| 1. |
- Abrehdary, Majid, 1983-, et al.
(författare)
-
A New Moho Depth Model for Fennoscandia with Special Correction for the Glacial Isostatic Effect
- 2021
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Ingår i: Pure and Applied Geophysics. - : Springer Nature. - 0033-4553 .- 1420-9136. ; 178:3, s. 877-888
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we present a new Moho depth model in Fennoscandia and its surroundings. The model is tailored from data sets of XGM2019e gravitationl field, Earth2014 topography and seismic crustal model CRUST1.0 using the Vening Meinesz-Moritz model based on isostatic theory to a resolution of 1° × 1°. To that end, the refined Bouguer gravity disturbance is determined by reducing the observed field for gravity effect of topography, density heterogeneities related to bathymetry, ice, sediments, and other crustal components. Moreover, stripping of non-isostatic effects of gravity signals from mass anomalies below the crust due to crustal thickening/thinning, thermal expansion of the mantle, Delayed Glacial Isostatic Adjustment (DGIA), i.e., the effect of future GIA, and plate flexure has also been performed. As Fennoscandia is a key area for GIA research, we particularly investigate the DGIA effect on the gravity disturbance and gravimetric Moho depth determination in this area. One may ask whether the DGIA effect is sufficiently well removed in the application of the general non-isostatic effects in such an area, and to answer this question, the Moho depth is determined both with and without specific removal of the DGIA effect prior to non-isostatic effect and Moho depth determinations. The numerical results yield that the RMS difference of the Moho depth from our model HVMD19 vs. the seismic CRUST19 and GRAD09 models are 3.8/4.2 km and 3.7/4.0 km when the above strategy for removing the DGIA effect is/is not applied, respectively, and the mean value differences are 1.2/1.4 km and 0.98/1.4 km, respectively. Hence, our study shows that the specific correction for the DGIA effect on gravity disturbance is slightly significant, resulting in individual changes in the gravimetric Moho depth up to − 1.3 km towards the seismic results. On the other hand, our study shows large discrepancies between gravimetric and seismic Moho models along the Norwegian coastline, which might be due to uncompensated non-isostatic effects caused by tectonic motions.
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| 2. |
- Abrehdary, Majid, et al.
(författare)
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Combined Moho parameters determination using CRUST1.0 and Vening Meinesz-Moritz model
- 2015
-
Ingår i: Journal of Earth Science. - : Springer Science and Business Media LLC. - 1674-487X .- 1867-111X. ; 26:4, s. 607-616
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Tidskriftsartikel (refereegranskat)abstract
- According to Vening Meinesz-Moritz (VMM) global inverse isostatic problem, either the Moho density contrast (crust-mantle density contrast) or the Moho geometry can be estimated by solving a non-linear Fredholm integral equation of the first kind. Here solutions to the two Moho parameters are presented by combining the global geopotential model (GOCO-03S), topography (DTM2006) and a seismic crust model, the latter being the recent digital global crustal model (CRUST1.0) with a resolution of 1A(0)x1A(0). The numerical results show that the estimated Moho density contrast varies from 21 to 637 kg/m(3), with a global average of 321 kg/m(3), and the estimated Moho depth varies from 6 to 86 km with a global average of 24 km. Comparing the Moho density contrasts estimated using our leastsquares method and those derived by the CRUST1.0, CRUST2.0, and PREM models shows that our estimate agrees fairly well with CRUST1.0 model and rather poor with other models. The estimated Moho depths by our least-squares method and the CRUST1.0 model agree to 4.8 km in RMS and with the GEMMA1.0 based model to 6.3 km.
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| 3. |
- Abrehdary, Majid, 1983-, et al.
(författare)
-
Contribution of satellite altimetry in modelling Moho density contrast in oceanic areas
- 2019
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Ingår i: Journal of Applied Geodesy. - : WALTER DE GRUYTER GMBH. - 1862-9016 .- 1862-9024. ; 13:1, s. 33-40
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Tidskriftsartikel (refereegranskat)abstract
- The determination of the oceanic Moho (or crust-mantle) density contrast derived from seismic acquisitions suffers from severe lack of data in large parts of the oceans, where have not yet been sufficiently covered by such data. In order to overcome this limitation, gravitational field models obtained by means of satellite altimetry missions can be proficiently exploited, as they provide global uniform information with a sufficient accuracy and resolution for such a task. In this article, we estimate a new Moho density contrast model named MDC2018, using the marine gravity field from satellite altimetry in combination with a seismic-based crustal model and Earth's topographic/bathymetric data. The solution is based on the theory leading to Vening Meinesz-Moritz's isostatic model. The study results in a high-accuracy Moho density contrast model with a resolution of 1° × 1° in oceanic areas. The numerical investigations show that the estimated density contrast ranges from 14.2 to 599.7 kg/m 3 with a global average of 293 kg/m 3 . In order to evaluate the accuracy of the MDC2018 model, the result was compared with some published global models, revealing that our altimetric model is able to image rather reliable information in most of the oceanic areas. However, the differences between this model and the published results are most notable along the coastal and polar zones, which are most likely due to that the quality and coverage of the satellite altimetry data are worsened in these regions.
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| 4. |
- Abrehdary, Majid, 1983-, et al.
(författare)
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Estimating a combined Moho model for marine areas via satellite altimetric : gravity and seismic crustal models
- 2020
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Ingår i: Studia Geophysica et Geodaetica. - : Springer Science and Business Media LLC. - 0039-3169 .- 1573-1626. ; 64, s. 1-25
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Tidskriftsartikel (refereegranskat)abstract
- Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Earth's lithosphere and viscous asthenosphere. A more satisfactory test of isostasy is to determine the depth to and density contrast between crust and mantle at the Moho discontinuity (Moho). Generally, the Moho can be mapped by seismic information, but the limited coverage of such data over large portions of the world (in particular at seas) and economic considerations make a combined gravimetric-seismic method a more realistic approach. The determination of a high-resolution of the Moho constituents for marine areas requires the combination of gravimetric and seismic data to diminish substantially the seismic data gaps. In this study, we estimate the Moho constituents globally for ocean regions to a resolution of 1° × 1° by applying the Vening Meinesz-Moritz method from gravimetric data and combine it with estimates derived from seismic data in a new model named COMHV19. The data files of GMG14 satellite altimetry-derived marine gravity field, the Earth2014 Earth topographic/bathymetric model, CRUST1.0 and CRUST19 crustal seismic models are used in a least-squares procedure. The numerical computations show that the Moho depths range from 7.3 km (in Kolbeinsey Ridge) to 52.6 km (in the Gulf of Bothnia) with a global average of 16.4 km and standard deviation of the order of 7.5 km. Estimated Moho density contrasts vary between 20 kg m-3 (north of Iceland) to 570 kg m-3 (in Baltic Sea), with a global average of 313.7 kg m-3 and standard deviation of the order of 77.4 kg m-3. When comparing the computed Moho depths with current knowledge of crustal structure, they are generally found to be in good agreement with other crustal models. However, in certain regions, such as oceanic spreading ridges and hot spots, we generally obtain thinner crust than proposed by other models, which is likely the result of improvements in the new model. We also see evidence for thickening of oceanic crust with increasing age. Hence, the new combined Moho model is able to image rather reliable information in most of the oceanic areas, in particular in ocean ridges, which are important features in ocean basins.
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| 5. |
- Abrehdary, Majid, et al.
(författare)
-
Modelling Moho depth in ocean areas based on satellite altimetry using Vening Meinesz–Moritz’ method
- 2016
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Ingår i: Acta Geodaetica et Geophysica Hungarica. - : Springer Netherlands. - 1217-8977 .- 1587-1037 .- 2213-5812 .- 2213-5820. ; 51:2, s. 137-149
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Tidskriftsartikel (refereegranskat)abstract
- An experiment for estimating Moho depth is carried out based on satellite altimetryand topographic information using the Vening Meinesz–Moritz gravimetric isostatichypothesis. In order to investigate the possibility and quality of satellite altimetry in Mohodetermination, the DNSC08GRA global marine gravity field model and the DTM2006 globaltopography model are used to obtain a global Moho depth model over the oceans with aresolution of 1 x 1 degree. The numerical results show that the estimated Bouguer gravity disturbancevaries from 86 to 767 mGal, with a global average of 747 mGal, and the estimatedMoho depth varies from 3 to 39 km with a global average of 19 km. Comparing the Bouguergravity disturbance estimated from satellite altimetry and that derived by the gravimetricsatellite-only model GOGRA04S shows that the two models agree to 13 mGal in root meansquare (RMS). Similarly, the estimated Moho depths from satellite altimetry andGOGRA04S agree to 0.69 km in RMS. It is also concluded that possible mean dynamictopography in the marine gravity model does not significantly affect the Moho determination.
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| 6. |
- Abrehdary, Majid, et al.
(författare)
-
Modelling Moho parameters and their uncertainties from the combination of the seismic and satellite gravity data
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a method for estimating a new global Moho model (KTH15C), containing Moho depth and density contrast, from a combination of global models of gravity (GOCO05S), topography (DTM2006) and seismic information (CRUST1.0 and MDN07) to a resolution of 1°×1° based on a solution of Vening Meinesz-Moritz’ inverse problem of isostasy. Particularly, this article has its emphasis on the modelling of the observation standard errors propagated from the Vening Meinesz-Moritz and CRUST1.0 models in estimating the uncertainty of the final Moho model. The numerical results yield Moho depths ranging from 6.5 to 70.1 km, with a global average of 23.4 ± 13 km. The estimated Moho density contrasts range from 21 to 680 kg/m3, with a global average of 345.4 ± 112 kg/m3. Moreover, test computations display that in most areas estimated uncertainties in the parameters are less than 3 km and 50 kg/m3, respectively, but they reach to more significant values under Gulf of Mexico, Chile, Eeastern Mediterranean, Timor sea and parts of polar regions. Comparing the Moho depths estimated by KTH15C and those derived by KTH11C, GEMMA2012C, CRUST1.0, KTH14C, CRUST14 and GEMMA1.0 models shows that KTH15C agree fairly well with CRUST1.0 but rather poor with other models. The Moho density contrasts estimated by KTH15C and those of the KTH11C and KTH14C model agree to 120 and 80 kg/m3 in RMS. The regional numerical studies show that the RMS differences between KTH15C and Moho depths from seismic information yields fits of 2 to 4 km in South and North America, Africa, Europe, Asia, Australia and Antarctica, respectively.
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| 7. |
- Abrehdary, Majid, 1983-, et al.
(författare)
-
Moho density contrast in Antarctica determined by satellite gravity and seismic models
- 2021
-
Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 225:3, s. 1952-1962
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Tidskriftsartikel (refereegranskat)abstract
- As recovering the crust-mantle/Moho density contrast (MDC) significantly depends on the properties of the Earth's crust and upper mantle, varying from place to place, it is an oversimplification to define a constant standard value for it. It is especially challenging in Antarctica, where almost all the bedrock is covered with a thick layer of ice, and seismic data cannot provide a sufficient spatial resolution for geological and geophysical applications. As an alternative, we determine the MDC in Antarctica and its surrounding seas with a resolution of 1 degrees x 1 degrees by the Vening Meinesz-Moritz gravimetric-isostatic technique using the XGM2019e Earth Gravitational Model and Earth2014 topographic/bathymetric information along with CRUST1.0 and CRUST19 seismic crustal models. The numerical results show that our model, named HVMDC20, varies from 81 kg m(-3) in the Pacific Antarctic mid-oceanic ridge to 579 kg m(-3) in the Gamburtsev Mountain Range in the central continent with a general average of 403 kg m(-3). To assess our computations, we compare our estimates with those of some other gravimetric as well as seismic models (KTH11, GEMMA12C, KTH15C and CRUST1.0), illustrating that our estimates agree fairly well with KTH15C and CRUST1.0 but rather poor with the other models. In addition, we compare the geological signatures with HVMDC20, showing how the main geological structures contribute to the MDC. Finally, we study the remaining glacial isostatic adjustment effect on gravity to figure out how much it affects the MDC recovery, yielding a correlation of the optimum spectral window (7 <= n <= 12) between XGM2019e and W12a GIA models of the order of similar to 0.6 contributing within a negligible +/- 14 kg m(-3) to the MDC.
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| 8. |
- Abrehdary, Majid, 1983-, et al.
(författare)
-
Recovering Moho constituents from satellite altimetry and gravimetric data for Europe and surroundings
- 2019
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Ingår i: Journal of Applied Geodesy. - : WALTER DE GRUYTER GMBH. - 1862-9016 .- 1862-9024. ; 13:4, s. 291-303
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Tidskriftsartikel (refereegranskat)abstract
- In this research, we present a local Moho model, named MOHV19, including Moho depth and Moho density contrast (or shortly Moho constituents) with corresponding uncertainties, which are mapped from altimetric and gravimetric data (DSNSC08) in addition to seismic tomographic (CRUST1.0) and Earth topographic data (Earth2014) to a resolution of 1 degrees x 1 degrees based on a solution of Vening Meinesz-Moritz' theory of isostasy. The MOHV19 model covers the area of entire European plate along with the surrounding oceans, bounded by latitudes (30 degrees N-82 degrees N) and longitudes (40 degrees W-70 degrees E). The article aims to interpret the Moho model resulted via altimetric and gravimetric information from the geological and geophysical perspectives along with investigating the relation between the Moho depth and Moho density contrast. Our numerical results show that estimated Moho depths range from 7.5 to 57.9 km with continental and oceanic averages of 41.3 +/- 4.9 km and 21.6 +/- 9.2 km, respectively, and an overall average of 30.9 +/- 12.3 km. The estimated Moho density contrast ranges from 60.2 to 565.8 kg/m(3), with averages of 421.8 +/- 57.9 and 284.4 +/- 62.9 kg/m(3) for continental and oceanic regions, respectively, with a total average of 350.3 +/- 91.5 kg/m(3). In most areas, estimated uncertainties in the Moho constituents are less than 3 km and 40 kg/m(3), respectively, but they reach to much more significant values under Iceland, parts of Gulf of Bothnia and along the Kvitoya Island. Comparing the Moho depths estimated by MOHV19 and those derived by CRUST1.0, MDN07, GRAD09 and MD19 models shows that MOHV19 agree fairly well with CRUST1.0 but rather poor with other models. The RMS difference between the Moho density contrasts estimated by MOHV19 and CRUST1.0 models is 49.45 kg/m(3).
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| 9. |
- Abrehdary, Majid
(författare)
-
Recovering Moho parameters using gravimetric and seismic data
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Isostasy is a key concept in geoscience to interpret the state of mass balance between the Earth’s crust and mantle. There are four well-known isostatic models: the classical models of Airy/Heiskanen (A/H), Pratt/Hayford (P/H), and Vening Meinesz (VM) and the modern model of Vening Meinesz-Moritz (VMM). The first three models assume a local and regional isostatic compensation, whereas the latter one supposes a global isostatic compensation scheme.A more satisfactory test of isostasy is to determine the Moho interface. The Moho discontinuity (or Moho) is the surface, which marks the boundary between the Earth’s crust and upper mantle. Generally, the Moho interface can be mapped accurately by seismic observations, but limited coverage of seismic data and economic considerations make gravimetric or combined gravimetric-seismic methods a more realistic technique for imaging the Moho interface either regional or global scales.It is the main purpose of this dissertation to investigate an isostatic model with respect to its feasibility to use in recovering the Moho parameters (i.e. Moho depth and Moho density contrast). The study is mostly limited to the VMM model and to the combined approach on regional and global scales. The thesis briefly includes various investigations with the following specific subjects:1) to investigate the applicability and quality of satellite altimetry data (i.e. marine gravity data) in Moho determination over the oceans using the VMM model, 2) to investigate the need for methodologies using gravimetric data jointly with seismic data (i.e. combined approach) to estimate both the Moho depth and Moho density contrast over regional and global scales, 3) to investigate the spherical terrain correction and its effect on the VMM Moho determination, 4) to investigate the residual isostatic topography (RIT, i.e. difference between actual topography and isostatic topography) and its effect in the VMM Moho estimation, 5) to investigate the application of the lithospheric thermal-pressure correction and its effect on the Moho geometry using the VMM model, 6) Finally, the thesis ends with the application of the classical isostatic models for predicting the geoid height.The main input data used in the VMM model for a Moho recovery is the gravity anomaly/disturbance corrected for the gravitational contributions of mass density variation due in different layers of the Earth’s crust (i.e. stripping gravity corrections) and for the gravity contribution from deeper masses below the crust (i.e. non-isostatic effects). The corrections are computed using the recent seismic crustal model CRUST1.0.Our numerical investigations presented in this thesis demonstrate that 1) the VMM approach is applicable for estimating Moho geometry using a global marine gravity field derived by satellite altimetry and that the possible mean dynamic topography in the marine gravity model does not significantly affect the Moho determination, 2) the combined approach could help in filling-in the gaps in the seismic models and it also provides good fit to other global and regional models more than 90 per cent of the locations, 3) despite the fact that the lateral variation of the crustal depth is rather smooth, the terrain affects the Moho result most significantly in many areas, 4) the application of the RIT correction improves the agreement of our Moho result with some published global Moho models, 5) the application of the lithospheric thermal-pressure correction improves the agreement of VMM Moho model with some other global Moho models, 6) the geoid height cannot be successfully represented by the classical models due to many other gravitational signals from various mass variations within the Earth that affects the geoid.
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| 10. |
- Abrehdary, Majid, et al.
(författare)
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Remaining non-isostatic effects in isostatic-gravimetric Moho determination-is it needed?
- 2023
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 234:3, s. 2066-2074
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Tidskriftsartikel (refereegranskat)abstract
- For long time the study of the Moho discontinuity (or Moho) has been a crucial topic in inferring the dynamics of the Earth's interior, and with profitable result it is mapped by seismic data, but due to the heterogeneous distribution of such data the quality varies over the world. Nevertheless, with the advent of satellite gravity missions, it is today possible to recover the Moho constituents (i.e. Moho depth; MD and Moho density contrast; MDC) via gravity observations based on isostatic models. Prior to using gravity observations for this application it must be stripped due to the gravitational contributions of known anomalous crustal density structures, mainly density variations of oceans, glacial ice sheets and sediment basins (i.e. stripping gravity corrections). In addition, the gravity signals related mainly with masses below the crust must also be removed. The main purpose of this study is to estimate the significance of removing also remaining non-isostatic effects (RNIEs) on gravity, that is, gravity effects that remain after the stripping corrections. This is carried out by using CRUST19 seismic crustal model and employing Vening Meinesz-Moritz (VMM) gravimetric-isostatic model in recovering the Moho constituents on a global scale to a resolution of 1 degrees x 1 degrees. To reach this goal, we present a new model, named MHUU22, formed by the SGGUGM2 gravitational field, Earth2014 topography, CRUST1.0 and CRUST19 seismic crustal models. Particularly, this study has its main emphasis on the RNIEs on gravity and Moho constituents to find out if we can modify the stripping gravity corrections by a specific correction of the RNIEs. The numerical results illustrate that the RMS differences between MHUU22 MD and the seismic model CRUST1.0 and least-squares combined model MOHV21 are reduced by 33 and 41 per cent by applying the NIEs, and the RMS differences between MHUU22 MDC and the seismic model CRUST1.0 and least-squares combined model MDC21 are reduced by 41 and 23 per cent when the above strategy for removing the RNIEs is applied. Hence, our study demonstrates that the specific correction for the RNIEs on gravity disturbance is significant, resulting in remarkable improvements in MHUU22, which more clearly visualize several crustal structures.
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| 11. |
- Abrehdary, Majid, et al.
(författare)
-
The spherical terrain correction and its effect on the gravimetric-isostatic Moho determination
- 2016
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Ingår i: Geophysical Journal International. - : Oxford University Press. - 0956-540X .- 1365-246X .- 1687-885X .- 1687-8868. ; 204:1, s. 262-273
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the Moho depth is estimated based on the refined spherical Bouguer gravity disturbance and DTM2006 topographic data using the Vening Meinesz-Moritz gravimetric-isostatic hypothesis. In this context, we compute the refined spherical Bouguer gravity disturbances in a set of 1 degrees x 1 degrees blocks. The spherical terrain correction, a residual correction to each Bouguer shell, is computed using rock heights and ice sheet thicknesses from the DTM2006 and Earth2014 models. The study illustrates that the defined simple Bouguer gravity disturbance corrected for the density variations of the oceans, ice sheets and sediment basins and also the non-isostatic effects needs a significant terrain correction to become the refined Bouguer gravity disturbance, and that the isostatic gravity disturbance is significantly better defined by the latter disturbance plus a compensation attraction. Our study shows that despite the fact that the lateral variation of the crustal depth is rather smooth, the terrain affects the result most significantly in many areas. The global numerical results show that the estimated Moho depths by the simple and refined spherical Bouguer gravity disturbances and the seismic CRUST1.0 model agree to 5.6 and 2.7 km in RMS, respectively. Also, the mean value differences are 1.7 and 0.2 km, respectively. Two regional numerical studies show that the RMS differences between the Moho depths estimated based on the simple and refined spherical Bouguer gravity disturbance and that using CRUST1.0 model yield fits of 4.9 and 3.2 km in South America and yield 3.2 and 3.4 km in Fennoscandia, respectively.
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| 12. |
- Abrehdary, Majid, et al.
(författare)
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Towards the Moho depth and Moho density contrast along with their uncertainties from seismic and satellite gravity observations
- 2017
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 11:4, s. 231-247
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined method for estimating a new global Moho model named KTH15C, containing Moho depth and Moho density contrast (or shortly Moho parameters), from a combination of global models of gravity (GOCO05S), topography (DTM2006) and seismic information (CRUST1.0 and MDN07) to a resolution of 1° × 1° based on a solution of Vening Meinesz-Moritz’ inverse problem of isostasy. This paper also aims modelling of the observation standard errors propagated from the Vening Meinesz-Moritz and CRUST1.0 models in estimating the uncertainty of the final Moho model. The numerical results yield Moho depths ranging from 6.5 to 70.3 km, and the estimated Moho density contrasts ranging from 21 to 650 kg/m3, respectively. Moreover, test computations display that in most areas estimated uncertainties in the parameters are less than 3 km and 50 kg/m3, respectively, but they reach to more significant values under Gulf of Mexico, Chile, Eastern Mediterranean, Timor sea and parts of polar regions. Comparing the Moho depths estimated by KTH15C and those derived by KTH11C, GEMMA2012C, CRUST1.0, KTH14C, CRUST14 and GEMMA1.0 models shows that KTH15C agree fairly well with CRUST1.0 but rather poor with other models. The Moho density contrasts estimated by KTH15C and those of the KTH11C, KTH14C and VMM model agree to 112, 31 and 61 kg/m3 in RMS. The regional numerical studies show that the RMS differences between KTH15C and Moho depths from seismic information yields fits of 2 to 4 km in South and North America, Africa, Europe, Asia, Australia and Antarctica, respectively.
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| 13. |
- Bagherbandi, Mohammad, et al.
(författare)
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A new Fennoscandian crustal thickness model based on CRUST1.0 and a gravimetric-isostatic approach
- 2015
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 145, s. 132-145
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Forskningsöversikt (refereegranskat)abstract
- In this paper a new gravimetric-isostatic crustal thickness model (VMM14_FEN) is estimated for Fennoscandia. The main motivation is to investigate the relations between geological and geophysical properties, the Moho depth and crust-mantle density contrast at the crust-mantle discontinuity. For this purpose the Bouguer gravity disturbance data is corrected in two main ways namely for the gravitational contributions of mass density variation due to the different layers of the Earth's crust such as ice and sediments, as well as for the gravitational contribution from deeper masses below the crust. This second correction (for non-isostatic effects) is necessary because in general the crust is not in complete isostatic equilibrium and the observed gravity data are not only generated by the topographic/isostatic masses but also from those in the deep Earth interior. The correction for non-isostatic effects is mainly attributed to unmodeled mantle and core boundary density heterogeneities. These corrections are determined using the recent seismic crustal thickness model CRUST1.0. We compare our modeling results with previous studies in the area and test the fitness. The comparison with the external Moho model EuCRUST-07 shows a 3.3. km RMS agreement for the Moho depth in Fennoscandia. We also illustrate how the above corrections improve the Moho depth estimation. Finally, the signatures of geological structures and isostatic equilibrium are studied using VMM14_FEN, showing how main geological unit structures attribute in isostatic balance by affecting the Moho geometry. The main geological features are also discussed in the context of the complete and incomplete isostatic equilibrium.
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| 14. |
- Bagherbandi, Mohammad, et al.
(författare)
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Effect of the lithospheric thermal state on the Moho geometry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Gravimetric methods applied for a Moho recovery in areas with sparse and irregular distribution of seismic data often assume only a constant crustal density. Results of the latest studies, however, indicate that corrections for the crustal density heterogeneities could improve the gravimetric result especially in regions with a complex geologic/tectonic structure. Moreover, the isostatic mass balance reflects also the density structure within the mantle. The gravimetric methods should therefore incorporate an additional correction for the sub-crustal density heterogeneities. Following this principle, we solve the Vening Meinesz-Moritz (VMM) inverse problem of isostasy constrained on seismic data to determine the Moho depth of the South American tectonic plate including surrounding oceans, while taking into consideration the crustal and mantle density heterogeneities. Our numerical result confirms that the contribution of sediments significantly modifies the Moho geometry especially along the continental margins with large sediment deposits. To account for the mantle density heterogeneities we develop and apply a method of correcting the Moho geometry for the contribution of the lithospheric thermal state (i.e., the lithospheric thermal-pressure correction). In addition, the misfit between the isostatic and seismic Moho models, attributed mainly to deep mantle density heterogeneities and other geophysical phenomena, is corrected for by applying the non-isostatic correction. The results reveal that the application of the lithospheric thermal-pressure correction improves the RMS fit of the VMM gravimetric Moho solution to the CRUST1.0 seismic model and the point-wise seismic data in South America about 40% and 7% respectively.
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| 15. |
- Bagherbandi, Mohammad, et al.
(författare)
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Effect of the lithospheric thermal state on the Moho interface : a case study in South America
- 2017
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Ingår i: Journal of South American Earth Sciences. - : Elsevier BV. - 0895-9811 .- 1873-0647. ; 76, s. 198-207
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Tidskriftsartikel (refereegranskat)abstract
- Gravimetric methods applied for Moho recovery in areas with sparse and irregular distribution of seismic data often assume only a constant crustal density. Results of latest studies, however, indicate that corrections for crustal density heterogeneities could improve the gravimetric result, especially in regions with a complex geologic/tectonic structure. Moreover, the isostatic mass balance reflects also the density structure within the lithosphere. The gravimetric methods should therefore incorporate an additional correction for the lithospheric mantle as well as deeper mantle density heterogeneities. Following this principle, we solve the Vening Meinesz-Moritz (VMM) inverse problem of isostasy constrained by seismic data to determine the Moho depth of the South American tectonic plate including surrounding oceans, while taking into consideration the crustal and mantle density heterogeneities. Our numerical result confirms that contribution of sediments significantly modifies the estimation of the Moho geometry especially along the continental margins with large sediment deposits. To account for the mantle density heterogeneities we develop and apply a method in order to correct the Moho geometry for the contribution of the lithospheric thermal state (i.e., the lithospheric thermal-pressure correction). In addition, the misfit between the isostatic and seismic Moho models, attributed mainly to deep mantle density heterogeneities and other geophysical phenomena, is corrected for by applying the non-isostatic correction. The results reveal that the application of the lithospheric thermal-pressure correction improves the RMS fit of the VMM gravimetric Moho solution to the CRUST1.0 (improves ∼ 1.9 km) and GEMMA (∼1.1 km) models and the point-wise seismic data (∼0.7 km) in South America.
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| 16. |
- Bagherbandi, Mohammad, et al.
(författare)
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On the residual isostatic topography effect in the gravimetric Moho determination
- 2015
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707 .- 1879-1670. ; 83, s. 28-36
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Tidskriftsartikel (refereegranskat)abstract
- In classical isostatic models, a uniform crustal density is typically assumed, while disregarding the crustal density heterogeneities. This assumption, however, yields large errors in the Moho geometry determined from gravity data, because the actual topography is not fully isostatically compensated. Moreover, the sub-crustal density structures and additional geodynamic processes contribute to the overall isostatic balance. In this study we investigate the effects of unmodelled density structures and geodynamic processes on the gravity anomaly and the Moho geometry. For this purpose, we define the residual isostatic topography as the difference between actual topography and isostatic topography, which is computed based on utilizing the Vening Meinesz-Moritz isostatic theory. We show that the isostatic gravity bias due to disagreement between the actual and isostatically compensated topography varies between -382 and 596 mGal. This gravity bias corresponds to the Moho correction term of -16 to 25 km. Numerical results reveal that the application of this Moho correction to the gravimetrically determined Moho depths significantly improves the RMS fit of our result with some published global seismic and gravimetric Moho models. We also demonstrate that the isostatic equilibrium at long-to-medium wavelengths (up to degree of about 40) is mainly controlled by a variable Moho depth, while the topographic mass balance at a higher-frequency spectrum is mainly attained by a variable crustal density.
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| 17. |
- Kiamehr, R., et al.
(författare)
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Combination of satellite altimetry data and EGM2008 model for evaluation of the height datum in Iran
- 2011
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Ingår i: Ecology, Environment and Conservation. - 0971-765X. ; 17:4, s. 653-659
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Tidskriftsartikel (refereegranskat)abstract
- The repetitive periodic coverage from Topex/Poseidon altimetry satellite during 1992-2003 from the Oman Sea and Persian Gulf were used to prepare time series covering the study area. The linear portion of series were analyzed to calculate mean sea level as its temporal changes using the least-squares method. Due to the significance of sea level topography in oceanographic studies a new model proposed using the combined altimetry satellite data and the EGM2008 global geoid model in order to determine and equalize the current height datum for Iran. The maximum and minimum of sea surface topography vary within the range of -0.7 to 1.1m in the study area. Adjustment of the current precise network for Iran established based on the Bandar Abbas tide gauge station, which its corresponding SST estimated up to -0.5 m. Effect of such large systematic error in national height system cannot be ignored in geodynamical and engineering researches.
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| 18. |
- Saberi, Azim, et al.
(författare)
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Accuracy assessment and improvement of SRTM, ASTER, FABDEM, and MERIT DEMs by polynomial and optimization algorithm : A case study (Khuzestan Province, Iran)
- 2023
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Ingår i: Open Geosciences. - : De Gruyter Open. - 2391-5447. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- Satellite digital elevation models (DEMs) are used for decision-making in various fields. Therefore, evaluating and improving vertical accuracy of DEM can increase the quality of end products. This article aimed to increase the vertical accuracy of most popular satellite DEMs (i.e., the ASTER, Shuttle Radar Topography Mission [SRTM], Forest And Buildings removed Copernicus DEM [FABDEM], and Multi-Error-Removed Improved-Terrain [MERIT]) using the particle swarm optimization (PSO) algorithm. For this purpose, at first, the vertical error of DEMs was estimated via ground truth data. Next, a second-order polynomial was applied to model the vertical error in the study area. To select the polynomial with the highest accuracy, employed for vertical error modeling, the coefficients of the polynomial have been optimized using the PSO algorithm. Finally, the efficiency of the proposed algorithm has been evaluated by other ground truth data and in situ observations. The results show that the mean absolute error (MAE) of SRTM DEM is 4.83 m while this factor for ASTER DEM is 5.35 m, for FABDEM is 4.28, and for MERIT is 3.87. The obtained results indicated that the proposed model could improve the MAE of vertical accuracy of SRTM, ASTER, FABDEM, and MERIT DEMs to 0.83, 0.51, 0.37, and 0.29 m, respectively.
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| 19. |
- Sadatipour, S. M. T., et al.
(författare)
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The Evaluation of Sea Surface Topography Models based on the Combination of the Satellite altimetry and the Global Geoid Models in the Persian Gulf
- 2012
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Ingår i: International Journal of Environmental Research. - 1735-6865 .- 2008-2304. ; 6:3, s. 645-652
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Tidskriftsartikel (refereegranskat)abstract
- One of the difficulties in using absolute altitudes is the separation between the mean open sea level and geoid. Theoretically, geoid is the base level in absolute altitudes, but practically, the mean open sea level is used as a base level for absolute altitudes. The difference between these two levels is called as the sea surface topography. In this research, it is dealt the mean sea level modeling by using the observations of three altimeter satellites (i.e. Topex/Poseidon, Jason-1 and GFO) in Persian Gulf and then it is dealt with the evaluation of existing models of the sea surface topography based on the altimeter satellites data and the global geopotential geoid models (i.e. European Improved Gravity model of the Earth by New techniques, Gravity field and steady-state Ocean Circulation Explorer, Earth Gravitational Model 2008. The results of this research indicate that the sea surface topographical model resulting from the EIGEN06C geoid is the most precise model with changes range between -2.482 m and -1.511 m and mean -0.23 m.
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| 20. |
- Sjöberg, Lars, 1947-, et al.
(författare)
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Combination of three global Moho density contrast models by a weighted least-squares procedure
- 2022
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 16:4, s. 331-339
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Tidskriftsartikel (refereegranskat)abstract
- Due to different structures of the Earth's crust and mantle, there is a significant density contrast at their boundary, the Moho Density Contrast (or shortly MDC). Frequently one assumes that the MDC is about 600 kg/m3, but seismic and gravimetric data show a considerable variation from region to region, and today there are few such studies, and global models are utterly rare. This research determines a new global model, called MDC21, which is a weighted least-squares combination of three available MDC models, pixel by pixel at a resolution of 1° × 1°. For proper weighting among the models, the study starts by estimating lacking standard errors and (frequently high) correlations among them. The numerical investigation shows that MDC21 varies from 21 to 504 kg/m3 in ocean areas and ranges from 132 to 629 kg/m3 in continental regions. The global average is 335 kg/m3. The standard errors estimated in ocean regions are mostly less than 40 kg/m3, while for continental regions it grows to 80 kg/m3. Most standard errors are small, but they reach to notable values in some specific regions. The estimated MDCs (as well as Moho depths) at mid-ocean ridges are small but show significant variations and qualities.
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| 21. |
- Sjöberg, Lars E., et al.
(författare)
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On Moho Determination by the Vening Meinesz-Moritz Technique
- 2021
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Ingår i: Geodetic Sciences. - : INTECH. ; , s. 1-19
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Bokkapitel (refereegranskat)abstract
- This chapter describes a theory and application of satellite gravity and altimetry data for determining Moho constituents (i.e. Moho depth and density contrast) with support from a seismic Moho model in a least-squares adjustment. It presents and applies the Vening Meinesz-Moritz gravimetric-isostatic model in recovering the global Moho features. Internal and external uncertainty estimates are also determined. Special emphasis is devoted to presenting methods for eliminating the so-called non-isostatic effects, i.e. the gravimetric signals from the Earth both below the crust and from partly unknown density variations in the crust and effects due to delayed Glacial Isostatic Adjustment as well as for capturing Moho features not related with isostatic balance. The global means of the computed Moho depths and density contrasts are 23.8±0.05 km and 340.5 ± 0.37 kg/m3, respectively. The two Moho features vary between 7.6 and 70.3 km as well as between 21.0 and 650.0 kg/m3. Validation checks were performed for our modeled crustal depths using a recently published seismic model, yielding an RMS difference of 4 km.
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| 22. |
- Sjöberg, Lars E., 1947-, et al.
(författare)
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The uncertainty of CRUST1.0 Moho depth and density contrast models
- 2021
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 15:2, s. 143-152
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Tidskriftsartikel (refereegranskat)abstract
- As crustal structure models based on seismic and other data are frequently used as a-priori information for further geophysical and geological studies and interpretations (e. g., for gravity inversion), it is important to accurately document their qualities. For instance, the uncertainties in published crustal structures deeply affect the accuracies of produced Moho contour maps. The qualities in seismic crustal models arise from several factors such as the survey method, the spatial resolution of the survey (for example the spacing of the shot points and the recording stations), and the analytical techniques utilized to process the data. It is difficult to determine the uncertainties associated with seismic based crustal depth/Moho depth (MD) models, and even more difficult to use such data for estimating the Moho density contrast (MDC) and its accuracy. However, there is another important observable available today, namely global satellite gravitational data, which are fairly homogeneous v. r. t. accuracy and distribution over the planet. For instance, we find by simple error propagation, using the error covariance matrix of the GOCE TIM5 gravitational model, that this model can determine the MD to a global RMS error of 0.8 km with a resolution of about 1 degrees for a known MDC of 200 kg/m(3). However, the uncertainty in the MDC will further deteriorate the result. We present a new method for estimating the MD and MDC uncertainties of one model by comparing it with another (correlated or uncorrelated) model with known uncertainty. The method is applied in estimating the uncertainty for the CRUST1.0 MD model from four global models (CRUST19, MDN07, GEMMA1.0, KTH15C), yielding mean standard errors varying between 2 and 4.9 km in ocean regions and between 3.2 and 6.0 km on land regions with overall means of 3.8 +/- 0.4 and 4.8 +/- 0.6 km, respectively. Also, starting from the KTH15C MDC model, the mean standard error of CRUST1.0 MDC was estimated to 47.4 and 48.3 kg/m(3) for ocean and land regions, respectively.
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| 23. |
- Sjöberg, Lars, 1947-, et al.
(författare)
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Geoid or Quasi-Geoid? A Short Comparison
- 2024
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Ingår i: X Hotine-Marussi Symposium on Mathematical Geodesy - Proceedings of the Symposium, 2022. - : Springer Nature. ; , s. 171-174
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Konferensbidrag (refereegranskat)abstract
- This article is a short introduction to the debate on choosing the geoid and orthometric heights or the quasi-geoid and normal heights as the vertical coordinate system. It mainly compiles some more or less already known facts for comparing the two systems.
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| 24. |
- Sjöberg, Lars, et al.
(författare)
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The observed geoid height versus Airy's and Pratt's isostatic models using matched asymptotic expansions
- 2014
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Ingår i: Acta Geodaetica et Geophysica Hungarica. - : Springer Netherlands. - 1217-8977 .- 1587-1037 .- 2213-5812 .- 2213-5820. ; 49:4, s. 473-490
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Tidskriftsartikel (refereegranskat)abstract
- Isostasy is a key concept in geodesy and geophysics. The classical isostatic models of Airy/Heiskanen and Pratt/Hayford imply that the topographic mass surplus and ocean mass deficit are balanced by mountain roots and anti-roots in the former model and by density variations in the topography and the compensation layer below sea bottom in the latter model. In geophysics gravity inversion is an essential topic where isostasy comes to play. The main objective of this study is to compare the prediction of geoid heights from the above isostatic models based on matched asymptotic expansion with geoid heights observed by the Earth Gravitational Model 2008. Numerical computations were carried out both globally and in several regions, showing poor agreements between the theoretical and observed geoid heights. As an alternative, multiple regression analysis including several non-isostatic terms in addition to the isostatic terms was tested providing only slightly better success rates. Our main conclusion is that the geoid height cannot generally be represented by the simple formulas based on matched asymptotic expansions. This is because (a) both the geoid and isostatic compensation of the topography have regional to global contributions in addition to the pure local signal considered in the classical isostatic models, and (b) geodynamic phenomena are still likely to significantly blur the results despite that all spherical harmonic low-degree (below degree 11) gravity signals were excluded from the study.
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