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  • 1. Borradaile, Graham
    et al.
    Almqvist, Bjarne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Correcting distorted paleosecular variation in late glacial lacustrine clay2008In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 166, p. 20-43Article in journal (Refereed)
  • 2.
    Fang, Changming
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Local structure and electronic-spin transition of Fe-bearing MgSiO3 perovskite under conditions of the Earth's lower mantle2008In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 166, no 1-2, p. 77-82Article in journal (Refereed)
    Abstract [en]

    We report first-principles electronic structure calculations on the structural and electronic-spin behaviours of Fe-bearing MgSiO3 crystals up to the pressure of Earth's mantle. The transition pressure of the Fe-bearing MgSiO3 from the orthorhombic perovskite (OPv) to the orthorhombic post-perovskite (OPPv) phase decreases with increasing Fe concentration. The lattice distortion has impacts on the electronic-spin behaviour of the Fe ions in the PVs. The spin-polarizations of the Fe ions in the (Fe,Mg)SiO3 OPvs and OPPvs keep unchanged up to the pressures in the lower mantle. Meanwhile, the Fe-bearing MgSiO3 OPV Containing Fe-Mg-Fe-Si pairs exhibits multiple-magnetic moments co-existing in a large pressure range (from about 78 to 110 GPa), and finally becomes non-magnetic at pressure higher than 110 GPa. These results provide a mechanism to understand the recent experimental results about Fe valence states and the electronic transitions of the Fe-bearing MgSiO3 under high pressure.

  • 3.
    Fang, Chang-Ming
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Structures and stability of ABO(3) orthorhombic perovskites at the Earth's mantle conditions from first-principles theory2006In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 157, no 1-2, p. 1-7Article in journal (Refereed)
    Abstract [en]

    We report first-principles calculations on the structures and stabilities of the ABO(3) (A = Mg and Ca; B = Si and Ge) orthorhombic perovskites (OPvs) under high pressures. Calculations have also been performed for CdGeO3 and CdTiO3 OPvs. The calculations showed that MgSiO3, MgGeO3, CaGeO3, CdGeO3 and CdTiO3 OPvs transform to the orthorhombic post-perovskites (OPPvs) at about 10 1, 47, 55, 78 and 64 GPa, respectively, while CaSiO3 OPv is stable under high pressures. The theoretical results are in good agreement with the available experiments. The lattice distortions with pressure have been studied by analyzing the lattice deviations from the corresponding cubic perovskite (CPv). The lattice distortions increase with pressure for MgSiO3, MgGeO3, CaGeO3 and CdTiO3 OPvs, while CaSiO3 OPv has very small lattice distortions under high-pressures and the lattice distortions of CdGeO3 OPV even decrease with increasing pressure. The OPPvs have large distortions for the a-axis (about -10%).

  • 4.
    Hieronymus, Christoph F.
    Institute of Geophysics, ETH Zürich, Switzerland.
    Time-dependent strain localization in viscous media with state-dependent viscosity2006In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 157, no 3-4, p. 151-163Article in journal (Refereed)
    Abstract [en]

    The temporal evolution of viscous rheologies with dependence on an additional state variable is examined. A localization measure is introduced that quantifies the change in the degree of localization in time. Three sample rheologies are analyzed in detail, each representative of a larger class of rheologies: (1) a grain-size dependent viscosity with grain growth and diminution, (2) shear heating with temperature-dependence according to the Arrhenius law, and (3) shear heating with temperature dependence in the Frank-Kamenetzky approximation. All three rheologies display stages of temporal increase and decrease of localization, depending on the initial conditions. This localization behavior is not discernible in plots of strain rate versus strain at constant driving stress which are the typical output of creep experiments. The grain-size dependence of olivine leads to effectively non-Newtonian behavior with a stress exponent of about 5. If the laws describing the grain-size evolution are applicable to the mantle, then the lower mantle and those parts of the upper mantle that are dominated by diffusion creep thus have a stronger stress-dependence than the depth range governed by dislocation creep, provided that the timescale of deformation is greater than 10^5 –10^6 years.

  • 5.
    Konôpková, Zuzana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology.
    Lazor, Peter
    Uppsala University, Disciplinary Domain of Science and Technology.
    Goncharov, Alexander
    Thermal conductivity in the Earth’s coreIn: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395Article in journal (Other academic)
  • 6.
    Koči, Love
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ab initio calculations of the elastic properties of ferropericlase Mg(1-x)Fe(x)O (x<=0.25)2007In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 164, no 3-4, p. 177-185Article in journal (Refereed)
    Abstract [en]

    Ferropericlase Mg1-xFexO is believed to be the second most abundant mineral in the Earth's mantle. Therefore, the electronic and elastic properties of ferropericlase are important for the understanding of the Earth's interior. Ab initio total energy calculations have been performed for Fe concentrations x ≤ 0.25. The equation of state (EOS) clearly shows a volume expansion as a function of Fe concentration, consistent with experimental data. Magnetic moment calculations as a function of pressure show a high-spin to low-spin transition of Fe2+, and the theoretical transition pressure increases with iron composition. At ambient pressure, we have found that the shear constant C44 reproduces well the experimental data as a function of Fe concentration. The MgO and Mg0.9Fe0.1O minerals show an increasing C44 with pressure, whereas the Δ C44 / Δ P is slightly negative after 26 GPa for Mg0.8Fe0.2O. The C44 softening could be related to the transition from the cubic to a rhombohedrally distorted phase, recently found by experiment.

  • 7. Manaman, Navid Shad
    et al.
    Shomali, Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Upper mantle S-velocity structure and Moho depth variations across Zagros belt, Arabian-Eurasian plate boundary2010In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 180, no 1-2, p. 92-103Article in journal (Refereed)
    Abstract [en]

    The collision of the Arabian and Eurasian plates in the early Miocene, after the subduction of Neo-Tethys ocean beneath Eurasia, formed the Zagros belt, a seismically active continental-continental plate boundary in southwest Iran. The Zagros suture zone is an important seismotectonic boundary indicating an abrupt cutoff between the intense seismicity of the Zagros and the almost aseismic Central Iran plateau. Compared with other more evolved plate boundaries, little is known about the deep lithospheric structure of the Zagros belt, such as the fate of subducted Neo-Tethys plate and ambiguity in the presence of intermediate and deep earthquakes under the Zagros suture zone. In this study, we use the partitioned waveform inversion (PWI) method to image the upper mantle S-velocity structure and Moho depth variations across Zagros collisional zone. The resulting Moho depth along the profile shows the average Moho depth value of order of 40-45 km for most parts of the profile with abrupt crustal thickening in the middle of the profile up to about 65 km. As expected, the derived models show that the relatively old and cold Arabian plate has higher velocity at depth than the younger lithosphere farther north in Central Iran. A sharp and steep subcrustal boundary is found roughly coincident with the surficial expression of the Main Zagros Thrust (MZT), separating two different mantle domains. A high-velocity anomaly, possibly representing a fragment of subducted lithosphere, has been imaged beneath Central Iran at a depth between 350 and 600 km, which is quite similar to the case of Indo-Asian collision in Qinghai-Tibetan plateau. These observations as well as the sudden changes of shallow velocities along the cross-section with a sharp boundary under the Zagros suture zone support the idea that subducted oceanic lithosphere has broken-off under the region of maximum Moho depth. A relatively low velocity region beneath the Arabian plate is also imaged in our high resolution tomography model which is interpreted as an indication of lithospheric delamination within the Arabian lithosphere.

  • 8. Motaghi, K.
    et al.
    Tatar, M.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kaviani, A.
    Priestley, K.
    High resolution image of uppermost mantle beneath NE Iran continental collision zone2012In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 208-209, p. 38-49Article in journal (Refereed)
    Abstract [en]

    We invert 3775 relative P wave arrival times using the ACH damped least square method of Aki et al. (1977) to study upper mantle structure beneath the NE Iran continental collision zone. The data for this study were recorded by 17 three component broad-band stations operated from August 2006 to February 2008 along a profile from the center of Iranian Plateau, near Yazd, to the northeastern part of Iran on the Turan Platform just north of the Kopeh Dagh Mountains. The results confirm the previously known low velocity upper mantle beneath Central Iran. Our tomographic model reveals a deep high velocity anomaly. The surficial expressions of this anomaly are between the Ashkabad and Doruneh Faults, where the resolution and ray coverage are good. A transition zone in uppermost mantle is recognized under the Binalud foreland that we interpreted as suture zone between Iran and Turan platform. Our results indicate that Atrak Valley which is the boundary between the Binalud and Kopeh Dagh Mountains can be considered as the northeastern suture of the Iranian Plateau where Eurasia and Turan Platform under-thrust beneath the Binalud range and Central Iran.

  • 9.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Equation of state (EOS) and collapse of magnetism in iron-rich meteorites at high pressure by first-principles calculations2010In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 182, no 3-4, p. 175-178Article in journal (Refereed)
    Abstract [en]

    We have calculated electronic and structure properties, equation of state (EOS) and collapse of magnetism of different meteoritic materials at high pressure using density functional theory (DFT). The fully optimization structures are obtained by minimization of the total energy and atomic forces of iron-rich materials, which are in good agreement with the experiment. Phase transition of Fe2P (C22 type structure) barringerite into Fe2P (C23 type structure) allabogdanite is calculated to be 26 GPa. Collapse of magnetism (high spin-low spin) of some iron-rich materials are described at various pressures. It has been observed that the optimized equilibrium volume has been changed due to transition of non-magnetic to magnetic material at high pressure, so EOS parameters have also been changed. EOS parameters such as bulk modulus (B-o and derivative of bulk modulus with respect to pressure (B-o') for magnetic and non-magnetic configurations have been calculated by fitting E-V curves with Birch-Murnaghan equation, which confirm the experimental results. (C) 2010 Elsevier B.V. All rights reserved.

  • 10.
    Olsson, Sverker
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Shomali, Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Tomographic inversion of P410s delay times for simultaneous determination of P and S velocities of the upper mantle beneath the Baltic Shield2007In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 160, no 2, p. 157-168Article in journal (Refereed)
    Abstract [en]

    Teleseismic data recorded by stations in the Swedish National Seismic Network (SNSN) are used for a study of upper mantle structure beneath the Baltic Shield using the receiver function technique. The data show very clear conversions from the 410 and 660 km discontinuities. The signals associated with P to S conversions at these discontinuities arrive 1–2 s earlier than predicted by global models such as IASP91 or PREM. We interpret this as a manifestation of higher than average velocities in the mantle beneath the shield, consistent with lower than average global temperatures. For a 1400 km profile along the network, we observe variations of around 1 second in delay times of P410s and slightly less for P660s. Under the assumption that the mantle discontinuities are at a given constant depth, the delay times of the mantle converted phases are tomographically inverted to reveal P and S velocity structure below the stations. Synthetic tests show that this tomographic inversion has the potential to resolve P and S velocity variations at structural scales adequate for upper mantle studies. Results from application to real data appear to be consistent with independently produced mantle velocity structures deduced from normal tomographic arrival time data. For the P velocity model, a north-dipping body of (relatively) low velocity is found for the central part of the profile at 58–64°N. A sharp contrast from low to high velocities that may be associated with the Proterozoic–Archean boundary is found at 66°N.

  • 11.
    Oskooi, Behrooz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Smirnov, Maxim
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Árnason, Knutur
    Eysteinsson, Hjálmar
    Manzella, Adele
    The deep geothermal structure of the Mid-Atlantic Ridge deduced from MT data in SW Iceland2005In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 150, no 1-3, p. 183-195Article in journal (Refereed)
    Abstract [en]

    Iceland is very active tectonically as it is crossed by the Mid-Atlantic Ridge and its associated rift zones and transform faults. The high-temperature geothermal systems are located within the neo-volcanic zone. A detailed comparison of the main features of the resistivity models and well data in exploited geothermal fields has shown that the resistivity structure of Iceland is mainly controlled by alteration mineralogy. In areas where the geothermal circulation and related alteration take place at depths of more than 1.5 km, the investigation depth of the DC and TEM methods is inadequate and the MT method appears to be the most suitable survey method. MT soundings were carried out to determine the deep structure between two neighboring Quaternary geothermal fields: the Hengill volcanic complex and the Brennisteinsfjoll geothermal system, both known as high-temperature systems. MT data were analyzed and modeled using 1D and 2D inversion schemes. Our model of electrical conductivity can be related to secondary mineralization from geothermal fluids. At shallow depths, the resistivity model obtained from the MT data is consistent with the general geoelectrical models of high-temperature geothermal systems in Iceland, as revealed by shallow DC and TEM surveys. The current MT results reveal the presence of an outcropping resistive layer, identified as the typical unaltered porous basalt of the upper crust. This layer is underlain by a highly conductive cap resolved as the smectite–zeolite zone. Below this cap a less conductive zone is identified as the epidote–chlorite zone. A highly conductive material has been recognized in the middle of the profile, at about 5 km depth, and has been interpreted as cooling partial melt representing the main heat source of the geothermal system. This conductor may be connected to the shallow structure through a vertical fault zone located close to the southern edge of the profile.

  • 12. Shirzad, Taghi
    et al.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shallow crustal radial anisotropy beneath the Tehran basin of Iran from seismic ambient noise tomography2014In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 231, p. 16-29Article in journal (Refereed)
    Abstract [en]

    We studied the shear wave velocity structure and radial anisotropy beneath the Tehran basin by analyzing the Rayleigh wave and Love wave empirical Green's functions obtained from cross-correlation of seismic ambient noise. Approximately 199 inter-station Rayleigh and Love wave empirical Green's functions with sufficient signal-to-noise ratios extracted from 30 stations with various sensor types were used for phase velocity dispersion analysis of periods ranging from I to 7 s using an image transformation analysis technique. Dispersion curves extracted from the phase velocity maps were inverted based on non-linear damped least squares inversion method to obtain a quasi-3D model of crustal shear wave velocities. The data used in this study provide an unprecedented opportunity to resolve the spatial distribution of radial anisotropy within the uppermost crust beneath the Tehran basin. The quasi-3D shear wave velocity model obtained in this analysis delineates several distinct low- and high-velocity zones that are generally separated by geological boundaries. High-shear-velocity zones are located primarily around the mountain ranges and extend to depths of 2.0 km, while the low-shear-velocity zone is located near regions with sedimentary layers. In the shallow subsurface, our results indicate strong radial anisotropy with negative magnitude (Vsv > VsH) primarily associated with thick sedimentary deposits, reflecting vertical alignment of cracks. With increasing depth, the magnitude of the radial anisotropy shifts from predominantly negative (less than - 10%) to predominantly positive (greater than 5%). Our results show a distinct change in radial anisotropy between the uppermost sedimentary layer and the bedrock.

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