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  • 51.
    Eshagh, Mehdi
    et al.
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Tenzer, Robert
    University of West Bohemia Plzen,New Technologies for the Information Society (NTIS), Czech Republic.
    Lithospheric stress tensor from gravity and lithospheric structure models2017In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 174, no 7, p. 2677-2688Article in journal (Refereed)
    Abstract [en]

    n this study we investigate the lithospheric stresses computed from the gravity and lithospheric structure models. The functional relation between the lithospheric stress tensor and the gravity field parameters is formulated based on solving the boundary-value problem of elasticity in order to determine the propagation of stresses inside the lithosphere, while assuming the horizontal shear stress components (computed at the base of the lithosphere) as lower boundary values for solving this problem. We further suppress the signature of global mantle flow in the stress spectrum by subtracting the long-wavelength harmonics (below the degree of 13). This numerical scheme is applied to compute the normal and shear stress tensor components globally at the Moho interface. The results reveal that most of the lithospheric stresses are accumulated along active convergent tectonic margins of oceanic subductions and along continent-to-continent tectonic plate collisions. These results indicate that, aside from a frictional drag caused by mantle convection, the largest stresses within the lithosphere are induced by subduction slab pull forces on the side of subducted lithosphere, which are coupled by slightly less pronounced stresses (on the side of overriding lithospheric plate) possibly attributed to trench suction. Our results also show the presence of (intra-plate) lithospheric loading stresses along Hawaii islands. The signature of ridge push (along divergent tectonic margins) and basal shear traction resistive forces is not clearly manifested at the investigated stress spectrum (between the degrees from 13 to 180).

  • 52.
    Eshagh, Mehdi
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Tenzer, Robert
    Wuhan University, China.
    Sub-crustal stress determined using gravity and crust structure models2015In: Computational Geosciences, ISSN 1420-0597, E-ISSN 1573-1499, p. 115-125Article in journal (Refereed)
    Abstract [en]

    The sub-crustal stress induced by mantle convection has been traditionally computed using the Runcorn formulae of solving the Navier-Stokes problem. The main disadvantage of this method is a limited spectral resolution (up to degree 25 of spherical harmonics) due to a divergence of the spherical harmonic expression. To improve the spectral resolution, we propose a new method of computing the horizontal components of the sub-crustal stress based on utilising the stress function with a numerical differentiation. According to the proposed method, the stress function is functionally related to the gravity and crust structure models expressed in terms of spherical harmonics, instead of directly relating the stress components with partial derivatives of these spherical harmonics. The stress components are then computed from the stress function by applying a numerical differentiation. This modification increases the degree-dependent convergence domain of the asymptotically convergent series and consequently allows computing the stress components to a higher spectral resolution, which is compatible with currently available global crustal models. We further utilise the solution to the Vening Meinesz-Moritz inverse problem of isostasy in definition of the stress function. This definition facilitates a variable crustal thickness instead of assuming only a constant value adopted in the Runcorn formulae. The crustal thickness and sub-crustal stress are then determined directly from gravity data and a crustal structure model. We apply this numerical approach to compute the sub-crustal stress globally. Regional results are also presented and discussed over study areas of oceanic subduction zones, convergent continent-to-continent collision zones and hotspots. We demonstrate that the largest (in magnitude) sub-crustal stress occurs mainly along seismically active convergent tectonic plate boundaries.

  • 53.
    Eshagh, Mehdi
    et al.
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Zoghi, Sedigheh
    Division of Geodesy and Satellite Positioning, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Local error calibration of EGM08 geoid using GNSS/levelling data2016In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 130, no July, p. 209-217Article in journal (Refereed)
    Abstract [en]

    The geoid error, computed from EGM08, is unrealistically large due to the continuation of the spherical harmonic coefficient errors down to the surface of the reference ellipsoid. In this study, we try to calibrate such an error by the differences between the EGM08 and GNSS/levelling geoids over Fennoscandia. We use the variance component estimation procedure through combined adjustments of the geoid and GNSS/levelling heights using corrector surfaces of 4-, 5- and 7-parameter. We also develop a simple iterative method to calibrate the geoid error from the a posteriori variance factor and the errors of GNSS/levelling geoid. Our numerical investigations show that performing the separate adjustment and variance component estimation for each country with a two-component stochastic model is more successful than performing it in the whole area with a five-component model. The number of GNSS/levelling data over Sweden and Norway are much larger than those in Denmark and Finland. This causes that the corrector surfaces are fitted better in these countries and consequently the estimated errors for the geoid become larger than what they should be in the others. Based on a 7-parameter corrector surface model, the average error of the EGM08 geoid becomes 12, 17, 51 and 34 mm, in Sweden, Denmark, Norway and Finland, respectively. If the two-component stochastic model is used in a combined adjustment over Fennoscandia this average error will be 48 mm.

  • 54.
    Hussain, Matloob
    et al.
    Earth Sciences department, Quaid-i-Azam University, Islamabad, Pakistan.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Zulfiqar, Ahmed
    Quaid-i-Azam University, Department of Earth Sciences, Islamabad, Pakistan.
    Sadiq, Mohammed
    Quaid-i-Azam University, Department of Earth Sciences, Islamabad, Pakistan.
    Fatolazadeh, Farzam
    K. N. Toosi University of Technology, Department of Geodesy, Iran.
    Changes in gravitational parameters inferred from time-variable GRACE data- A case study for October 2005 Kashmir Earthquake2016In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 132, p. 174-183Article in journal (Refereed)
    Abstract [en]

    The earth's gravity changes are attributed to the redistribution of masses within and/or on the surface of the earth, which are due to the frictional sliding, tensile cracking and/or cataclastic flow of rocks along the faults and detectable by earthquake events. Inversely, the gravity changes are useful to describe the earthquake seismicity over the active orogenic belts. The time variable gravimetric data are hardly available to the public domain. However, Gravity Recovery and Climatic Experiment (GRACE) is the only satellite mission dedicated to model the variation of the gravity field and an available source to the science community. Here, we have tried to envisage gravity changes in terms of gravity anomaly (Δg), geoid (N) and the gravity gradients over the Indo-Pak plate with emphasis upon Kashmir earthquake of October 2005. For this purpose, we engaged the spherical harmonic coefficients of monthly gravity solutions from the GRACE satellite mission, which have good coverage over the entire globe with unprecedented accuracy. We have analysed numerically the solutions after removing the hydrological signals, during August to November 2005, in terms of corresponding monthly differentials of gravity anomaly, geoid and the gradients. The regional structures like Main Mantle Thrust (MMT), Main Karakoram Thrust (MKT), Herat and Chaman faults are in closed association with topography and with gravity parameters from the GRACE gravimetry and EGM2008 model. The monthly differentials of these quantities indicate the stress accumulation in the northeast direction in the study area. Our numerical results show that the horizontal gravity gradients seem to be in good agreement with tectonic boundaries and differentials of the gravitational elements are subtle to the redistribution of rock masses and topography caused by 2005 Kashmir earthquake. Moreover, the gradients are rather more helpful for extracting the coseismic gravity signatures caused by seismicity over the area. Higher positive values of gravity components having higher terrain elevations are more vulnerable to the seismicity and lower risk of diastrophism otherwise.

  • 55.
    Kiamehr, Ramin
    et al.
    Department of Geodesy and Geomatics, Zanjan University, Iran.
    Eshagh, Mehdi
    Royal Institute of Technology, Stockholm, Sweden.
    Estimating variance components of ellipsoidal, orthometric and geoidalheights through the GPS/levelling Network in Iran2008In: Journal of the Earth and Space Physics, Vol. 34, no 3, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The Best Quadratic Unbiased Estimation (BQUE) of variance components in the Gauss-Helmert model is used to combine adjustment of GPS/levelling and geoid to determinethe individual variance components for each of the three height types. Through theresearch, different reasons for achievement of the negative variance components werediscussed and a new modified version of the Best Quadratic Unbiased Non-negativeEstimator (MBQUNE) was successfully developed and applied. This estimation could beuseful for estimating the absolute accuracy level which can be achieved using theGPS/levelling method. A general MATLAB function is presented for numericalestimation of variance components by using the different parametric models. Themodified BQUNE and developed software was successfully applied for estimating thevariance components through the sample GPS/levelling network in Iran. In the followingresearch, we used the 75 outlier free and well distributed GPS/levelling data. Threecorrective surface models based on the 4, 5 and 7 parameter models were used throughthe combined adjustment of the GPS/levelling and geoidal heights. Using the 7-parametermodel, the standard deviation indexes of the geoidal, geodetic and orthometric heights inIran were estimated to be about 27, 39 and 35 cm, respectively.

  • 56.
    Kiamehr, Ramin
    et al.
    Department of Geodesy and Geomatics, Zanjan University, Zanjan, Iran.
    Eshagh, Mehdi
    Division of Geodesy, Royal Institute of Technology, Stockholm.
    Sjöberg, Lars E.
    Division of Geodesy, Royal Institute of Technology, Stockholm.
    Interpretation of the general geophysical patterns of Iran based on the gradient components analysis of the GRACE2008In: Acta Geophysica, ISSN 1895-6572, E-ISSN 1895-7455, Vol. 56, no 2, p. 440-454Article in journal (Refereed)
    Abstract [en]

    Only with satellites it is possible to cover the entire Earth densely with gravityfield related measurements of uniform quality within a short period of time. However,due to the altitude of the satellite orbits, the signals of individual local massesare strongly damped. Based on the approach of Petrovskaya and Vershkov we determinethe gravity gradient tensor directly from the spherical harmonic coefficientsof the recent EIGEN-GL04C combined model of the GRACE satellite mission. Satellitegradiometry can be used as a complementary tool to gravity and geoid informationin interpreting the general geophysical and geodynamical features of theEarth. Due to the high altitude of the satellite, the effects of the topography and theinternal masses of the Earth are strongly damped. However, the gradiometer data,which are nothing else than the second order spatial derivatives of the gravity potential,efficiently counteract signal attenuation at the low and medium frequencies.In this article we review the procedure for estimating the gravity gradientcomponents directly from spherical harmonics coefficients. Then we apply thismethod as a case study for the interpretation of possible geophysical or geodynamicalpatterns in Iran. We found strong correlations between the cross-components ofthe gravity gradient tensor and the components of the deflection of vertical, and weshow that this result agrees with theory. Also, strong correlations of the gravityanomaly, geoid model and a digital elevation model were found with the diagonalelements of the gradient tensor.

  • 57. Norin, Dab
    et al.
    Johansson, Jan M.
    Mårtensson, Stig-Göran
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Natural Sciences and Electrical and Surveying Engineering.
    Geodetic activities in Sweden 2010–20142015Report (Other (popular science, discussion, etc.))
  • 58.
    Novak, Pavel
    et al.
    University of West Bohemia, NTIS–New Technologies for Information Society, Faculty of Applied Sciences, Univerzitní 22, 30614 Plzeň, .
    Tenzer, Robert
    University of Otago, National School of Surveying, Division of Sciences, 310 Castle Street, Dunedin, New Zealand.
    Eshagh, Mehdi
    Royal Institute of Technology, Division of Geodesy and Geoinformatics,.
    Bagherbandi, Mohammad
    Royal Institute of Technology, Division of Geodesy and Geoinformatics,.
    Evaluation of gravitational gradients generated by Earth's crustal structures2013In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 51, p. 22-33Article in journal (Refereed)
    Abstract [en]

    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.

  • 59.
    Nozari, Masoud
    et al.
    Department of Geodesy, K.N. Toosi University of Technology, Tehran, Iran.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Natural Sciences and Electrical and Surveying Engineering. University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    An alternative approach to Eulerian pole determination and unification of velocity fields of tectonic motions2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 617, p. 79-87Article in journal (Refereed)
    Abstract [en]

    One of the methods of unifying the global positioning system (GPS) velocity fields (VFs) of tectonic motions is based on the Eulerian vector (EV) estimation. In this method the difference between each available local VF and a reference VF (REF) is derived and an EV is estimated for the differences in a least-squares sense. After that each local VF is unified with respect to REF using the EV. The classical approach to the EV determination is nonlinear and requires the approximate EV. To solve this problem a simple linear approach is developed in this paper for estimating the EV and applied for unifying the existing local VFs in Iran. Our approach is free of the approximate parameters of the EV, faster and more efficient than the classical one. Here, both of the classical and the new approaches are numerically applied and compared to each other; and used to unify the VFs covering a large part of Iran. The unified velocity field shows an overall northward motion with respect to Eurasia with a convergence pattern around the southern Caspian Basin and a little divergence in the central and southern areas.

  • 60.
    Pitonak, Martin
    et al.
    University of West Bohemia, NTIS—New Technologies for the Information Society, Faculty of Applied Sciences, Technicka´ 8, 306 14 Plzen, Czech Republic.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Sprlak, Michal
    University of Newcastle, School of Engineering, Faculty of Engineering and Built Environment, Callaghan, NSW 2308, Australia.
    Tenzer, Robert
    The Hong Kong Polytechnic University, Department of Land Surveying and Geo-informatics, 181 Chatham Road South, Hung Hom, 999077 Kowloon, Hong Kong.
    Novak, Pavel
    University of West Bohemia, NTIS—New Technologies for the Information Society, Faculty of Applied Sciences, Technicka´ 8, 306 14 Plzen, Czech Republic.
    Spectral combination of spherical gravitational curvature boundary-value problems2018In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 214, no 2, p. 773-791Article in journal (Refereed)
    Abstract [en]

    Four solutions of the spherical gravitational curvature boundary-value problems can be exploited for the determination of the Earth’s gravitational potential. In this paper we discuss the combination of simulated satellite gravitational curvatures, that is, components of the third-order gravitational tensor, by merging these solutions using the spectral combination method. For this purpose, integral estimators of biased-and unbiased-types are derived. In numerical studies, we investigate the performance of the developed mathematical models for the gravitational field modelling in the area of Central Europe based on simulated satellite measurements. First, we verify the correctness of the integral estimators for the spectral downward continuation by a closed-loop test. Estimated errors of the combined solution are about eight orders smaller than those from the individual solutions. Second, we perform a numerical experiment by considering the Gaussian noise with the standard deviation of 6.5 x 10(-17) m(-1) s(-2) in the input data at the satellite altitude of 250 km above the mean Earth sphere. This value of standard deviation is equivalent to a signal-to-noise ratio of 10. Superior results with respect to the global geopotential model TIM-r5 (Brockmann et al. 2014) are obtained by the spectral downward continuation of the vertical-vertical-vertical component with the standard deviation of 2.104 m(2) s(-2), but the root mean square error is the largest and reaches 9.734 m(2) s(-2). Using the spectral combination of all gravitational curvatures the root mean square error is more than 400 times smaller but the standard deviation reaches 17.234 m(2) s(-2). The combination of more components decreases the root mean square error of the corresponding solutions while the standard deviations of the combined solutions do not improve as compared to the solution from the vertical-vertical-vertical component. The presented method represents a weight mean in the spectral domain that minimizes the root mean square error of the combined solutions and improves standard deviation of the solution based only on the least accurate components.

  • 61.
    Rathnayake, Samurdhika
    et al.
    The Hong Kong Polytechnic University, Department of Land Surveying and Geo-Informatics, 181 Chatham Road South, Kowloon, Hong Kong.
    Tenzer, Robert
    The Hong Kong Polytechnic University, Department of Land Surveying and Geo-Informatics, 181 Chatham Road South, Kowloon, Hong Kong.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Pitonak, Martin
    University of West Bohemia, New Technologies for the Information Society, Faculty of Applied Sciences, Technická 8, Pilsen, 306 14, Czech Republic.
    Gravity Maps of the Lithospheric Structure Beneath the Indian Ocean2019In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 40, no 5, p. 1055-1093Article in journal (Refereed)
    Abstract [en]

    The lithospheric structure beneath the Indian Ocean is probably the most complicated, but at the same time, the least understood among world’s oceans. Results of tomographic, geochemical, magnetic and other surveys provide the evidence of its complex geological history. Seismic surveys have been a primary source of information about the lithospheric structure beneath the Indian Ocean, but these experiments are mainly concentrated at locations of a high geophysical interest. Marine gravity data obtained from processing the satellite altimetry measurements, on the other hand, deliver a detailed image of the whole seafloor relief, advancing further the knowledge about its formation, tectonism and volcanism. In this study, we use gravitational, bathymetric, marine sediment and lithospheric density structure data to compile the Bouguer and mantle gravity maps. We then use both gravity maps to interpret the lithospheric structure beneath the Indian Ocean. The Bouguer gravity map reveals major tectonic and volcanic features that are spatially correlated with crustal thickness variations. The mantle gravity map exhibits mainly a thermal signature of the lithospheric mantle. Gravity lows in this gravity map mark distinctively active oceanic divergent tectonic margins along the Central, Southeast and Southwest Indian Ridges including also the Carlsberg Ridge. Gravity lows extend along the Red Sea–Gulf of Aden and East African Rift Systems, confirming a connection between mid-oceanic spreading ridges (in the Indian Ocean) and continental rift systems (in East Africa). The combined interpretation of the Bouguer and mantle gravity maps confirms a non-collisional origin of mountain ranges along continental rift systems in East Africa. The evidence of a southern extension of the East African Rift System and its link with the Southwest Indian Ridge in the mantle gravity map is absent. Similarly, the ongoing breakup of the composite Indo-Australian plate is not manifested. A missing thermal signature in the mantle gravity map at these two locations is explained by the fact that the southern Nubian-Somalian plate boundary (i.e., the Lwandle plate) and the Indo-Australian plate boundary (i.e., the Capricorn plate) are diffuse zones of convergence, characterized by low deformation and seismicity due to very slow rates of relative motions accommodated across these boundaries. The clear manifestation of the thermal signature of intraplate hot spots in the mantle gravity map is also absent. This finding agrees with the evidence from direct heat flow measurements that do not indicate the presence of a significant positive temperature anomaly compared to the oceanic lithosphere of a similar age. © 2019, Springer Nature B.V.

  • 62.
    Romeshkani, Mohsen
    et al.
    Islamic Azad University, Qazvin branch, Qazvin, Iran .
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Deterministically-modified integral estimators of tensor of gravitation2015In: Boletim de Ciências Geodésicas, ISSN 1413-4853, E-ISSN 1982-2170, Vol. 21, no 1, p. 189-212Article in journal (Refereed)
    Abstract [en]

    The Earth's global gravity field modelling is an important subject in Physical Geodesy. For this purpose different satellite gravimetry missions have been designed and launched. Satellite gravity gradiometry (SGG) is a technique to measure the second-order derivatives of the gravity field. The gravity field and steady state ocean circulation explorer (GOCE) is the first satellite mission which uses this technique and is dedicated to recover Earth's gravity models (EGMs) up to medium wavelengths. The existing terrestrial gravimetric data and EGM scan be used for validation of the GOCE data prior to their use. In this research, the tensor of gravitation in the local north-oriented frame is generated using deterministically-modified integral estimators involving terrestrial data and EGMs. The paper presents that the SGG data is assessable with an accuracy of 1-2 mE in Fennoscandia using a modified integral estimatorby the Molodensky method. A degree of modification of 100 and an integration cap size of for integrating terrestrial data are proper parameters for the estimator.

  • 63.
    Seif, M. R.
    et al.
    Arak University of Technology, Department of Surveying Engineering, Arak, Iran.
    Sharifi, M. A.
    University of Tehran, School of Surveying and Geospatial Engineering, College of Engineering, Tehran, Iran.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Polynomial approximation for fast generation of associated Legendre functions2018In: Acta Geodaetica et Geophysica, ISSN 2213-5812, Vol. 53, no 2, p. 275-293Article in journal (Refereed)
    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

  • 64.
    Sjöberg, Lars E.
    et al.
    Royal Institute of Technology (KTH) Division of Geodesy and Geoinformatics.
    Eshagh, Mehdi
    Islamic Azad University, Shahr-e-Rey Branch Department of Surveying Tehran Iran.
    A theory on geoid modeling by spectral combination of data from satellite gravity gradiometry, terrestrial gravity and an Earth gravitational model2012In: Acta Geodaetica et Geophysica Hungarica, ISSN 1217-8977, E-ISSN 1587-1037, Vol. 47, no 1, p. 13-28Article in journal (Refereed)
    Abstract [en]

    In precise geoid modelling the combination of terrestrial gravity data and an Earth Gravitational Model (EGM) is standard. The proper combination of these data sets is of great importance, and spectral combination is one alternative utilized here. In this method data from satellite gravity gradiometry (SGG), terrestrial gravity and an EGM are combined in a least squares sense by minimizing the expected global mean square error. The spectral filtering process also allows the SGG data to be downward continued to the Earth's surface without solving a system of equations, which is likely to be ill-conditioned. Each practical formula is presented as a combination of one or two integral formulas and the harmonic series of the EGM.Numerical studies show that the kernels of the integral part of the geoid and gravity anomaly estimators approach zero at a spherical distance of about 5°. Also shown (by the expected root mean square errors) is the necessity to combine EGM08 with local data, such as terrestrial gravimetric data, and/or SGG data to attain the 1-cm accuracy in local geoid determination.

  • 65.
    Sprlak, Michal
    et al.
    University of West Bohemia, NTIS - New Technologies for the Information Society, Faculty of Applied Sciences, Plzeň, Czech Republic.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Local recovery of sub-crustal stress due to mantle convection from satellite-to-satellite tracking data2016In: Acta Geophysica, ISSN 1895-6572, E-ISSN 1895-7455, Vol. 64, no 4, p. 904-929Article in journal (Refereed)
    Abstract [en]

    Two integral transformations between the stress function, differentiation of which gives the meridian and prime vertical components of the sub-crustal stress due to mantle convection, and the satellite-to-satellite tracking (SST) data are presented in this article. In the first one, the SST data are the disturbing potential differences between twin-satellites and in the second one the line-of-sight (LOS) gravity disturbances. It is shown that the corresponding integral kernels are well-behaving and therefore suitable for inversion and recovery of the stress function from the SST data. Recovery of the stress function and the stress components is also tested in numerical experiments using simulated SST data. Numerical studies over the Himalayas show that inverting the disturbing potential differences leads to a smoother stress function than from inverting LOS gravity disturbances. Application of the presented integral formulae allows for recovery of the stress from the satellite mission GRACE and its planned successor. © 2016 Šprlak and Eshagh.

  • 66.
    Sundararajan, Narasimman
    et al.
    Sultan Qaboos University, Department of Earth Sciences, Muscat, Oman.
    Eshagh, MehdiUniversity West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.Saibi, HakimUnited Arab Emirates University,Abu Dhabi, United Arab Emirates.Meghraoui, MustaphaUniversité de Strasbourg, Strasbourg, France.Al-Garni, MansourKing Abdulaziz University, Jeddah, Saudi Arabia.Giroux, BernardCentre Eau Terre Environnement,Institut National de la Recherche Scientifique, Québec, Canada.
    On Significant Applications of Geophysical Methods: Proceedings of the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 20182019Collection (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

  • 67.
    Tenzer, Robert
    et al.
    Wuhan University, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, Wuhan 430072, Peoples R China.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Natural Sciences and Electrical and Surveying Engineering.
    Global Sub-Crustal Stress Field2016In: Geostatistical and Geospatial Approaches for the Characterization of Natural Resources in the Environment / [ed] Raju, N. Janardhana, Springer International Publishing , 2016, p. 461-465Chapter in book (Other academic)
    Abstract [en]

    The sub-crustal stress has been traditionally computed using the Runcorn's formulae. This method allows computing the stress field only with a very limited spectral resolution. To overcome this problem, we apply a new method of computing the sub-crustal stress components based on utilizing the stress function with a subsequent numerical differentiation. This method increases the (degree-dependent) convergence domain of the asymptotically-convergent series and consequently allows evaluating the stress components to a higher spectral resolution compatible with currently available global crustal models. This method also facilitates the variable Moho geometry, instead of assuming only a constant Moho depth in the Runcorn's formulae. The crustal thickness and the sub-crustal stress are then determined directly from gravity and (seismic) crustal structure models. The numerical result reveals that the largest intensity of the sub-crustal stress occurs mainly along seismically active convergent tectonic plate boundaries, particularly along oceanic subduction zones and continent-to-continent collision zones.

  • 68.
    Tenzer, Robert
    et al.
    Wuhan University, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, Wuhan 430072, Peoples R China..
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    The Sub-Crustal Stress Field in the Taiwan Region2015In: Terrestrial, Atmospheric and Oceanic Science, ISSN 1017-0839, E-ISSN 2223-8964, Vol. 26, no 3, p. 261-268Article in journal (Refereed)
    Abstract [en]

    We investigate the sub-crustal stress in the Taiwan region. A tectonic configuration in this region is dominated by a collision between the Philippine oceanic plate and the Eurasian continental margin. The horizontal components of the sub-crustal stress are computed based on the modified Runcorn’s formulae in terms of the stress function with a subsequent numerical differentiation. This modification increases the (degree-dependent) convergence domain of the asymptotically-convergent series and consequently allows evaluating the stress components to a spectral resolution, which is compatible with currently available global crustal models. Moreover, the solution to the Vening Meinesz-Moritz’s (VMM) inverse isostasy problem is explicitly incorporated in the stress function definition. The sub-crustal stress is then computed for a variable Moho geometry, instead of assuming only a constant Moho depth. The regional results reveal that the Philippine plate subduction underneath the Eurasian continental margin generates the shear sub-crustal stress along the Ryukyu Trench. Some stress anomalies associated with this subduction are also detected along both sides of the Okinawa Trough. A tensional stress along this divergent tectonic plate boundary is attributed to a back-arc rifting. The sub-crustal stress, which is generated by a (reverse) subduction of the Eurasian plate under the Philippine plate, propagates along both sides of the Luzon (volcanic) Arc. This stress field has a prevailing compressional pattern.

  • 69.
    Tenzer, Robert
    et al.
    Wuhan University, The Key Laboratory of Geospace Environment and Geodesy, School of Geodesy and Geomatics,.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Jin, Shuanggen
    Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, China .
    Martian sub-crustal stress from gravity and topographic models2015In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 425, p. 84-92Article in journal (Refereed)
    Abstract [en]

    The latest Martian gravity and topographic models derived from the Mars Orbiter Laser Altimeter and the Mars Global Surveyor spacecraft tracking data are used to compute the sub-crustal stress field on Mars. For this purpose, we apply the method for a simultaneous determination of the horizontal sub-crustal stress component and the crustal thickness based on solving the Navier–Stokes problem and incorporating the Vening Meinesz–Moritz inverse problem of isostasy. Results reveal that most of the Martian sub-crustal stress is concentrated in the Tharsis region, with the most prominent signatures attributed to a formation of Tharsis major volcanoes followed by crustal loading. The stress distribution across the Valles Marineris rift valleys indicates extensional tectonism. This finding agrees with more recent theories of a tectonic origin of Valles Marineris caused, for instance, by a crustal loading of the Tharsis bulge that resulted in a regional trusting and folding. Aside from these features, the Martian stress field is relatively smooth with only a slightly enhanced pattern of major impact basins. The signatures of active global tectonics and polar ice load are absent. Whereas the signature of the hemispheric dichotomy is also missing, the long-wavelength spectrum of the stress field comprises the signature of additional dichotomy attributed to the isostatically uncompensated crustal load of Tharsis volcanic accumulations. These results suggest a different origin of the Earth's and Martian sub-crustal stress. Whereas the former is mainly related to active global tectonics, the latter is generated by a crustal loading and regional tectonism associated with a volcanic evolution on Mars. The additional sub-crustal stress around major impact basins is likely explained by a crustal extrusion after impact followed by a Moho uplift.

  • 70.
    Tenzer, Robert
    et al.
    Wuhan Univ, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, 129 Luoyu Rd, Wuhan 430079, Peoples R China, University of West Bohemia.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Shen, Wenbin
    Wuhan Univ, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, 129 Luoyu Rd, Wuhan 430079, Peoples R China.
    The sub-crustal stress estimation in central Eurasia from gravity, terrain and crustal structure models2017In: Geosciences Journal, ISSN 1226-4806, Vol. 21, no 1, p. 47-54Article in journal (Refereed)
    Abstract [en]

    We investigate the horizontal stress field beneath crustal structures of central Eurasia. The numerical procedure applied for a simultaneous determination of the sub-crustal stress and the crustal thickness from the global gravity, terrain and crustal structure models is based on solving Navier-Stokes' problem which incorporates the inverse solution to the Vening Meinesz- Moritz's problem of isostasy. The numerical results reveal that a spatial distribution of the sub-crustal stress in this study area closely resembles the regional tectonic configuration comprising parts of the Eurasian, Indian and Arabian lithospheric plates. The maximum shear stress intensity is generated by a subduction of the Indian plate beneath the Tibetan block. The intra-plate tectonic configuration is marked by the stress anomalies distributed along major active strike-slip fault systems and sections of subduction which separate the Tibetan and Iranian blocks from the rest of the Eurasian plate. The most pronounced intra-plate stress anomalies are related with a subduction of the Eurasian plate beneath the Tibetan block. We also demonstrate that a prevailing convergent orientation of stress vectors agree with the compressional tectonism of orogenic formations (Himalaya and Tibet Plateau, Than Shan, Zargos and Iranian Plateau), while the extensional tectonism of continental basins (Tarim, Ganges-Brahmaputra, Sichuan) is manifested by a divergence of stress vectors.

  • 71.
    Zampal, Luigi
    et al.
    University of Trieste, Department of Mathematics and Geoscience, Trieste, Italy.
    Tenzer, Robert
    Hong Kong Polytechnic University, Department of Land Surveying and Geo-Informatics, Hong Kong.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Pitonak, Martin
    University of West Bohemia, New Technologies for the Information Society (NTIS), Faculty of Applied Sciences, Czech Republic.
    Evidence of mantle upwelling/downwelling and localized subduction on Venus from the body-force vector analysis2018In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 157, p. 48-62Article in journal (Refereed)
    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.

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