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  • 1
    Monograph available for loan
    Monograph available for loan
    Global dynamics of the earth : applications of normal mode relaxation theory to solid-earth geophysics (2004)
    Dordrecht [u.a.] : Kluwer
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    Call number: 5/M 04.0221
    In: Modern approaches in geophysics
    Type of Medium: Monograph available for loan
    Pages: xiv, 328 S.
    ISBN: 1402012675
    Series Statement: Modern approaches in geophysics 20
    Location: Reading room
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    On A Particular Solution of the Non-Linear Liouville Equations (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 114 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The rotational behaviour of a stratified viscoelastic planet is analysed by means of a quasi-analytical method. Our approach is particularly appropriate to study the long-term polar wander induced by internal loads, and in particular to study the effects due to time-dependent mantle convection. We focus on a simple explicit solution of the Liouville non-linear equations, in order to establish the relationships between internal rheological constitution of the planet and polar motion. Both the rate and the direction of polar wander are found to be extremely sensitive to the mantle stratification and in particular to the nature of the 670km depth seismic discontinuity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb03927.x
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  • 3
    Electronic Resource
    Electronic Resource
    Effects on post-glacial rebound from the hard rheology in the transition zone (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 109 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We analyse the influences of a viscosity increase in the transition zone between 420 and 670 km on the geophysical signatures induced by post-glacial rebound, ranging from the perturbations in the Earth's rotation to the short wavelength features associated with the migration of the peripheral bulge. A self-gravitating model is adopted, consisting of an elastic lithosphere, a three-layer viscoelastic mantle and an inviscid core.The horizontal displacements and velocities and the stress pattern are extremely sensitive to the viscosity increase and to the chemical stratification of the transition zone. The hardening of the upper and the chemical density jumps in mantle below the 420 discontinuity induces a channel effect which contaminates the horizontal deformation both in the near-field and in the far-field from the ice-sheets. These findings indicate that intraplate geodetic data can be used to put bounds on the viscosity increase in the transition zone and on the amount of chemical stratification in the mantle.The stress field induced in the lithosphere by the Pleistocenic ice-sheet disintegration is a very sensitive function of mantle viscosity stratification. The existence of seismic activity along passive continental margins of previously glaciated areas requires a substantial viscosity increase in the mantle, with the viscosity of the transition zone acting as a controlling parameter. A viscously stratified mantle is responsible for a delayed upward migration of stress in the lithosphere which can account for the seismicity today.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00125.x
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  • 4
    Electronic Resource
    Electronic Resource
    Polar wandering of a dynamic earth (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 113 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The rotational behaviour of a stratified visco-elastic planet submitted to changes in its inertia tensor is studied in a viscous quasi-fluid approximation. This approximation allows for large displacements of the Earth rotation axis with respect to the entire mantle but is only valid for mass redistribution within the planet occurring on the time scale of a few million years. Such a motion, called true polar wander (TPW), is detected by palaeomagneticiens assuming that the Earth's magnetic field remains on average aligned with the spin axis. Our model shows that a downgoing cold slab induces a TPW which quickly brings this slab to the pole for a mantle of uniform viscosity. The same slab is slowly moved toward the equator when a large viscosity increase with depth takes place in the mantle. Our model is also suitable to investigate the effects of a non-steady-state convection on the Earth's rotation. We discuss these effects using a simple mass redistribution model inspired by the pioneering paper of Goldreich & Toomre (1969). It consists of studying the TPW induced by a random distribution of slabs sinking into the mantle. For such a mass redistribution, only a strongly stratified mantle can reduce the Earth's pole velocity below 1d̀ Ma-1, which is the upper bound value observed by palaeomagnetic investigations for the last 200 Ma. Our model also shows that when corrected for the hydrostatic flattening, the Earth's polar inertia generally corresponds to the maximum inertia, as it is presently observed. However, this may not be the case during some short time periods. We also discuss the amount of excess polar flattening that can be related to tidal deceleration. This frozen component is found to be negligible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb00888.x
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  • 5
    Electronic Resource
    Electronic Resource
    Geobal post-seismic deformation (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 120 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We quantify the effects of post-seismic deformation on the radial and horizontal components of the displacement, in the near- and far-field of strike- and dip-slip point dislocations; these sources are embedded in the elastic top layer of a spherical, self-gravitating, stratified viscoelastic earth. Within the scheme of the normal mode technique, we derive the explicit analytical expression of the fundamental matrix for the toroidal component of the field equations; this component is propagated, together with its spheroidal counterpart, from the core-mantle boundary to the earth's surface. Viscosity stratification at 670km depth influences the radial and horizontal deformation accompanying viscoelastic relaxation in the mantle over time-scales of 103-104 yr, both in the near-field, ranging from 100 to 500 km and in the far-field, from 103 to 5 X 103 km. If the upper mantle is differentiated into a low-viscosity zone beneath the lithosphere and a normal upper mantle, faster relaxation is obtained. For an asthenospheric viscosity of 1020 Pa s we obtain, for a strike-slip dislocation and a seismic moment of 1022 N m characteristic of an average large earthquake, horizontal rates of 1-4 mm yr-1 in the near-field and 0.05-0.4 mm yr-1 in the far-field; these values are maintained over time-scales of 10-103 yr. Larger rates, with shorter duration, are obtained if the viscosity is reduced in the low-viscosity channel. As expected, strike-slip dislocations are the most effective in driving horizontal deformation in the far-field in comparison with dip-slip ones. It is noteworthy that horizontal velocities are maintained longer in the far-field in comparison with radial ones, which is not surprising since momentum is propagated in far regions essentially in the horizontal direction; radial deformation is generally lower in the far-field. VLBI techniques, with a precision of a few parts per billion over distances of 103 km, can detect global post-seismic deformation induced by large earthquakes. Our results affect the interpretation of the transfer of stress and seismic activity among different plate boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb01838.x
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  • 6
    Electronic Resource
    Electronic Resource
    Mantle Rheology, Viscomagnetic Coupling At the Core-Mantle Boundary and Differential Rotation of the Core Induced By Pleistocenic Deglaciation (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 117 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The influence of the viscomagnetic coupling at the core-mantle boundary (CMB) on the differential rotation of the core and non-tidal acceleration induced by the Pleistocenic deglaciation is investigated for stratified mantle models with steady-state or transient rheologies. For a realistic modelling of the viscomagnetic coupling, the time-dependent viscoelastic topography at the CMB induces a westward drift of the core with respect to the mantle that can be correlated to the zonal component of the secular drift of the geomagnetic field. Starting from a reference model based on the Maxwell rheology and a viscosity profile inferred from j2 data and non-tidal acceleration, with 1021 Pa s and 5 × 1021 Pa s for upper and lower mantle respectively, we study first the effects of the hardening of the upper mantle in the transition zone between 420 and 670 km depth. This hardening is responsible for a 30 per cent reduction in the westward drift with respect to a uniform upper mantle. the impact of a viscosity decrease on the top of the lower mantle is considered next. the softening of the lower mantle beneath the 670 km discontinuity counteracts the effects of the transition zone, enhancing the differential rotation of the core. the D″ layer is also implemented in order to analyse the influence of the decoupling at the bottom of the mantle, responsible for faster relaxation of the topography. If lower mantle viscosity is increased beyond the threshold of 1022 Pas we obtain a differential rotation of the core in the opposite direction or an eastward drift. We also analyse the impact of a Burgers rheology for the lower mantle to simulate transient effects. For this rheology, steady-state viscosities in the lower mantle higher than 1022 Pas, in agreement with estimates from long-wavelength geoid anomalies and recent findings from true polar wander, allow a westward drift of the core.Non-tidal acceleration is generally less affected by rheological variations than the differential rotation. Changes in the non-tidal acceleration induced by the various rheological models are, on the other hand, comparable with the error bounds in the observed values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb03300.x
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamic models of subduction: geophysical and geological evidence in the Tyrrhenian Sea (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Predictions based on a 2-D finite-element model for subduction underneath the Calabrian Arc in southern Italy are compared with a variety of geophysical and geological data, such as the present-day stress pattern within the slab, uplift from the elevation of marine terraces in Calabria and subsidence in the Tyrrhenian Marsili Basin from ODP Leg 107. We model the behaviour of the slab driven by slab pull, in agreement with the present tectonic style in this part of the Mediterranean as suggested by several investigators. The model accounts for the crustal, lithospheric and mantle structures in a vertical cross-section perpendicular to the Calabrian subduction zone. The shape of the slab is constrained on the basis of new tomographic images in the southern Tyrrhenian Sea, which were obtained from the regional seismic stations of the Istituto Nazionale di Geofisica, while the rheological properties of the mantle are taken from global dynamic models. Density contrasts between the subducted slab and the surrounding mantle, based on petrological models, drive the flow in our viscoelastic model; stress values, displacements and vertical velocities at the surface are sampled at different times after loading until dynamic equilibrium is reached. Our estimates are appropriate for a time window of 100 kyr; the validity of our comparison with the geological record is based on the assumption that the tectonic configuration in the past was not substantially different from that of the present day. Two families of models, with unlocked and locked subduction faults, are considered. The unlocked models allow for roll-back of the trench of about 20 mm yr−1, in agreement with some geological estimates; the same family of models predicts uplift of the Calabrian Arc of about 1 mm yr−1 and subsidence in the Marsili Basin of 1–2 mm yr−1, in agreement with geological surveys. The deviatoric stress obtained from the unlocked model is consistent with the continuous distribution of deep seismicity in the southern Tyrrhenian Sea, with minor concentration within the lithospheric wedge. Locked models fail to reproduce these geophysical and geological observations. Predictions derived from a detached slab model are not consistent with the continuous hypocentral distribution of deep seismicity in the southern Tyrrhenian Sea. Deformation at the surface and the stress patterns at depth for a detached slab differ substantially from those of a continuous plate: dynamic topography and horizontal motions are reduced, when compared with the continuous plate, with deviatoric stresses concentrated within the relict slab. Our results indicate that subduction is a major tectonic process in the southern Tyrrhenian Sea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb05310.x
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  • 8
    Electronic Resource
    Electronic Resource
    Lateral heterogeneities in mantle viscosity and post-glacial rebound (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 98 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Seismic tomographic results and convection calculations support the evidence of horizontal temperature variations in the mantle. On the basis of commonly accepted rheological laws, we thus expect lateral variations in the viscosity of several orders of magnitude. This paper is concerned with the effects of lateral viscosity variations on vertical displacement induced by Pleistocenic deglaciation. A finite-element scheme in axial symmetry mimics the relaxation process of a flat Earth model characterized by a linear Maxwell rheology. We follow a spectral approach to analyse the impact of lateral viscosity variations with different amplitudes and wavelengths. The potential impact of lithospheric thickening and viscosity increase in stable continental regions on the interpretation of sea level data is also analysed.Lateral viscosity heterogeneities are found to have strong influence on ground deformations induced in deglaciated areas. From the analysis of sea level data near the centre of the former Fennoscandian ice sheet and the theoretical predictions of radially and laterally stratified Earth models, we explore the extent to which lateral viscosity contrasts may have influenced the inference of long-term mantle viscosity.While radially stratified models predict a rather uniform mantle viscosity, we show that lateral viscosity contrasts of 1 or 2 orders of magnitude are consistent with sea level data if the wavelength of the heterogeneity is comparable with the dimension of a convecting cell. In this case, the average viscosity can deviate by around an order of magnitude from the ‘canonical’ value of 1021 Pa s predicted by rebound models in the past. Viscosity values close to 1021 Pa s are found to be appropriate for the mantle region underlying the load. Long wavelength viscosity variations of 3 or 4 orders of magnitude degrade our ability to reproduce the observed uplift in the centre of the ice sheet and must be ruled out.For wavelengths comparable with the horizontal extension of the surface load and viscosity contrasts of 1 or 2 orders of magnitude, model results are found to be inconsistent with sea level data. These findings suggest that rebound modelling can become a useful tool to constrain the magnitude and wavelength of viscosity contrasts.Comparison between horizontally and vertically varying models indicates that lateral viscosity heterogeneities could have been interpreted as radial variations in previous rebound studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb02279.x
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  • 9
    Electronic Resource
    Electronic Resource
    Excitation of true polar wander by subduction (1992)
    [s.l.] : Nature Publishing Group
    Nature 360 (1992), S. 452-454 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The 1969 paper of Goldreich and Toomre11 renewed the interest of the geophysical community12 in the role of polar wandering in Earth's dynamics. Their example of a colony of beetles crawling on the surface of a quasi-rigid Earth suggests that large excursions of the axis of rotation with respect to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/360452a0
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  • 10
    Electronic Resource
    Electronic Resource
    Interaction of cryospheric forcings with rotational dynamics has consequences for ice ages (1982)
    [s.l.] : Nature Publishing Group
    Nature 296 (1982), S. 338-341 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In the past decade there has been an increasing number of observations4'7 based on the correlation between the periodicities of the Earth's orbit and the time series analyses of the oxygen isotope data to suggest that there is a cause and effect relationship between the two systems. Nonetheless, it ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/296338a0
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