Forward Modeling of Gravity, Gravity Gradients, and Magnetic Anomalies due to Complex Bodies

On the basis of the results of improved analytical expression of computation of gravity anomalies due to a homogeneous polyhedral body composed of polygonal facets, and applying the forward theory with the coordinate transformation of vectors and tensors, we deduced both the analytical expressions for gravity gradient tensors and for magnetic anomalies of a polygon, and obtained new analytical expressions for computing vertical gradients of gravity anomalies and vertical component of magnetic anomalies caused by a polyhedral body. And also we developed explicitly the complete unified expressions for the calculation of gravity anomalies, gravity gradient, and magnetic anomalies due to the homogeneous polyhedron. Furthermore, we deduced new analytical expressions for computing vertical gradients of gravity anomalies due to a finite rectangular prism by applying the newly obtained expressions for gravity gradient tensors due to a polyhedral target body. Comparison with forward calculation of models shows the correctness of these new expressions. It will reduce forward calculation time of gravity-magnetic anomalies and improve computational efficiency by applying our unified expressions for joint forward modeling of gravity-magnetic anomalies due to homogeneous polyhedral bodies.     

Mechanical Nature of Gravity and Tectonic Forces

There are two models of ultrahigh pressure metamorphism (UHPM) zone in Dabie: the model of under thrusting-returning which even arrives at the mantle and the superimposed model of tectonics in the crust. There are two points of view in the argument about formation depth of ultrahigh pressure metamorphism: (1) the depth can be calculated by hydrostatic equation; (2) the high pressure was composed of gravity, tectonic and other forces instead of merely gravity force. Some misunderstandings of mechanical conceptions presented in the paper showing the hydrostatic viewpoints should be open to question. The main conceptions are: (1) the confining pressure was only formed by gravity, and the differential stress was only formed by tectonic force; (2) the differential stress is not big enough to lead to form ultrahigh pressure metamorphism; (3) once tectonic overpressure goes beyond the limited strength of rocks the tectonic force would disappear and the rocks would be broken or rheomorphied at the same time. A short discussion in basic mechanics is made in this paper for a perfect process for discussing the argument.     

Minimally Modified Gravity Fitting Planck Data Better Than ΛCDM

Astronomy Reports - Here we present cosmology of a class of Minimally Modified Gravity theory dubbed as $$f(\mathcal{H})$$ theory. After introducing a concrete model for the free function, we find...     

Relativistic Models for Strange Stars in Massive Brans–Dicke Gravity

Astronomy Reports - In this paper, we examine the salient features of anisotropic quark stellar model in the background of massive Brans–Dicke gravity. We use the MIT bag model along with...     

Magnetic and Gravity Investigations of Lisan Peninsula-Dead Sea(Jordan)

The Lisan Peninsula is located within the Dead Sea basin which represents the plate boundary between African and Arabian plates. This basin constitutes a good example of a pull-apart basin because of its large dimensions, its structural simplicity and its active subsidence . The gravity data reveal that the Dead Sea basin can be divided into segments, each of them about 30 km long in N-S direction , where the Lisan Peninsula represents the deepest one (9 km thick Pleistocene sediments ), overlying about 6 km thick Mesozoic sediments . In addition , 20 km of extension was predicted along the Dead Sea basin, which indicates that the Dead Sea basin should be about 3.3 Ma in age . Furthermore, the Precambrian basement under the Lisan area is characterized by high susceptibility contrast that is related to continuous tectonic activity in the region.     

Gravity Investigation in Area East of River Nile （Khartoum State）

The purpose of the study is to investigate the subsurface geology of the area. For quantitative interpretation of the resulting Bouguer anomalies, borehole data are explored. This is done along several profiles obtained from software program G.model @ version 2.2 No.175. This program is base don two -dimensional mass distribution. The interpretation reveals two basinal features filling depressions in the basement complex named as Abu Harira basin and Kabbashi basin. They are structurally related to Khartourn basin. As a result, a geological/structural map of the area in east of the Nile is produced. The basinal features in the study area are considered as parts of the central Sudan (Khartourn basin) that had been subjected to several tectonic events that resulted in the formation of several fracture systems associated with block subsidence and formation of these basins.     

Optimal Interpolation of Gravity Maps Using a Modified Neural Network

This paper proposes an interpolation method based on a modified Kohonen artificial neural network, and is used to interpolate marine gravity data on a regular grid. This method combines accuracy comparable to that of kriging with a much shorter computing time than kriging. It is particularly efficient when both the size of the grid and the quantity of available data are large. Under some hypotheses similar to those of kriging with a trend, the unbiasedness and optimality of the method can be demonstrated. Comparison with kriging with a trend using marine gravity data shows similar results. Although neural interpolation is slightly less efficient, it is more robust outside of the marine data area.     

Glacigenic Characteristics of the Luoquan Formation and Sediment Gravity Flow Reworking on It

The origin of the Luoquan Formation which occurs along the southern margin of the North China Blockhas long been argued. Based on recent work. the Formation is considered as a glacial sedimentary sequencepartially reworked by sediment gravity flow. The major evidence for the glacigene of Luoquan Formationdiamictites is as follows: 1, a striated and polished pavement with various features resulting from glacialabrasion and plucking, such as crescentic gouge, crescentic fracture, streamlined form and glaciated step; 2.unsorted diamictites with striated clast. faceted clast and iron-shaped stone formed by glaciation; 3. rhythmitewith dropstones; 4. a glacial sedimentary sequence bearing advance-retreat cycles; and 5. wide distribution ofthe diamictites. Glacial deposits can be distinguished from sediment gravity flow deposits by the features men-tioned above. Some characteristics of sediment gravity flow existing in the Luoquan Formation diamictites in-dicate that glacial deposits might have been partially reworked by sediment gravity flow. Therefore, this papersuggests that the Luoquan Formation diamictite is a result of a glacial event rather than a mud flow deposit.The primary tillites are the principal contribution of the Luoquan Formation, while sediment gravity flow de-posits are the redeposited diamictites and should be termed as glacigenic sediment gravity flow deposits.     

Sandbox Experimental Study on the Influence of Rock Strength and Gravity on Formation of Thrusts

INTRODUCTIONRock deformation is normally explained by tec-tonic stress as rock deformation results fromthe tec-tonic stress field. The classic tools that explainedfracture mechanisms were the Coulomb shear fracturerule and the Anderson mode derived fromit (Zhu,1999) . More and more studies have shown that it isdifficult to explain rock deformation in a large strainrange using only the Coulomb shear fracture rule( Waltham,2002 ; Gutscher et al .,2001 ; Tikoff andWojtal ,1999) . As a ver…     

Anisotropic Scaling Models of Rock Density and the Earth’s Surface Gravity Field

In this paper we consider an anisotropic scaling approach to understanding rock density and surface gravity which naturally accounts for wide range variability and anomalies at all scales. This approach is empirically justified by the growing body of evidence that geophysical fields including topography and density are scaling over wide range ranges. Theoretically it is justified, since scale invariance is a (geo)dynamical symmetry principle which is expected to hold in the absence of symmetry breaking mechanisms. Unfortunately, to date most scaling approaches have been self-similar, i.e., they have assumed not only scale invariant but also isotropic dynamics. In contrast, most nonscaling approaches recognize the anisotropy (e.g., the strata), but implicitly assume that the latter is independent of scale. In this paper, we argue that the dynamics are scaling but highly anisotropic, i.e., with scale dependent differential anisotropy. By using empirical density statistics in the crust and a statistical theory of high Prandtl number convection in the mantle, we argue that is a reasonable model for the 3-D spectrum (K is the horizontal wavevector and K is its modulus, k _z is a vertical wavenumber), (s,H _z ) are fundamental exponents which we estimate as (5.3,3), (3,3) in the crust and mantle, respectively. We theoretically derive expressions for the corresponding surface gravity spectrum. For scales smaller than ≈100 km, the anisotropic crust model of the density (with flat top and bottom) using empirically determined vertical and horizontal density spectra is sufficient to explain the (Bouguer) g _z spectra. However, the crust thickness is highly variable and the crust-mantle density contrast is very large. By considering isostatic equilibrium, and using global gravity and topography data, we show that this thickness variability is the dominant contribution to the surface g _z spectrum over the range ≈100–1000 km. Using estimates of mantle properties (viscosity, thermal conductivity, thermal expansion coefficient, etc.), we show that the mantle contribution to the mean spectrum is strongest at ≈1000 km and is comparable to the variable crust thickness contribution. Overall, we produce a model which is compatible with both the observed (horizontal and vertical) density heterogeneity and surface gravity anomaly statistics over a range of meters to several thousand kilometers.     

Study on the Gravity Field and Deep-Seated Crustal Structure at the North Margin of the Qinghai-Tibet Plateau

1.I~ductionThenorthernmarginoftheQinghai-TibetplateauincludestheAltllnMis.,theQilianMis.,KunlunMis.,theQaidambasinandthesouthernTarimbasin.ThisareaistCctonicallycharacterizedbyintensiveCenozoicdeformationwithcomplicateddeformationalmechedsm(Molnaretal.,1987;Zheng,1991;Culetal.,1994;Ding,1995andXuetal.,1996).Thedeformationalmechanismsincludethrust-napping,strike-slipping,extensionandblockrotation,aswellassimultaneousupliftingandtypicalbasin-rangetectonics(CulandXu,1996).IntermsofCenozoi…     

A Study of Iron Deposits in the Jining Area based on Correlation Analysis Gravity and Magnetic Anomalies

Please?refer?to?the?attachment(s)?for?more?details.     

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.     

Gravity anomalies,flexure, and deformation of the converging Indian lithosphere in Nepal and Sikkim–Darjeeling Himalayas

Researchers ubiquitously noted that the common processes of partitioning oblique convergence in response to drag from the trench-hanging plate simultaneously produce radial slips, along-strike translation, and extension parallel to the deformation front. Here, we focus on the area between Nepal and Sikkim–Darjeeling Himalayas, and carry out gravity and finite-element stress modeling of the strike-orthogonal converging Indian lithosphere. We delineate the geometries of different layers and their interfaces through gravity modeling. The optimum model parameters along with rheological parameters of different layers are used for finite-element modeling. Finite-element modeling is done with boundary conditions of keeping the upper surface free and rigidly fixing the section of the northern boundary below the Main Himalayan Thrust. We impart on its frontal section an amount of 6 × 10¹² N/m force, equivalent to resistive force of the Himalayan–Tibet system, and analyze the maximum and minimum compressive stress fields evolved in the lithosphere. We testify our observations with earthquake database and other geophysical and geological studies. We note that an increasing flexing of the Indian lithosphere beyond the Main Boundary Thrust becomes maxima between the Main Central Thrust and South Tibetan Detachment in both the areas; however, more steepening of the Moho boundary is identified in the Sikkim–Darjeeling Himalaya. This abrupt change in lithospheric geometry beneath the Greater Himalaya is likely correlated with the sharp elevation changes in the topography. Although the highest seismicity concentration is dominant in this zone, the Lesser and the Tethys Himalayas in Sikkim–Darjeeling area also record relatively fair seismic activity. More compressive stress field in different layers right within the sharp bending zone supports this observation. We thus propose that the sharp bending zone beneath the Greater Himalaya is suffering maximum deformation, and the deformation is continued in the mantle too. We also identify both right-lateral shear and radial vergence slip, which are presumably associated with the general dynamics and kinematics of the Himalaya.     

Density section of the Earth’s crust in the Deryugin Basin (Sea of Okhotsk): Gravity modeling results

A geological density section of the Deryugin Basin (western part of the Sea of Okhotsk) was studied along the profile Sakhalin Island-Deryugin Basin-Central Okhotsk Rise. The investigations were conducted by the method of gravity modeling, which allowed us to trace the density variations of the Earth’s crust layers along the lateral. The horizontal density stratification of the Earth’s crust layers was found, which assumes a stratified-block model of its structure. The established density structure of the Earth’s crust showed that the Deryugin Basin is located in the junction zone between the Sakhalin-Hokkaido microplate and the Okhotsk Sea Plate separated by a structural suture. The western and eastern edges of the basin belong to the aforementioned plates, respectively. It was assumed that accumulations of various mineral associations are confined to the suture zone, while the “granite” layer (basement) of the Deryugin trough walls in the western edge of the Deryugin Basin presumably contains secondary reservoirs of hydrocarbons.     

Tectono-Magmatism of Two Phases and Deposit Enrichment Regularity in Gejiu Tin Polymetallic Ore-Field, Yunnan, China: Evidences from Geochronology,Geochemistry, Gravity and Paleomagnetism

Please refer to the attachment(s) for more details.     

Gravity anomalies over the Central Indian Ridge between 3<Superscript>∘</Superscript>S and 11<Superscript>∘</Superscript>S,Indian Ocean: Segmentation and crustal structure

High-resolution shipboard geophysical investigations along the Indian Ocean ridge system are sparse especially over the Carlsberg and Central Indian ridges. In the present study, the shipboard gravity and multibeam bathymetry data acquired over a 750 km long section of the Central Indian Ridge between 3 ^°S and 11 ^°S have been analysed to understand the crustal structure and the ridge segmentation pattern. The mantle Bouguer anomalies (MBA) and the residual mantle Bouguer anomalies (RMBA) computed in the study area have shown significant variations along the ridge segments that are separated by transform and non-transform discontinuities. The MBA lows observed over the linear ridge segments bounded by well-defined transform faults are attributed to the thickening of the crust at the middle portions of the ridge segments. The estimates of crustal thickness from the RMBA shows an average of 5.2 km thick crust in the axial part of the ridge segments. The MBA and relative RMBA highs along the two non-transform discontinuities suggests a thinner crust of up to 4.0 km. The most significant MBA and RMBA highs were observed over the Vema transform fault suggesting thin crust of 4 km in the deepest part of the transform fault where bathymetry is more than 6000 m. The identified megamullion structures have relative MBA highs suggesting thinner crust. Besides MBA lows along the ridge axis, significant off-axis MBA lows have been noticed, suggesting off-axis mantle upwelling zones indicative of thickening of the crust. The rift valley morphology varies from the typical V-shaped valley to the shallow valley floor with undulations on the inner valley floor. Segments with shallow rift valley floor have depicted well-defined circular MBA lows with persistent RMBA low, suggesting modulation of the valley floor morphology due to the variations in crustal thickness and the mantle temperature. These are supported by thicker crust and weaker lithospheric mantle.