to 5–10 km depth, is highly distorted by heat-and-mass transfer of ground waters. In the middle part of the crust, the difference in temperatures beneath depressions and ridges is leveled horizontally, which is reflected in almost the same depth for the basement of the seismogenerating layer beneath these main rift structures.     

Simultaneous response of high-frequency geoacoustic emission and atmospheric electric field to strain of near-surface sedimentary rocks

During the period of October 1–18, 2009, 41 km southwest of Petropavlovsk-Kamchatsky, in the intersection zone of tectonic faults of various orders, simultaneous recording of the geoacoustic emission, gradient of the atmospheric electric field’s potential, strains of the Earth’s surface, atmospheric pressure, wind speed, and rain intensity was made. It was found for the first time that anomalous disturbances of high-frequency geoacoustic emission and atmospheric electric field near the Earth’s surface originate as a simultaneous response to extension of near-surface sedimentary rocks. In the case of compression, only disturbances of geoacoustic emission occur. Anomalies were recorded under quiet weather conditions and with rocks strains being two orders greater than those of tidal ones.