| 1. |
- Bagherbandi, Mohammad, et al.
(författare)
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Comparative analysis of Vening-Meinesz Moritz isostatic models using the constant and variable crust-mantle density contrast - a case study of Zealandia
- 2013
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Ingår i: Journal of Earth System Science. - : Springer Science and Business Media LLC. - 0973-774X .- 0253-4126. ; 122:2, s. 339-348
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Tidskriftsartikel (refereegranskat)abstract
- We compare three different numerical schemes of treating the Moho density contrast in gravimetric inverse problems for finding the Moho depths. The results are validated using the global crustal model CRUST2.0, which is determined based purely on seismic data. Firstly, the gravimetric recovery of the Moho depths is realized by solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy while the constant Moho density contrast is adopted. The Pratt-Hayford isostatic model is then facilitated to estimate the variable Moho density contrast. This variable Moho density contrast is subsequently used to determine the Moho depths. Finally, the combined least-squares approach is applied to estimate jointly the Moho depths and density contract based on a priori error model. The EGM2008 global gravity model and the DTM2006.0 global topographic/bathymetric model are used to generate the isostatic gravity anomalies. The comparison of numerical results reveals that the optimal isostatic inverse scheme should take into consideration both the variable depth and density of compensation. This is achieved by applying the combined least-squares approach for a simultaneous estimation of both Moho parameters. We demonstrate that the result obtained using this method has the best agreement with the CRUST2.0 Moho depths. The numerical experiments are conducted at the regional study area of New Zealand's continental shelf.
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| 2. |
- Bagherbandi, Mohammad, et al.
(författare)
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Improved global crustal thickness modeling based on the VMM isostatic model and non-isostatic gravity correction
- 2013
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707 .- 1879-1670. ; 66, s. 25-37
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Tidskriftsartikel (refereegranskat)abstract
- In classical isostatic models for a gravimetric recovery of the Moho parameters (i.e., Moho depths and density contrast) the isostatic gravity anomalies are usually defined based on the assumption that the topographic mass surplus and the ocean mass deficiency are compensated within the Earth's crust. As acquired in this study, this assumption yields large disagreements between isostatic and seismic Moho models. To assess the effects not accounted for in classical isostatic models, we conduct a number of numerical experiments using available global gravity and crustal structure models. First, we compute the gravitational contributions of mass density contrasts due to ice and sediments, and subsequently evaluate respective changes in the Moho geometry. Residual differences between the gravimetric and seismic Moho models are then used to predict a remaining non-isostatic gravity signal, which is mainly attributed to unmodeled density structures and other geophysical phenomena. We utilize three recently developed computational schemes in our numerical studies. The apparatus of spherical harmonic analysis and synthesis is applied in forward modeling of the isostatic gravity disturbances. The Moho depths are estimated globally on a 1 arc-deg equiangular grid by solving the Vening-Meinesz Moritz inverse problem of isostasy. The same estimation model is applied to evaluate the differences between the isostatic and seismic models. We demonstrate that the application of the ice and sediment density contrasts stripping gravity corrections is essential for a more accurate determination of the Moho geometry. We also show that the application of the additional non-isostatic correction further improves the agreement between the Moho models derived based on gravity and seismic data. Our conclusions are based on comparing the gravimetric results with the CRUST2.0 global crustal model compiled using results of seismic surveys.
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| 3. |
- Bagherbandi, Mohammad, et al.
(författare)
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Moho depth uncertainties in the Vening-Meinesz Moritz inverse problem of isostasy
- 2014
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Ingår i: Studia Geophysica et Geodaetica. - : Springer Science and Business Media LLC. - 0039-3169 .- 1573-1626. ; 58:2, s. 227-248
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Tidskriftsartikel (refereegranskat)abstract
- We formulate an error propagation model based on solving the Vening Meinesz-Moritz (VMM) inverse problem of isostasy. The system of observation equations in the VMM model defines the relation between the isostatic gravity data and the Moho depth by means of a second-order Fredholm integral equation of the first kind. The corresponding error model (derived in a spectral domain) functionally relates the Moho depth errors with the commission errors of used gravity and topographic/bathymetric models. The error model also incorporates the non-isostatic bias which describes the disagreement, mainly of systematic nature, between the isostatic and seismic models. The error analysis is conducted at the study area of the Tibetan Plateau and Himalayas with the world largest crustal thickness. The Moho depth uncertainties due to errors of the currently available global gravity and topographic models are estimated to be typically up to 1-2 km, provided that the GOCE gravity gradient observables improved the medium-wavelength gravity spectra. The errors due to disregarding sedimentary basins can locally exceed similar to 2 km. The largest errors (which cause a systematic bias between isostatic and seismic models) are attributed to unmodeled mantle heterogeneities (including the core-mantle boundary) and other geophysical processes. These errors are mostly less than 2 km under significant orogens (Himalayas, Ural), but can reach up to similar to 10 km under the oceanic crust.
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| 4. |
- Safari, Abdolreza, et al.
(författare)
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Determining the Gravitational Gradient Tensor Using Satellite Altimetry Observations over the Persian Gulf
- 2014
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Ingår i: Marine Geodesy. - : Informa UK Limited. - 0149-0419 .- 1521-060X. ; 37:4, s. 404-418
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Tidskriftsartikel (refereegranskat)abstract
- With the advent of satellite altimetry in 1973, new scientific applications became available in oceanography, climatology, and marine geosciences. Moreover, satellite altimetry provides a significant source of information facilitated in the geoid determination with a high accuracy and spatial resolution. The information from this approach is a sufficient alternate for marine gravity data in the high-frequency modeling of the marine gravity field quantities. The gravity gradient tensor, consisting of the second-order partial derivatives of the gravity potential, provides more localized information than gravity measurements. Marine gravity observations always carry a high noise level due to environmental effects. Moreover, it is not possible to model the high frequencies of the Earth's gravity field in a global scale using these observations. In this article, we introduce a novel approach for a determination of the gravity gradient tensor at sea level using satellite altimetry. Two numerical techniques are applied and compared for this purpose. In particular, we facilitate the radial basis functions (RBFs) and the harmonic splines. As a case study, the gravitational gradient tensor is determined and results presented in the Persian Gulf. Validation of results reveals that the solution of the harmonic spline approach has a better agreement with a theoretical zero-value of the trace of the Marussi gravitational gradient tensor. However, the data-adaptive technique in the RBF approach allows more efficient selection of the parameters and 3-D configuration of RBFs compared to a fixed parameterization by the harmonic splines.
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| 5. |
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| 6. |
- Tenzer, Robert, et al.
(författare)
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Comparative Study of the Uniform and Variable Moho Density Contrast in the Vening Meinesz-Moritz’s Isostatic Scheme for the Gravimetric Moho Recovery
- 2014
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Ingår i: IGFS 2014, Proceedings of the 3rd International Gravity Field Service (IGFS), Shanghai, China, 30 June - 6 July 2014. - Cham : Springer. - 9783319398198 - 9783319819730 ; , s. 199-207
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Konferensbidrag (refereegranskat)abstract
- In gravimetric methods for a determination of the Moho geometry, the constant value of the Moho density contract is often adopted. Results of gravimetric and seismic studies, however, showed that the Moho density contrast varies significantly. The assumption of a uniform density contrast thus might yield large errors in the estimated Moho depths. In this study we investigate these errors by comparing the Moho depths determined globally for the uniform and variable models of the Moho density contrast. These two gravimetric results are obtained based on solving the Vening Meinesz-Moritz’s inverse problem of isostasy. The uniform model of the Moho density contrast is defined individually for the continental and oceanic lithosphere to better reproduce the reality. The global data of the lower crust and upper mantle retrieved from the CRUST1.0 seismic crustal model are used to define the variable Moho density contrast. This seismic model is also used to validate both gravimetric solutions. Results of our numerical experiment reveals that the consideration of the variable Moho density contrast improves the agreement between the gravimetric and seismic Moho models; the RMS of differences is 5.4 km (for the uniform density contrast) and 4.7 km (for the variable density contrast).
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| 7. |
- Tenzer, Robert, et al.
(författare)
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Global model of the upper mantle lateral density structure based on combining seismic and isostatic models
- 2013
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Ingår i: Geosciences Journal. - : Springer Science and Business Media LLC. - 1226-4806 .- 1598-7477. ; 17:1, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- We compile the global model of the upper mantle lateral density structure with a 2x2 arc-deg spatial resolution using the values of the crust-mantle density contrast estimated relative to the adopted crust density model. The combined least-squares approach based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy is facilitated to estimate the crust-mantle density contrast. The global geopotential model (EGM08), the global topographic/bathymetric model (DTM2006.0) including ice-thickness data, and the global crustal model (CRUST2.0) are used to compute the isostatic gravity anomalies. The estimated upper mantle densities globally vary between 2751 and 3635 kg/m(3). The minima correspond with locations of the divergent oceanic tectonic plate boundaries (along the mid-oceanic ridges). The maxima are found along the convergent tectonic plate boundaries in the Andes and Himalayas (extending under the Tibetan Plateau). A comparison of the estimated upper mantle densities with the CRUST2.0 data shows a relatively good agreement between these two models within the continental lithosphere with the differences typically within +/- 100 kg/m(3). Much larger discrepancies found within the oceanic lithosphere are explained by the overestimated values of the CRUST2.0 upper mantle densities. Our result shows a prevailing pattern of increasing densities with the age of oceanic lithosphere which is associated with the global mantle convection process.
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| 8. |
- Tenzer, Robert, et al.
(författare)
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Reformulation of the Vening-Meinesz Moritz Inverse Problem of Isostasy for Isostatic Gravity Disturbances
- 2012
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Ingår i: International Journal of Geosciences. - : Scientific Research Publishing, Inc.. - 2156-8359 .- 2156-8367. ; 3:5A, s. 918-929
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Tidskriftsartikel (refereegranskat)abstract
- The isostatic gravity anomalies have been traditionally used to solve the inverse problems of isostasy. Since gravity measurements are nowadays carried out together with GPS positioning, the utilization of gravity disturbances in various regional gravimetric applications becomes possible. In global studies, the gravity disturbances can be computed using global geopotential models which are currently available to a relatively high accuracy and resolution. In this study we facilitate the definition of the isostatic gravity disturbances in the Vening-Meinesz Moritz inverse problem of isostasy for finding the Moho depths. We further utilize uniform mathematical formalism in the gravimetric forward modelling based on methods for a spherical harmonic analysis and synthesis of gravity field. We then apply both mathematical procedures to determine globally the Moho depths using the isostatic gravity disturbances. The results of gravimetric inversion are finally compared with the global crustal seismic model CRUST2.0; the RMS fit of the gravimetric Moho model with CRUST2.0 is 5.3 km. This is considerably better than the RMS fit of 7.0 km obtained after using the isostatic gravity anomalies.
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| 9. |
- Tenzer, Robert, et al.
(författare)
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Signature of the upper mantle density structure in the refined gravity data
- 2012
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Ingår i: Computational Geosciences. - : Springer Science and Business Media LLC. - 1420-0597 .- 1573-1499. ; 16:4, s. 975-986
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Tidskriftsartikel (refereegranskat)abstract
- The gravitational signal of the upper mantle density structures is investigated in the refined gravity data which are corrected for the gravitational contributions of the crust density structures and the Moho geometry. The gravimetric forward modeling is applied to compute these refined gravity data globally on a 1 x 1 arcdeg grid using the global geopotential model (EGM2008), the global topographic/bathymetric model (DTM2006.0) including the ice-thickness data, and the global crustal model (CRUST2.0). The characteristics of the upper mantle density structures are further analyzed in association with the Moho parameters (i.e., Moho depths and density contrast). The 1 x 1 arcdeg global data of the Moho parameters are estimated by applying the combined least-squares approach based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy. The refined gravity data exhibit mainly the mantle lithosphere structures attributed to the global mantle convection. A significant correlation found over oceans between the refined gravity data and the Moho density contrast is explained by the increasing density of the oceanic lithosphere with age. Despite the lithosphere structures attributed to the global mantle convection are confirmed also in the refined gravity data over continents, the significant correlation between the refined gravity data and the Moho parameters is in this case absent. Instead, the significant proportion of lateral variations of the Moho density contrast within the continental lithosphere is attributed to the depth-dependant density changes due to pressure and thermal gradient.
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