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1.
In geophysical studies investigating the lithosphere structure, the gravitational field generated by the ocean density contrast (i.e., bathymetry-generated gravitational field) represents a significant amount of the signal to be modelled and subsequently removed from the Earth’s gravity field. The ocean density contrast is typically calculated as the difference between the mean density values of the Earth’s crust and seawater. The approximation of the actual seawater density distribution by its mean value yields relative errors up to about 2% in computed quantities of the gravitational field. To reduce these errors, a more realistic model of the seawater density distribution is utilized based on the analysis of existing oceanographic data of salinity, temperature, and pressure (depth). We study the accuracy of the bathymetry-generated gravitational field quantities formulated for a depth-dependent model of the seawater density distribution. This density distribution approximates the seawater density variations due to an increasing pressure with depth, whereas smaller lateral density variations caused by salinity, temperature, and other oceanographic factors are not taken into consideration. The error analysis reveals that the approximation of the seawater density by the depth-dependent density model reduces the maximum errors to less than 0.6%. The corresponding depth-averaged errors are below 0.1%. The depth-dependent seawater density model is further facilitated in expressions for computing the bathymetry-generated gravitational field quantities by means of the spherical bathymetric (ocean bottom depth) functions. The numerical realization reveals large differences in the results obtained with and without consideration of the depth-dependent seawater density distribution. The maxima of absolute differences reach 201 m2/s2 and 16.5 mGal in computed values of the potential and attraction, respectively. The application of the depth-dependent seawater density model thus significantly improves the accuracy in the forward modelling of the bathymetric gravitational field quantities.  相似文献   

2.
During the General Assembly of the European Geosciences Union in April 2008, the new Earth Gravitational Model 2008 (EGM08) was released with fully-normalized coefficients in the spherical harmonic expansion of the Earth’s gravitational potential complete to degree and order 2159 (for selected degrees up to 2190). EGM08 was derived through combination of a satellite-based geopotential model and 5 arcmin mean ground gravity data. Spherical harmonic coefficients of the global height function, that describes the surface of the solid Earth with the same angular resolution as EGM08, became available at the same time. This global topographical model can be used for estimation of selected constituents of EGM08, namely the gravitational potentials of the Earth’s atmosphere, ocean water (fluid masses below the geoid) and topographical masses (solid masses above the geoid), which can be evaluated numerically through spherical harmonic expansions. The spectral properties of the respective potential coefficients are studied in terms of power spectra and their relation to the EGM08 potential coefficients is analyzed by using correlation coefficients. The power spectra of the topographical and sea water potentials exceed the power of the EGM08 potential over substantial parts of the considered spectrum indicating large effects of global isostasy. The correlation analysis reveals significant correlations of all three potentials with the EGM08 potential. The potential constituents (namely their functionals such as directional derivatives) can be used for a step known in geodesy and geophysics as the gravity field reduction or stripping. Removing from EGM08 known constituents will help to analyze the internal structure of the Earth (geophysics) as well as to derive the Earth’s gravitational field harmonic outside the geoid (geodesy).  相似文献   

3.
Besides generating seismic waves, which eventually dissipate, an earthquake also generates a static displacement field everywhere within the Earth. This global displacement field rearranges the Earth’s mass thereby causing the Earth’s rotation and gravitational field to change. The size of this change depends upon the magnitude, focal mechanism, and location of the earthquake. The Sumatran earthquake of December 26, 2004 is the largest earthquake to have occurred since the 1960 Chilean earthquake. Using a spherical, layered Earth model, the coseismic effect of the Sumatran earthquake upon the Earth’s length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are computed. Using a model of the earthquake source that is composed of five subevents having a total moment-magnitude M w of 9.3, it is found that this earthquake should have caused the length-of-day to decrease by 6.8 microseconds, the position of the Earth’s generalized figure axis to shift 2.32 milliarcseconds towards 127° E longitude, the Earth’s oblateness J 2 to decrease by 2.37 × 10−11 and the Earth’s pear-shapedness J 3 to decrease by 0.63 × 10−11. The predicted change in the length-of-day, position of the generalized figure axis, and J 3 are probably not detectable by current measurement systems. But the predicted change in oblateness is perhaps detectable if other effects, such as those of the atmosphere, oceans, and continental water storage, can be adequately removed from the observations.  相似文献   

4.
In this paper, the lithosphere is considered to be a homogeneous elastic spherical shell for the sake of simplicity and the stress equations for the base of the lithosphere are taken as boundary conditions. Then the stress equations are obtained for use in the computation of the stress field in the lithosphere with the satellite gravitational harmonic coefficients. The 5 × 5° global stress field in the lithosphere is computed from harmonics of 2–30°. The directions of principal stresses of this stress field agree favourably with the directions of principal stresses indicated by mid-plate earthquake mechanisms, in situ stress measurements and sensitive geological features. This result indicates that the drag forces exerted on the base of the lithosphere, due to gravitational mantle convection, may be among the driving forces of plate motion and a major source for the stress field in the lithosphere.  相似文献   

5.
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.  相似文献   

6.
This paper presents a wavelet analysis of temporal and spatial variations of the Earth’s gravitational potential based on tensor product wavelets. The time-space wavelet concept is realized by combining Legendre wavelets for the time domain and spherical wavelets for the space domain. In consequence, a multiresolution analysis for both temporal and spatial resolution is formulated within a unified concept. The method is then numerically realized by using first synthetically generated data and finally two real data sets.  相似文献   

7.
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.  相似文献   

8.
A new generation of global geopotential models (GGM) is being developed. These solutions offer a file with fully-normalized spherical harmonic coefficients of the Earth’s gravitational potential up to a degree greater than 2000 with very low commission errors. This paper analyses the recent Earth Gravitational Model EGM2008, developed up to degree and order 2159 with additional coefficients to degree 2190 and order 2159, which means recovering the gravitational field up to approximately 20 km wavelengths. 223 GPS/levelling points of the new Spanish High Precision Levelling Network in the Valencia region (Eastern Spain) are used as external tool for evaluation in that particular region. The same evaluation has been performed to other different global (EGM96 and EIGENCG03C), continental (EGG97), regional (IGG2005 and IBERGEO2006) and local (GCV07) geoid models for comparison purposes only. These comparisons show that EGM2008 is the geoid model that best fits to the GPS/levelling data in that region.  相似文献   

9.
The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes in the organic world.  相似文献   

10.
It has been indicated that the electric field that exists above the Earth’s surface contains information about the structure of underground inhomogeneities. Equations have been obtained and are used to illustrate the numerical calculations of the electric field strength along the Earth’s surface and some types of underground objects.  相似文献   

11.
Measurements of solar cosmic ray (SCR) protons in the magnetosphere can be used to verify models of the Earth’s magnetic field. The latitudinal profiles of precipitating SCRs with energies of 1–90 MeV were measured on the CORONAS-F low-orbiting satellite during a strong magnetic storm on October 29–30, 2003. A flux of precipitating protons can remain equal to the interplanetary flux only due to a strong pitch angle diffusion that originates when the radius of the field line curvature is close to that of the particle rotation Larmor radius. The observed boundaries of the strong diffusion region can be compared with the boundaries anticipated according to the models of the magnetic field of the Earth’s magnetosphere. The adiabaticity parameter values, calculated for several instants of the CORONAS-F satellite pass based on the TS05 and parabolic models, do not always correspond to measurements. How possible changes in the model configurations of the magnetic field can allow us to eliminate discrepancies with the experiment and to explain why solar protons with energies of several megaelectronvolts penetrate deep in the Earth’s inner magnetosphere is considered here.  相似文献   

12.
The present-day models of the Earth’s upper atmosphere make it possible to construct the spatial-temporal pattern of variations in the atmospheric parameters on the planetary scale in essence in the averaged form. The set of data on the satellite deceleration in the atmosphere, probe measurements aboard geophysical rockets, and radiowave incoherent scatter measurements in the Earth’s atmosphere are used to construct these standard models. The current level of the space studies makes it possible to use a new method to study the Earth’s upper atmosphere: to study the upper atmosphere by measuring the absorption of the solar XUV radiation by the Earth’s atmosphere during the solar disk observations.  相似文献   

13.
The effective elastic thickness of the lithosphere has an important role in constraining compositional structure, geothermal gradient and tectonic forces within the lithosphere and the thickness of this layer can be used to evaluate the earthquakes’ focal depth. Hence, assessment of the elastic thickness of the lithosphere by gravitational admittance method in Iran is the main objective of this paper. Although the global geopotential models estimated from the satellite missions and surface data can portray the Earth’s gravity field in high precision and resolution, there are some debates about using them for lithosphere investigations. We used both the terrestrial data which have been provided by NCC (National Cartographic Center of Iran) and BGI (Bureau Gravimetrique International), and the satellite-derived gravity and topography which are generated by EIGEN-GL04C and ETOPO5, respectively. Finally, it is concluded that signal content of the satellite-derived data is as rich as the terrestrial one and it can be used for the determination of the lithosphere bending.  相似文献   

14.
The results of long-term sounding of the lithosphere by seismic waves from the deep-focus Hindu Kush earthquakes are presented. The travel time series of the first longitudinal wave on a fixed base are constructed for six seismic observation stations (SS) located on the Russian Platform (the Obninsk SS), on the Siberian Platform (the Eltsovka SS), on the Cis-Ural Trough (the Arti SS), in the Central-Ural Megazone (the Sverdlovsk SS), in the Transbaikalia (the Bodaibo SS), and in the Northern Tien Shan (the Przhevalsk SS). The time series duration in years for these stations ranged from 1964–1970 to 2007. The travel time series of seismic waves for the stations indicated are characterized by multi-slope negative linear trends caused by changes in the stress-strain state of rocks. From the comparison of the trend slopes at different stations it follows that the changes in the stress conditions within the lithosphere are relatively weak in the aseismic regions of the Russian and Siberian Platforms and in the Ural Megazone, whereas in the seismically active regions of Tien Shan, Transbaikalia and the Cis-Ural Trough they are more pronounced. The correlation has been observed between the time series trends of the average annual travel times of seismic waves and the time series of the Earth’s rotation speed. The strongest correlation between the series can be seen for the stations, located on the platforms with weak manifestations of both seismicity and active geodynamic processes. Within the long-term periods of deceleration and acceleration of the Earth’s rotation, travel times of seismic waves are decreased and increased, respectively.  相似文献   

15.
The spatial distributions of electric fields and currents in the Earth’s atmosphere are calculated. Electric potential distributions typical of substorms and quiet geomagnetic conditions are specified in the ionosphere. The Earth is treated as a perfect conductor. The atmosphere is considered as a spherical layer with a given height dependence of electrical conductivity. With the chosen conductivity model and an ionospheric potential of 300 kV with respect to the Earth, the electric field near the ground is vertical and reaches 110 Vm−1. With the 60-kV potential difference in the polar cap of the ionosphere, the electric field disturbances with a vertical component of up to 13 V m−1 can occur in the atmosphere. These disturbances are maximal near the ground. If the horizontal scales of field nonuniformity are over 100 km, the vertical component of the electric field near the ground can be calculated with the one-dimensional model. The field and current distributions in the upper atmosphere can be obtained only from the three-dimensional model. The numerical method for solving electrical conductivity problems makes it possible to take into account conductivity inhomogeneities and the ground relief.  相似文献   

16.
The Earth’s crossings of the magnetic sector boundaries are accompanied by changes in the magnetosphere, ionosphere, and troposphere. We considered the baric field’s response to the crossing of the inter-planetary magnetic field (IMF) sector boundaries during a geomagnetically quiet period. The IMF sign is shown to affect atmospheric pressure in high-latitude regions. The efficiency and sign of the relationship vary during the year. The baric field response to the Earth’s crossing of the IMF sector boundaries is most distinct during equinoxes. It is shown that, during a geomagnetically quiet period, the circulation processes in the atmosphere drive the changes in the atmospheric pressure when the Earth passes from one IMF sector into another.  相似文献   

17.
The elasto-gravitational deformation response of the Earth’s solid parts to the perturbations of the pressure and gravity on the core-mantle boundary (CMB) and the solid inner core boundary (ICB), due to the dynamical behaviors of the fluid outer core (FOC), is discussed. The internal load Love numbers, which are formulized in a general form in this study, are employed to describe the Earth’s deformation. The preliminary reference Earth model (PREM) is used as an example to calculate the internal load Love numbers on the Earth’s surface, CMB and ICB, respectively. The characteristics of the Earth’s deformation variation with the depth and the perturbation periods on the boundaries of the FOC are also investigated. The numerical results indicate that the internal load Love numbers decrease quickly with the increasing degree of the spherical harmonics of the displacement and depend strongly on the perturbation frequencies, especially on the high frequencies. The results, obtained in this work, can be used to construct the boundary conditions for the core dynamics of the long-period oscillations of the Earth’s fluid outer core. Foundation item: State Natural Science Foundation of China (40174022 and 49925411) and the Projects from Chinese Academy of Sciences (KZCX2-106 and KZ952-J1-411).  相似文献   

18.
    
Based on the time series of observational variations of the length of day (LOD) and seismic data in the world, the relations of the decadal fluctuation and seasonal variation in the Earth’s rotation with global seismic activity are studied in this paper. The results suggest that there are overall correlations on temporal scale and regional discrepancy on spatial scale between global seismic activity and the Earth’s variable rotation, especially the seismic activity in the Eurasian seismic zone (not including southeast Asia) and the Lower California-Eastern Alaska seismic zone correlating well with the Earth’s variable rotation. According to the relations mentioned above, the observational data of the Earth’s rotation might provide a referential basis for monitoring global seismic activity. This project is sponsored by the National Key Basic Research Project and the National Natural Science Foundation of China. The English version is improved by Prof. Xin-Ling QIN, Institute of Geophysics, SSB, China.  相似文献   

19.
We have analyzed the regularities in the spatiotemporal behavior of the methane concentration and mass, recorded in different regions of the globe. In the southern hemisphere (SH), the methane concentration does not depend on latitude. In the northern hemisphere (NH), the methane concentration increases towards the Arctic zone. The maximum CH4 concentration in the fall is due to the action of the additional methane sources in the NH Arctic region. The methane flux calculations showed that in the SH the methane flux into the Earth’s atmosphere is barely season dependent. In the NH during the fall season, the methane flux considerably increases, and the difference between the maximum flux in August-September and the flux in December-January reaches three. The additional, still disregarded sources, sustaining high methane emission in the spring season at high SH latitudes are estimated to be as strong as 100–120 Tg per year. To equilibrate the methane supply to the atmosphere and methane sink in SH, additional, yet unidentified sources of over 300 Tg/yr are required. The global methane flux into the Earth’s atmosphere should be no less than 1050–1100 Tg yearly.  相似文献   

20.
The work is dedicated to investigation of Hot Flow Anomaly (HFA), formed at the front of Earth’s bows hock. Using Interball-Tail data we estimated orientation of the current sheet that was a cause of the anomaly. From the ion energy-time spectrogram we divided the anomaly into several regions. The motional electric fields near the HFA were estimated with 3D model of Earth’s bow shock. In accordance with previous investigations of HFA’s formation conditions these fields were directed towards the current sheet on both sides of it. We also provided the picture of HFA’s motion along the bow shock and calculated its speed. Analyzing ions’ bulk velocities within the HFA we found that the anomaly is expanding. This conclusion was supported by estimation of thermal and magnetic pressure balance. Ion energy-time spectrogram shows that anomaly is a complicated structure consisting of two parts—leading and trailing. Comparison of ion velocity distributions, magnetic field data and ion energy-time spectrogram provides better understanding of the phenomena and indicated the region that is the source of thermal and convective energy inside HFA.  相似文献   

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