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  • 1
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    In:  Earth planet. Sci. Lett., Tulsa, 3-4, vol. 245, no. 1-2, pp. 359-364, pp. B09405, (ISBN: 0-12-018847-3)
    Publication Date: 2006
    Keywords: Subduction zone ; Rheology ; Stress ; Plate tectonics ; ConvolutionE ; EPSL ; plate ; motions ; mantle ; convection ; rheology ; of ; lithosphere
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  • 2
    Publication Date: 2015-05-07
    Description: Subducting plate (SP) curvature exerts a key control on the amount of bending dissipation associated with subduction, and the magnitude of the subduction resisting bending force. However, the factors controlling the development of SP curvature are not well understood. We use numerical models to quantify the role of SP rheology on the minimum radius of curvature, R min . We find that R min depends strongly on the SP thickness when the rheology is viscous. This dependence is substantially reduced when the SP behaves plastically, in line with the lack of correlation between R min and SP thickness on Earth. In contrast, plasticity leads to a strong positive correlation between R min and the overriding plate (OP) thickness. Using an analysis of R min vs. OP thickness, we show that such a positive correlation exists on Earth. This suggests that OP structure, in conjunction with SP plasticity, is crucial in generating slab curvature systematics on Earth.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2013-01-18
    Description: Concentrations of cosmogenic iodine, 129 I, in the pore fluid of marine sediments often indicate that the pore fluid is much older than the host sediment, even when vertical flow due to sediment compaction is taken into account. Old pore fluid has been used in previous studies to argue for pervasive upward fluid flow and a deep methane source for hydrate deposits. Alternatively, old pore fluid age may reflect more complex flow patterns. We use a two-dimensional numerical transport model to account for the effects of topography and fractures on pore fluid pathlines when sediment permeability is anisotropic. We find that fluid focusing can cause significant lateral migration as well as regions where downward flow reverses direction and returns toward the seafloor. Longer pathlines can produce pore fluid ages much older than that expected with a one-dimensional compaction model. For steady-state models with geometry representative of Blake Ridge (USA), a well-studied hydrate province, we find pore fluid ages beneath regions of topography and within fractured zones that are up to 70 Ma old. Our results suggest that the measurements of 129 I/ 127 I reflect a mixture of new and old pore fluid. However, old pore fluid need not originate at great depths. Methane within pore fluids can travel laterally several kilometers, implying an extensive source region around the deposit. This type of focusing should aid hydrate formation beneath topographic highs. © 2013 American Geophysical Union. All rights reserved
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2016-02-28
    Description: Submarine groundwater discharge (SGD) is a large-scale, buoyancy-driven, offshore flow of terrestrial groundwater. If SGD occurs within the permafrost-bearing sediments of the circum-Arctic shelf, such fluid circulation may transport large amounts of dissolved methane to the circum-Arctic shelf, aiding the formation of permafrost-associated gas hydrate. We investigate the feasibility of this new permafrost-associated gas hydrate formation mechanism with a 2D, multi-phase fluid flow model, using the Canadian Beaufort Shelf as an example. The numerical model includes freeze/thaw permafrost processes and predicts the unsteady, 2D methane solubility field for hydrate inventory calculations. Model results show that widespread, low-saturation hydrate deposits accumulate within and below submarine permafrost, even if offshore-flowing groundwater is under-saturated in methane gas. While intra-permafrost hydrate inventory varies widely depending on permafrost extent, sub-permafrost hydrate stability remains largely intact across consecutive glacial cycles, allowing widespread sub-permafrost accumulation over time. Methane gas escape to the sediment surface (atmosphere) is predicted along the seaward permafrost boundary during the early to middle years of each glacial epoch; however, if free gas is trapped within the forming permafrost layer instead, venting may be delayed until ocean transgression deepens the permafrost table during interglacial periods, and may be related to the spatial distribution of observed pingo-like features (PLFs) on the Canadian Beaufort Shelf. Shallow, gas charged sediments are predicted above the gas hydrate stability zone at the mid-shelf to shelf edge and the upper slope, where a gap in hydrate stability allows free gas to accumulate and numerous PLFs have been observed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2011-07-22
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2011-04-30
    Description: Upward fluid flow is often invoked to explain the occurrence of methane hydrate in ocean sediments, whereas one-dimensional compaction models predict downward flow relative to the seafloor. Explaining the presence of upward flow requires a more complete compaction model. We develop a two-dimensional model of compaction-driven flow to quantify the focusing of pore fluids by topography and fractures when sediments have anisotropic permeability. We use a bulk anisotropic permeability to capture the effects of lithologic layering when the grid spacing is too coarse to resolve individual layers. Even small slopes (10°) in bedding planes produce upward fluid velocity, with focusing becoming more effective as slopes increase. Additionally, focusing causes high excess pore pressure to develop below topographic highs, promoting high-angle fracturing near the crest. Magnitudes of upward pore fluid velocity are much larger in fractured zones, particularly when the surrounding sediment matrix is anisotropic in permeability. Enhanced flow of methane-bearing fluids from depth provides a simple explanation for preferential accumulation of hydrate under topographic highs.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2016-02-13
    Description: Numerical simulations of the geodynamo have successfully represented many observable characteristics of the geomagnetic field, yielding insight into the fundamental processes that generate magnetic fields in the Earth's core. Because of limited spatial resolution, however, the diffusivities in numerical dynamo models are much larger than those in the Earth's core, and consequently, questions remain about how realistic these models are. The typical strategy used to address this issue has been to continue to increase the resolution of these quasi-laminar models with increasing computational resources, thus pushing them toward more realistic parameter regimes. We assess which methods are most promising for the next generation of supercomputers, which will offer access to O (10 6 ) processor cores for large problems. Here we report performance and accuracy benchmarks from 15 dynamo codes that employ a range of numerical and parallelization methods. Computational performance is assessed on the basis of weak and strong scaling behavior up to 16,384 processor cores. Extrapolations of our weak scaling results indicate that dynamo codes that employ two- or three-dimensional domain decompositions can perform efficiently on up to ∼10 6 processor cores, paving the way for more realistic simulations in the next model generation. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 388 (1997), S. 571-573 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Recent seismological studies, have suggested that the inner core is rotating relative to the bulk of the Earth, a situation which (according to numerical simulations) may be sustained by convective flow in the liquid outer core. On the other hand, large gravitational forces due to the ...
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 120 (1995), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We calculate the magnetic perturbation that occurs near the inner core boundary when the conducting materials on either side of the boundary are displaced by translational oscillations of the inner core. The associated Lorentz forces and ohmic losses cause changes in the period and damping of the oscillations which may be detectable in gravity measurements. Estimates of these changes depend on the average value of the radial main field B̄r near the inner core boundary. The value of B̄r also affects the character of the magnetic disturbance in the fluid core. For B̄r 〈 0.002 T, the magnetic perturbation at the inner core boundary propagates into the overlying fluid core by diffusion, while for B̄r 〉0.002T the perturbation is transmitted by Alfven waves. The most observable effects are associated with the damping of the oscillations. Typical values of the damping factor Q vary widely with B̄r, but may be as low as 2000. Since Q is extremely sensitive to the main magnetic field we suggest that observations of the inner core oscillations might be used to infer the average strength of the field near the inner core boundary. To facilitate the interpretation of the gravity measurements, we present analytical expressions for the effect of a magnetic field on the period and Q of inner core oscillations.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A spectral method of solving boundary-layer problems is presented. The method uses Laguerre polynomials to construct orthogonal basis functions that satisfy far-field conditions automatically. An implementation of the method is outlined and two illustrative examples are presented. Both examples have known solutions, which are used to test the accuracy and computational efficiency of the method. Useful estimates of the numerical error are obtained and a strategy is developed to adjust the basis functions in order to optimize the rate of convergence.
    Type of Medium: Electronic Resource
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