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Eshagh, Mehdi, ProfessorORCID iD iconorcid.org/0000-0003-0067-8631
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Publications (10 of 70) Show all publications
Eshagh, M. & Pitoňák, M. (2019). Elastic Thickness Determination from on-orbit GOCE Data and CRUST1.0. Pure and Applied Geophysics, 176(2), 685-696
Open this publication in new window or tab >>Elastic Thickness Determination from on-orbit GOCE Data and CRUST1.0
2019 (English)In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 176, no 2, p. 685-696Article in journal (Refereed) Published
Abstract [en]

Elastic thickness (Te) is a parameter representing the lithospheric strength with respect to the loading. Those places, having large values of elastic thickness, flexes less. In this paper, the on-orbit measured gravitational gradients of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission are used for determining the elastic thickness over Africa. A forward computational method is developed based on the Vening Meinesz-Moritz (VMM) and flexural theories of isostasy to find a mathematical relation between the second-order derivative of the Earth’s gravity field measured by the GOCE satellite and mechanical properties of the lithosphere. The loading of topography and bathymetry, sediments and crystalline masses are computed from CRUST1.0, in addition to estimates of laterally-variable density of the upper mantle, Young’s modulus and Poisson’s ratio. The second-order radial derivatives of the gravitational potential are synthesised from the crustal model and different a priori values of elastic thickness to find which one matches the GOCE on-orbit gradient. This method is developed in terms of spherical harmonics and performed at any point along the GOCE orbit without using any planar approximation. Our map of Te over Africa shows that the intra-continental hotspots and volcanoes, such as Ahaggar, Tibesti, Darfur, Cameroon volcanic line and Libya are connected by corridors of low Te. The high values of Te are mainly associated with the cratonic areas of Congo, Chad and the Western African basin.

Keywords
Elastic thickness, Forward modelling, GOCE gravitational gradients, Isostasy
National Category
Geophysics
Research subject
ENGINEERING, Geodesy
Identifiers
urn:nbn:se:hv:diva-13113 (URN)10.1007/s00024-018-2018-3 (DOI)000460039400010 ()2-s2.0-85062302204& (Scopus ID)
Note

First Online: 06 November 2018

Funders: Czech Science Foundation, GA18-06943S

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2019-03-21Bibliographically approved
Eshagh, M., Pitonak, M. & Tenzer, R. (2019). Lithospheric elastic thickness estimates in central Eurasia. Terrestrial, Atmospheric and Oceanic Science, 30(1), 73-84
Open this publication in new window or tab >>Lithospheric elastic thickness estimates in central Eurasia
2019 (English)In: Terrestrial, Atmospheric and Oceanic Science, ISSN 1017-0839, E-ISSN 2223-8964, Vol. 30, no 1, p. 73-84Article in journal (Refereed) Published
Abstract [en]

We estimate the elastic thickness of a continental lithosphere by using two approaches that combine the Vening Meinesz-Moritz (VMM) regional isostatic principle with isostatic flexure models formulated based on solving flexural differential equations for a thin elastic shell with and without considering a shell curvature. To model the response of the lithosphere on a load more realistically, we also consider lithospheric density heterogeneities. Resulting expressions describe a functional relation between gravity field quantities and mechanical properties of the lithosphere, namely Young’s modulus and Poisson’s ratio that are computed from seismic velocity models in prior of estimating the lithospheric elastic thickness. Our numerical study in central Eurasia reveals that both results have a similar spatial pattern, despite exhibiting also some large localized differences due to disregarding the shell curvature. Results show that cratonic formations of North China and Tarim Cratons, Turan Platform as well as parts of Siberian Craton are characterized by the maximum lithospheric elastic thickness. Indian Craton, on the other hand, is not clearly manifested. Minima of the elastic thickness typically correspond with locations of active continental tectonic margins, major orogens (Tibet, Himalaya and parts of Central Asian Orogenic Belt) and an extended continental crust. These findings generally support the hypothesis that tectonically active zones and orogens have a relatively small lithospheric strength, resulting in a significant respond of the lithosphere on various tectonic loads, compared to a large lithospheric strength of cratonic formations.

Keywords
Cratons, Elastic thickness, Flexure, Isostasy, Lithosphere, Orogens
National Category
Earth and Related Environmental Sciences
Research subject
ENGINEERING, Geodesy
Identifiers
urn:nbn:se:hv:diva-13844 (URN)10.3319/TAO.2018.09.28.02 (DOI)000461562200007 ()2-s2.0-85063267038 (Scopus ID)
Note

Funders: Czech Science Foundation, GA18-06943S 

Available from: 2019-05-24 Created: 2019-05-24 Last updated: 2019-07-25Bibliographically approved
Sundararajan, N., Eshagh, M., Saibi, H., Meghraoui, M., Al-Garni, M. & Giroux, B. (Eds.). (2019). On Significant Applications of Geophysical Methods: Proceedings of the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 2018. Cham: Springer International Publishing
Open this publication in new window or tab >>On Significant Applications of Geophysical Methods: Proceedings of the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 2018
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2019 (English)Collection (editor) (Other academic)
Abstract [en]

This edited volume is based on the best papers accepted for presentation during the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 2018. This special volume is of interest to all researchers practicing geosphysicists/seismologists, students of PG and UG in the fields of multifaceted Geoscience. Major applications with relevant illustrations presented in the volume are from Middle East. And therefore, this book no doubt would serve as a reference guide to all geoscientists and students in the broad field of Earth Science. This volume covers significant applications of gravity and magnetic methods, electrical and electromagnetic methods, refraction and reflection seismic methods besides a large number of study on earthquakes, tectonics and geological settings etc. The salient features of this volume are the interpretation and modeling of geophysical data of different nature

Place, publisher, year, edition, pages
Cham: Springer International Publishing, 2019. p. 190
Series
Advances in Science, Technology & Innovation, ISSN 2522-8714, E-ISSN 2522-8722
National Category
Geophysics
Research subject
ENGINEERING, Geodesy
Identifiers
urn:nbn:se:hv:diva-13745 (URN)10.1007/978-3-030-01656-2 (DOI)978-3-030-01655-5 (ISBN)978-3-030-01656-2 (ISBN)
Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-03-21
Eshagh, M., Johansson, F., Karlsson, L. & Horemuz, M. (2018). A case study on displacement analysis of Vasa warship. Journal of Geodetic Science, 8(1), 43-54
Open this publication in new window or tab >>A case study on displacement analysis of Vasa warship
2018 (English)In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 8, no 1, p. 43-54Article in journal (Refereed) Published
Abstract [en]

Monitoring deformation of man-made structures is very important to prevent them from a risk of collapse and save lives. Such a process is also used for monitoring change in historical objects, which are deforming continuously with time. An example of this is the Vasa warship, which was under water for about 300 years. The ship was raised from the bottom of the sea and is kept in the Vasa museum in Stockholm. A geodetic network with points on the museum building and the ship's body has been established and measured for 12 years for monitoring the ship's deformation. The coordinate time series of each point on the ship and their uncertainties have been estimated epoch-wisely. In this paper, our goal is to statistically analyse the ship's hull movements. By fitting a quadratic polynomial to the coordinate time series of each point of the hull, its acceleration and velocity are estimated. In addition, their significance is tested by comparing them with their respective estimated errors after the fitting. Our numerical investigations show that the backside of the ship, having highest elevation and slope, has moved vertically faster than the other places by a velocity and an acceleration of about 2 mm/year and 0.1 mm/year2, respectively and this part of the ship is the weakest with a higher risk of collapse. The central parts of the ship are more stable as the ship hull is almost vertical and closer to the floor. Generally, the hull is moving towards its port and downwards

Keywords
error estimation; coordinate and displacement time series; significance test
National Category
Infrastructure Engineering
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12231 (URN)10.1515/jogs-2018-0006 (DOI)000438302000006 ()
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2019-05-24Bibliographically approved
Eshagh, M., Steinberger, B., Tenzer, R. & Tassara, A. (2018). Comparison of gravimetric and mantle flow solutions for sub-lithopsheric stress modeling and their combination. Geophysical Journal International, 213(2), 1013-1028
Open this publication in new window or tab >>Comparison of gravimetric and mantle flow solutions for sub-lithopsheric stress modeling and their combination
2018 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 213, no 2, p. 1013-1028Article in journal (Refereed) Published
Abstract [en]

Based on Hager and O’Connell’s solution to mantle flow equations, the stresses induced by mantle convection are determined using the density and viscosity structure in addition to topographic data and a plate velocity model. The solution to mantle flow equations requires the knowledge of mantle properties that are typically retrieved from seismic information. Large parts of the world are, however, not yet covered sufficiently by seismic surveys. An alternative method of modeling the stress field was introduced by Runcorn. He formulated a direct relation between the stress field and gravity data, while adopting several assumptions, particularly disregarding the toroidal mantle flow component and mantle viscosity variations. A possible way to overcome theoretical deficiencies of Runcorn’s theory as well as some practical limitations of applying Hager and O’Connell’s theory (in the absence of seismic data) is to combine these two methods. In this study, we apply a least-squares analysis to combine these two methods based on the gravity data inversion constraint on mantle flow equations. In particular, we use vertical gravity gradients from the Gravity field and steady state Ocean Circulation Explorer that are corrected for the gravitational contribution of crustal density heterogeneities prior to applying a localized gravity-gradient inversion. This gravitational contribution is estimated based on combining the Vening Meinesz-Moritz and flexural isostatic theories. Moreover, we treat the non-isostatic effect implicitly by applying a band-limited kernel of the integral equation during the inversion. In numerical studies of modeling, the stress field within the South American continental lithosphere we compare the results obtained after applying Runcorn and Hager and O’Connell’s methods as well as their combination. The results show that, according to Hager and O’Connell’s (mantle flow) solution, the maximum stress intensity is inferred under the northern Andes. Additional large stress anomalies are detected along the central and southern Andes, while stresses under most of old, stable cratonic formations aremuch less pronounced or absent. A prevailing stress-vector orientation realistically resembles a convergent mantle flow and downward currents under continental basins that separate Andean Orogeny from the Amazonian Shield and adjacent cratons. Runcorn’s (gravimetric) solution, on the other hand, reflects a tectonic response of the lithosphere to mantle flow, with the maximum stress intensity detected along the subduction zone between the Nazca and Altiplano plates and along the convergent tectonic margin between the Altiplano and South American plates. The results also reveal a very close agreement between the results obtained from the combined and Hager and O’Connell’s solutions. © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Keywords
Gravitation; Integral equations; Least squares approximations; Lithology; Numerical methods; Plates (structural components); Seismology; Stresses; Structural geology; Viscosity, Continental basins; Continental lithosphere; Gravity anomalies and Earth structures; Gravity field and steady state ocean circulation explorers; Least squares analysis; Maximum stress intensity; Satellite gravity; Seismic information, Tectonics
National Category
Geophysics
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12246 (URN)10.1093/gji/ggy033 (DOI)000448720300021 ()2-s2.0-85044350246 (Scopus ID)
Available from: 2018-04-09 Created: 2018-04-09 Last updated: 2019-05-28Bibliographically approved
Eshagh, M. (2018). Elastic thickness determination based on Vening Meinesz-Moritz and flexural theories of isostasy. Geophysical Journal International, 213(3), 1682-1692
Open this publication in new window or tab >>Elastic thickness determination based on Vening Meinesz-Moritz and flexural theories of isostasy
2018 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 213, no 3, p. 1682-1692Article in journal (Refereed) Published
Abstract [en]

Elastic thickness (Te) is one of mechanical properties of the Earth's lithosphere. The lithosphere is assumed to be a thin elastic shell, which is bended under the topographic, bathymetric and sediment loads on. The flexure of this elastic shell depends on its thickness or Te. Those shells having larger Te flex less. In this paper, a forward computational method is presented based on the Vening Meinesz–Moritz (VMM) and flexural theories of isostasy. Two Moho flexure models are determined using these theories, considering effects of surface and subsurface loads. Different values are selected for Te in the flexural method to see by which one, the closest Moho flexure to that of the VMM is achieved. The effects of topographic/bathymetric, sediments and crustal crystalline masses, and laterally variable upper mantle density, Young's modulus and Poisson's ratio are considered in whole computational process. Our mathematical derivations are based on spherical harmonics, which can be used to estimate Te at any single point, meaning that there is no edge effect in the method. However, the Te map needs to be filtered to remove noise at some points. A median filter with a window size of 5° × 5° and overlap of 4° works well for this purpose. The method is applied to estimate Te over South America using the data of CRUST1.0 and a global gravity model.

Keywords
GEODESY and GRAVITY, Gravity anomalies and Earth structure, Loading of the Earth
National Category
Geophysics
Identifiers
urn:nbn:se:hv:diva-12170 (URN)10.1093/gji/ggy075 (DOI)000434675800017 ()2-s2.0-85052655258 (Scopus ID)
Available from: 2018-02-26 Created: 2018-02-26 Last updated: 2018-09-27Bibliographically approved
Zampal, L., Tenzer, R., Eshagh, M. & Pitonak, M. (2018). Evidence of mantle upwelling/downwelling and localized subduction on Venus from the body-force vector analysis. Planetary and Space Science, 157, 48-62
Open this publication in new window or tab >>Evidence of mantle upwelling/downwelling and localized subduction on Venus from the body-force vector analysis
2018 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 157, p. 48-62Article in journal (Refereed) Published
Abstract [en]

Considering that Venus has a size very similar to Earth, thermal evolution of both planets should be comparable. Nonetheless, there is no clear evidence of plate tectonics or plate motions on Venus. Instead, various surface deformations attributed to volcanism, resurfacing, localized subduction and other geologic processes were recognized on the planet. In this study we attempt to classify the origin of lithospheric forces on Venus based on using topographic and gravity information. For this purpose, we also estimate the Venusian crustal thickness. In agreement with findings from previous studies, the signature of past or recent global tectonism in the body-force vector pattern on Venus is absent, while exhibiting only regional anomalies. The maximum intensity inferred in the Atla and Beta Regios is likely attributed to mantle upwelling. This is also confirmed by the gravity-topography spectral correlation and admittance analysis that shows the isostatic relaxation of these volcanic regions. The regional body-force pattern in the Bell Regio suggests that a much less pronounced force intensity there is possibly related to crustal load of lava flows. Elsewhere, the body-force intensity is relatively weak, with slightly more pronounced intensity around the Ishtar Terra and the Arthemis Chasmata. The body-force pattern in the Arthemis Chasmata supports the hypothesis that coronae structures are the result of mantle upwelling and the subsequent (localized) plume-induced subduction with only limited horizontal crustal motions. The prevailing divergent pattern of body-force vectors in the Ishtar Terra region suggests the presence of tensional forces due to the downwelling mantle flow that is responsible for a crustal thickening along the Freyja and Maxwell Montes. Except for the Atla and Beta Regios where the isostasy is relaxed by the (active) mantle plumes, the crustal thickness is spatially highly correlated with the topography, with a thin crust under the plains and a thick crust under the plateaus. The maximum Moho depth under the Maxwell Montes in the Ishtar Terra exceeds 90 km.

Keywords
Crust, Gravity, Mantle, Moho, Body forces, Venus
National Category
Earth and Related Environmental Sciences
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12229 (URN)10.1016/j.pss.2018.03.013 (DOI)000435052100007 ()2-s2.0-85044384729 (Scopus ID)
Note

Available online 24 March 2018

Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2019-05-28Bibliographically approved
Alizadeh-Khameneh, M. A., Eshagh, M. & Jensen, A. O. (2018). Optimization of deformation monitoring networks using finite element strain analysis. Journal of Applied Geodesy, 2(2), 187-197
Open this publication in new window or tab >>Optimization of deformation monitoring networks using finite element strain analysis
2018 (English)In: Journal of Applied Geodesy, ISSN 1862-9016, E-ISSN 1862-9024, Vol. 2, no 2, p. 187-197Article in journal (Refereed) Published
Abstract [en]

An optimal design of a geodetic network can fulfill the requested precision and reliability of the network, and decrease the expenses of its execution by removing unnecessary observations. The role of an optimal design is highlighted in deformation monitoring network due to the repeatability of these networks. The core design problem is how to define precision and reliability criteria. This paper proposes a solution, where the precision criterion is defined based on the precision of deformation parameters, i. e. precision of strain and differential rotations. A strain analysis can be performed to obtain some information about the possible deformation of a deformable object. In this study, we split an area into a number of three-dimensional finite elements with the help of the Delaunay triangulation and performed the strain analysis on each element. According to the obtained precision of deformation parameters in each element, the precision criterion of displacement detection at each network point is then determined. The developed criterion is implemented to optimize the observations from the Global Positioning System (GPS) in Skåne monitoring network in Sweden. The network was established in 1989 and straddled the Tornquist zone, which is one of the most active faults in southern Sweden. The numerical results show that 17 out of all 21 possible GPS baseline observations are sufficient to detect minimum 3 mm displacement at each network point. © 2018 Walter de Gruyter GmbH, Berlin/Boston.

Keywords
Optimization; monitoring networks; GPS; deformation parameters; finite elements; strain analysis
National Category
Earth and Related Environmental Sciences
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12228 (URN)10.1515/jag-2017-0040 (DOI)000428797900005 ()2-s2.0-85045196739 (Scopus ID)
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2019-02-05Bibliographically approved
Seif, M. R., Sharifi, M. A. & Eshagh, M. (2018). Polynomial approximation for fast generation of associated Legendre functions. Acta Geodaetica et Geophysica, 53(2), 275-293
Open this publication in new window or tab >>Polynomial approximation for fast generation of associated Legendre functions
2018 (English)In: Acta Geodaetica et Geophysica, ISSN 2213-5812, Vol. 53, no 2, p. 275-293Article in journal (Refereed) Published
Abstract [en]

Today high-speed computers have simplified many computational problems, but fast techniques and algorithms are still relevant. In this study, the Hermitian polynomial approximation is used for fast evaluation of the associated Legendre functions (ALFs). It has lots of applications in geodesy and geophysics. This method approximates the ALFs instead of computing them by recursive formulae and generate them several times faster. The approximated ALFs by the Newtonian polynomials are compared with Hermitian ones and their differences are discussed. Here, this approach is applied for computing a global geoid model point-wise from EGM08 to degree and order 2160 and in propagating the orbit of a low Earth orbiting satellite. Our numerical results show that the CPU-time decreases at least two times for orbit propagation, and five times for geoid computation comparing to the case where recursive formulae for generation of ALFs are used. The approximation error in the orbit computation is at a sub-millimeter level over two weeks and that the computed geoid 0.01 mm, with a maximum of 1 mm

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Orbits, Approximation errors; Associated Legendre functions; Computational problem; Hermite polynomials; High speed computers; Low earth orbiting satellites; Newton polynomials; Orbit propagation, Polynomial approximation
National Category
Geophysics
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12479 (URN)10.1007/s40328-018-0216-1 (DOI)000445505100007 ()2-s2.0-85047242977 (Scopus ID)
Note

First Online: 28 April 2018

Available from: 2018-06-15 Created: 2018-06-15 Last updated: 2019-05-24Bibliographically approved
Eshagh, M., Ashargie, A. & Bedada, T. B. (2018). Regional recovery of gravity anomaly from the inversion of diagonal components of GOCE gravitational tensor: A Case Study in Ethiopia, Artificial Satellites. Artificial Satellites : he Journal of Space Research Centre of Polish Academy of Sciences, 53(2), 55-74
Open this publication in new window or tab >>Regional recovery of gravity anomaly from the inversion of diagonal components of GOCE gravitational tensor: A Case Study in Ethiopia, Artificial Satellites
2018 (English)In: Artificial Satellites : he Journal of Space Research Centre of Polish Academy of Sciences, E-ISSN 2083-6104, Vol. 53, no 2, p. 55-74Article in journal (Refereed) Published
Abstract [en]

The tensor of gravitation is traceless as the gravitational field of the Earth is harmonic outside the Earth's surface. Therefore, summation of the 2nd-order horizontal derivatives on its diagonal components should be equal to the radial one but with the opposite sign. The gravity field can be recovered locally from either of them, or even their combination. Here, we use the in-orbit diagonal components of the gravitational tensor measured by the gravity field and steady stateocean circulation explorer (GOCE) mission for recovering gravity anomaly with a resolution of 1°×1° at sea level in Ethiopia. In order to solve the system of equations, derived after discretisation of integral equations, the Tikhonov regularisation is applied and the bias of thi sregularisation is estimated and removed from the estimated gravity anomalies. The errors of the anomalies are estimated and their significance of recovery from these diagonal components is investigated. Statistically, the difference between the recovered anomalies from each scenario isnot significant comparing to their errors. However, their joint inversion of the diagonal components improved the solution by about 1 mGal. Furthermore, the inversion processes arebetter stabilised when using errors of the input data compared with its exclusion, but at the penalty of degradation in accuracy of the estimates.

Place, publisher, year, edition, pages
De Gruyter Open, 2018
Keywords
Gravitational field, Laplace condition, Regularisation, error estimation
National Category
Earth and Related Environmental Sciences
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12230 (URN)10.2478/arsa-2018-0006 (DOI)
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2019-03-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0067-8631

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