The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Lars E Sjoberg - One of the best experts on this subject based on the ideXlab platform.
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On the isostatic Gravity Anomaly and disturbance and their applications to Vening Meinesz–Moritz gravimetric inverse problem
Geophysical Journal International, 2013Co-Authors: Lars E SjobergAbstract:In this study,we showthat the traditionally defined Bouguer Gravity Anomaly needs a correction to become 'the no-topography Gravity Anomaly' and that the isostatic Gravity Anomaly is better defined by the latter Anomaly plus a Gravity Anomaly compensation effect than by the Bouguer Gravity Anomaly plus a gravitational compensation effect. This is because only the newisostatic Gravity Anomaly completely removes and compensates for the topographic effect. F. A. Vening Meinesz' inverse problem in isostasy deals with solving for the Moho depth from the known external Gravity field and mean Moho depth (known, e.g. from seismic reflection data) by a regional isostatic compensation using a flat Earth approximation. H. Moritz generalized the problem to that of a global compensation with a spherical mean Earth approximation. The problem can be formulated mathematically as that of solving a non-linear Fredholm integral equation. The solutions to these problems are based on the condition of isostatic balance of the isostatic Gravity Anomaly, and, theoretically, this assumption cannot be met by the old definition of the isostatic Gravity Anomaly. We show how the Moho geometry can be solved for the Gravity Anomaly, Gravity disturbance and disturbing potential, etc., and, from a theoretical point of view, all these solutions are the same.
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on the isostatic Gravity Anomaly and disturbance and their applications to vening meinesz moritz gravimetric inverse problem
Geophysical Journal International, 2013Co-Authors: Lars E SjobergAbstract:In this study,we showthat the traditionally defined Bouguer Gravity Anomaly needs a correction to become 'the no-topography Gravity Anomaly' and that the isostatic Gravity Anomaly is better defined by the latter Anomaly plus a Gravity Anomaly compensation effect than by the Bouguer Gravity Anomaly plus a gravitational compensation effect. This is because only the newisostatic Gravity Anomaly completely removes and compensates for the topographic effect. F. A. Vening Meinesz' inverse problem in isostasy deals with solving for the Moho depth from the known external Gravity field and mean Moho depth (known, e.g. from seismic reflection data) by a regional isostatic compensation using a flat Earth approximation. H. Moritz generalized the problem to that of a global compensation with a spherical mean Earth approximation. The problem can be formulated mathematically as that of solving a non-linear Fredholm integral equation. The solutions to these problems are based on the condition of isostatic balance of the isostatic Gravity Anomaly, and, theoretically, this assumption cannot be met by the old definition of the isostatic Gravity Anomaly. We show how the Moho geometry can be solved for the Gravity Anomaly, Gravity disturbance and disturbing potential, etc., and, from a theoretical point of view, all these solutions are the same.
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determination of Gravity Anomaly at sea level from inversion of satellite Gravity gradiometric data
Journal of Geodynamics, 2011Co-Authors: M. Eshagh, Lars E SjobergAbstract:Abstract Gravity gradients can be used to determine the local Gravity field of the Earth. This paper investigates downward continuation of all elements of the disturbing gravitational tensor at satellite level using the second-order partial derivatives of the extended Stokes formula in the local-north oriented frame to determine the Gravity Anomaly at sea level. It considers the inversion of each gradient separately as well as their joint inversion. Numerical studies show that the gradients T zz , T xx , T yy and T xz have similar capability of being continued downward to sea level in the presence of white noise, while the gradient T yz is considerably worse than the others. The bias-corrected joint inversion process shows the possibility of recovering the Gravity Anomaly with 1 mGal accuracy. Variance component estimation is also tested to update the observation weights in the joint inversion.
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new views of the spherical bouguer Gravity Anomaly
Geophysical Journal International, 2004Co-Authors: Petr Vaníček, Zdeněk Martinec, Robert Tenzer, Lars E Sjoberg, Will FeatherstoneAbstract:SUMMARY This paper presents a number of new concepts concerning the Gravity Anomaly. First, it identifies a distinct difference between a surface (2-D) Gravity Anomaly (the difference between actual Gravity on one surface and normal Gravity on another surface) and a solid (3-D) Gravity Anomaly defined in the fundamental gravimetric equation. Second, it introduces the ‘no topography’ Gravity Anomaly (which turns out to be the complete spherical Bouguer Anomaly) as a means to generate a quantity that is smooth, thus suitable for gridding, and harmonic, thus suitable for downward continuation. It is understood that the possibility of downward continuing a smooth Gravity Anomaly would simplify the task of computing an accurate geoid. It is also shown that the planar Bouguer Anomaly is not harmonic, and thus cannot be downward continued.
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the effect of downward continuation of Gravity Anomaly to sea level in stokes formula
Journal of Geodesy, 2001Co-Authors: Lars E SjobergAbstract:Stokes' well-known formula integrates Gravity anomalies on a sphere to geoidal undulations. Traditionally the effect of continuing the observed Gravity Anomaly from the Earth's surface to sea level is estimated in a rather rough manner, which significantly degrades the resulting geoidal undulations. In addition, the derived fictitious Gravity anomalies at sea level are numerically unstable. This problem is solved by directly deriving a surface integral for the effects on the geoidal undulation and height Anomaly. In addition, the solution is stabilized by optimized spectral smoothing by minimizing the mean square error. The final formula is a function of the Gravity Anomaly, height Anomaly and topographic height.
Yuanman Zheng - One of the best experts on this subject based on the ideXlab platform.
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preferential filtering for Gravity Anomaly separation
Computers & Geosciences, 2013Co-Authors: Lianghui Guo, Xiaohong Meng, Zhaoxi Chen, Yuanman ZhengAbstract:We present the preferential filtering method for Gravity Anomaly separation based on Green equivalent-layer concept and Wiener filter. Compared to the conventional upward continuation and the preferential continuation, the preferential filtering method has the advantage of no requirement of continuation height. The method was tested both on the synthetic Gravity data of a model of multiple rectangular prisms and on the real Gravity data from a magnetite area in Jilin Province, China. The results show that the preferential filtering method produced better separation of Gravity Anomaly than both the conventional low-pass filtering and the upward continuation.
Jayanta Madhab Borgohain - One of the best experts on this subject based on the ideXlab platform.
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seismic b values and its correlation with seismic moment and bouguer Gravity Anomaly over indo burma ranges of northeast india tectonic implications
Tectonophysics, 2018Co-Authors: Dipok K Bora, Kajaljyoti Borah, Rinku Mahanta, Jayanta Madhab BorgohainAbstract:Abstract b-value is one of the most significant seismic parameters for describing the seismicity of a given region at a definite time window. In this study, high-resolution map of the Gutenberg-Richter b-value, seismic moment-release, Bouguer Gravity Anomaly and fault-plane solutions containing faulting styles are analyzed in the Indo-Burma ranges of northeast India using the unified and homogeneous part of the seismicity record in the region (January 1964–December 2016). The study region is subdivided into few square grids of geographical window size 1° × 1° and b-values are calculated in each square grid. Our goal is to explore the spatial correlations and anomalous patterns between the b-value and parameters like seismic moment release, Bouguer Gravity Anomaly and faulting styles that can help us to better understand the seismotectonics and the state of present-day crustal stress within the Indo-Burma region. Most of the areas show an inverse correlation between b-value and seismic moment release as well as convergence rates. While estimating the b-value as a function of depth, a sudden increase of b-value at a depth of 50–60 km was found out and the receiver function modeling confirms that this depth corresponds to the crust-mantle transition beneath the study region. The region is also associated with negative Bouguer Gravity anomalies and an inverse relation is found between Gravity Anomaly and b-value. Comparing b-values with different faulting styles, reveal that the areas containing low b-values show thrust mechanism, while the areas associated with intermediate b-values show strike-slip mechanism. Those areas, where the events show thrust mechanism but containing a strike-slip component has the highest b-value.
Yan Ming Wang - One of the best experts on this subject based on the ideXlab platform.
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gsfc00 mean sea surface Gravity Anomaly and vertical Gravity gradient from satellite altimeter data
Journal of Geophysical Research, 2001Co-Authors: Yan Ming WangAbstract:A mean sea surface, GSFC00, and its derivatives, the altimetry Gravity Anomaly and vertical Gravity gradient fields, were computed using sea surface heights of TOPEX, ERS, and Geosat satellite altimeter missions provided by the NASA Ocean Altimeter Pathfinder Project [Koblinsky et al., 1998]. A new estimation method, distinct from the GSFC98 mean sea surface computation [Wang, 2000a], was explored and used to reduce ocean variability in the mean sea surface heights. The Gravity Anomaly and vertical Gravity gradient fields were then computed from the mean sea surface height implied geoid undulations. Validation of the GSFC00 mean sea surface and Gravity Anomaly was also performed.
Partha Pratim Chakraborty - One of the best experts on this subject based on the ideXlab platform.
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the seismic b value and its correlation with bouguer Gravity Anomaly over the shillong plateau area tectonic implications
Journal of Asian Earth Sciences, 2007Co-Authors: P K Khan, Partha Pratim ChakrabortyAbstract:Abstract Clues to the understanding of intra- and inter-plate variations in strength or stress state of the crust can be achieved through different lines of evidence and their mutual relationships. Among these parameters Bouguer Gravity anomalies and seismic b-values have been widely accepted over several decades for evaluating the crustal character and stress regime. The present study attempts a multivariate analysis for the Shillong Plateau using the Bouguer Gravity Anomaly and the earthquake database, and establishes a causal relationship between these parameters. Four seismic zones (Zones I–IV), with widely varying b-values, are delineated and an excellent correlation between the seismic b-value and the Bouguer Gravity Anomaly has been established for the plateau. Low b-values characterize the southwestern part (Zone IV) and a zone (Zone III) of intermediate b-values separates the eastern and western parts of the plateau (Zones I and II) which have high b-values. Positive Bouguer Anomaly values as high as +40 mgal, a steep gradient in the Bouguer Anomaly map and low b-values in the southwestern part of the plateau are interpreted as indicating a thinner crustal root, uplifted Moho and higher concentration of stress. In comparison, the negative Bouguer Anomaly values, flat regional gradient in the Bouguer Anomaly map and intermediate to high b-values in the northern part of the plateau are consistent with a comparatively thicker crustal root and lower concentration of stress, with intermittent dissipation of energy through earthquake shocks. Further, depth wise variation in the b-value for different seismic zones, delineated under this study, allowed an appreciation of intra-plateau variation in crustal thickness from ∼30 km in its southern part to ∼38 km in the northern part. The high b-values associated with the depth, coinciding with lower crust, indicate that the Shillong Plateau is supported by a strong lithosphere.
