| 1. |
- Novák, P., et al.
(author)
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Evaluation of gravitational gradients generated by Earth's crustal structures
- 2013
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In: Computers & Geosciences. - : Elsevier BV. - 0098-3004 .- 1873-7803. ; 51, s. 22-33
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Journal article (peer-reviewed)abstract
- Spectral formulas for the evaluation of gravitational gradients generated by upper Earth's mass components are presented in the manuscript. The spectral approach allows for numerical evaluation of global gravitational gradient fields that can be used to constrain gravitational gradients either synthesised from global gravitational models or directly measured by the spaceborne gradiometer on board of the GOCE satellite mission. Gravitational gradients generated by static atmospheric, topographic and continental ice masses are evaluated numerically based on available global models of Earth's topography, bathymetry and continental ice sheets. CRUST2.0 data are then applied for the numerical evaluation of gravitational gradients generated by mass density contrasts within soft and hard sediments, upper, middle and lower crust layers. Combined gravitational gradients are compared to disturbing gravitational gradients derived from a global gravitational model and an idealised Earth's model represented by the geocentric homogeneous biaxial ellipsoid GRS80. The methodology could be used for improved modelling of the Earth's inner structure.
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| 2. |
- Tenzer, R., et al.
(author)
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Isostatic crustal thickness under the tibetan plateau and himalayas from satellite gravity gradiometry data
- 2015
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In: Earth Sciences Research Journal. - : Universidad Nacional de Colombia. - 1794-6190 .- 2339-3459. ; 19:2, s. 97-106
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Journal article (peer-reviewed)abstract
- The global gravity and crustal models are used in this study to determine the regional Moho model. For this purpose, we solve the Vening Meinesz-Moritz’s (VMM) inverse problem of isostasy defined in terms of the isostatic gravity gradient. The functional relation between the Moho depth and the second-order radial derivative of the VMM isostatic potential is formulated by means of the (linearized) Fredholm integral equation of the first kind. Methods for a spherical harmonic analysis and synthesis of the gravity field and crustal structure models are applied to evaluate the gravity gradient corrections and the respective corrected gravity gradient, taking into consideration major known density structures within the Earth’s crust (while mantle heterogeneities are disregarded). The resulting gravity gradient is compensated isostatically based on applying the VMM scheme. The VMM inverse problem for finding the Moho depths is solved iteratively. The regularization is applied to stabilize the ill-posed solution. The global geopotential model GOCO-03s, the global topographic/bathymetric model DTM2006.0 and the global crustal model CRUST1.0 are used to generate the VMM isostatic gravity gradient with a spectral resolution complete to a spherical harmonic degree of 250. The VMM inverse scheme is used to determine the regional isostatic crustal thickness beneath the Tibetan Plateau and Himalayas (compiled on a 1x1 arc-deg grid). The differences between the isostatic and seismic Moho models are modeled and subsequently corrected for by applying the non-isostatic correction. Our results show that the regional gravity gradient inversion can model realistically the relative Moho geometry, while the solution contains a systematic bias. We explain this bias by more localized information on the Earth’s inner structure in the gravity gradient field compared to the potential or gravity fields.
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| 3. |
- Tenzer, R., et al.
(author)
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Reference crust-mantle density contrast beneath Antarctica based on the Vening Meinesz-Moritz isostatic inverse problem and CRUST2.0 seismic model
- 2013
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In: Earth Sciences Research Journal. - 1794-6190 .- 2339-3459 .- 1927-0542 .- 1927-0550. ; 17:1, s. 7-12
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Journal article (peer-reviewed)abstract
- The crust-mantle (Moho) density contrast beneath Antarctica was estimated based on solving the Vening Meinesz-Moritz isostatic problem and using constraining information from a seismic global crustal model (CRUST2.0). The solution was found by applying a least-squares adjustment by elements method. Global geopotential model (GOCO02S), global topographic/bathymetric model (DTM2006.0), ice-thickness data for Antarctica (assembled by the BEDMAP project) and global crustal model (CRUST2.0) were used for computing isostatic gravity anomalies. Since CRUST2.0 data for crustal structures under Antarctica are not accurate (due to a lack of seismic data in this part of the world), Moho density contrast was determined relative to a reference homogenous crustal model having 2,670 kg/m3 constant density. Estimated values of Moho density contrast were between 160 and 682 kg/m3. The spatial distribution of Moho density contrast resembled major features of the Antarctic's continental and surrounding oceanic tectonic plate configuration; maxima exceeding 500 kg/m3 were found throughout the central part of East Antarctica, with an extension beneath the Transantarctic mountain range. Moho density contrast in West Antarctica decreased to 400-500 kg/m3, except for local maxima up to ~ 550 kg/m3 in the central Antarctic Peninsula.
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| 4. |
- Tenzer, R., et al.
(author)
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Theoretical deficiencies of isostatic schemes in modeling the crustal thickness along the convergent continental tectonic plate boundaries
- 2016
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In: Journal of Earth Science. - : China University of Geosciences. - 1674-487X .- 1867-111X. ; , s. 1-9
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Journal article (peer-reviewed)abstract
- The results of global and regional studies often show significant disagreement between the Moho depths determined using seismic and isostatic models. In this study, we estimate the differences between these two models in central Eurasia. The Vening Meinesz-Moritz (VMM) inverse problem of isostasy is utilized to determine the isostatic Moho depths. The estimated VMM Moho depths are then corrected for the sediment density contrast. The application of this correction improves the agreement between the isostatic and seismic Moho models. The existing discrepancies between the isostatic and seismic models are finally modeled by applying the non-isostatic correction, which accounts for the unmodelled mantle density heterogeneities and other geodynamic processes, which are not taken into account in classical isostatic models. Our results reveal that the non-isostatic correction still cannot fully describe mechanisms affecting the Moho geometry along the convergent continent-tocontinent tectonic plate boundaries occurring beneath Himalayas despite an overall good performance of the applied method.
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| 5. |
- Bagherbandi, Mohammad, et al.
(author)
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Geoid-to-quasigeoid separation computed using the GRACE/GOCE global geopotential model GOCO02S -A case study of Himalayas and Tibet
- 2013
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In: Terrestrial, Atmospheric and Oceanic Science. - 1017-0839 .- 2223-8964. ; 24:1, s. 59-68
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Journal article (peer-reviewed)abstract
- The geoid-to-quasigeoid correction has been traditionally computed approximately as a function of the planar Bouguer gravity anomaly and the topographic height. Recent numerical studies based on newly developed theoretical models, however, indicate that the computation of this correction using the approximate formula yields large errors especially in mountainous regions with computation points at high elevations. In this study we investigate these approximation errors at the study area which comprises Himalayas and Tibet where this correction reaches global maxima. Since the GPS-leveling and terrestrial gravity datasets in this part of the world are not (freely) available, global gravitational models (GGMs) are used to compute this correction utilizing the expressions for a spherical harmonic analysis of the gravity field. The computation of this correction can be done using the GGM coefficients taken from the Earth Gravitational Model 2008 (EGM08) complete to degree 2160 of spherical harmonics. The recent studies based on a regional accuracy assessment of GGMs have shown that the combined GRACE/GOCE solutions provide a substantial improvement of the Earth's gravity field at medium wavelengths of spherical harmonics compared to EGM08. We address this aspect in numerical analysis by comparing the gravity field quantities computed using the satellite-only combined GRACE/GOCE model GOCO02S against the EGM08 results. The numerical results reveal that errors in the geoid-to-quasigeoid correction computed using the approximate formula can reach as much as ~1.5 m. We also demonstrate that the expected improvement of the GOCO02S gravity field quantities at medium wavelengths (within the frequency band approximately between 100 and 250) compared to EGM08 is as much as ±60 mGal and ±0.2 m in terms of gravity anomalies and geoid/quasigeoid heights respectively.
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| 6. |
- Tenzer, R., et al.
(author)
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Moho interface modeling beneath the himalayas, tibet and central siberia using GOCO02S and DTM2006.0
- 2013
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In: Terrestrial, Atmospheric and Oceanic Science. - 1017-0839 .- 2223-8964. ; 24:4 PART1, s. 581-590
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Journal article (peer-reviewed)abstract
- We apply a newly developed method to estimate the Moho depths and density contrast beneath the Himalayas, Tibet and Central Siberia. This method utilizes the combined least-squares approach based on solving the inverse problem of isostasy and using the constraining information from the seismic global crustal model (CRUST2.0). The gravimetric forward modeling is applied to compute the isostatic gravity anomalies using the global geopotential model (GOCO02S) and the global topographic/ bathymetric model (DTM2006.0). The estimated Moho depths vary between 60 - 70 km beneath most of the Himalayas and Tibet and reach the maxima of ~79 km. The Moho depth under Central Siberia is typically 50 - 60 km. The Moho density contrast computed relative to the CRUST2.0 lower crustal densities has the maxima of ~300 kg m-3 under Central Tibet. It substantially decreases to 150 - 250 kg m-3 under Himalayas and north Tibet. The estimated Moho density contrast under central Siberia is within 100 - 200 kg m-3.
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| 7. |
- Tenzer, R., et al.
(author)
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Depth-dependent density change within the continental upper mantle
- 2012
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In: Contributions to Geophysics and Geodesy. - : Walter de Gruyter GmbH. - 1335-2806 .- 1338-0540. ; 42:1, s. 1-13
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Journal article (peer-reviewed)abstract
- The empirical model of the depth-dependent density change within the upper continental mantle is derived in this study. The density of the upper(most) mantle underlying the continental crust is obtained from the estimated values of the crust-mantle (Moho) density contrast. Since the continental crustal thickness varies significantly, these upper mantle density values to a large extent reflect the density changes with depth. The estimation of the Moho density contrast is done through solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy. The solution combines gravity and seismic data in the least-squares estimation model. The estimated upper mantle density (beneath the continental crust) varies between 2770 and 3649 kg/m 3. The upper mantle density increases almost proportionally with depth at a rate of 13 ± 2 kg/m 3 per 1 km at the investigated depth interval from 6 to 58 km.
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