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  • 1
    Electronic Resource
    Electronic Resource
    Effects of rigidity layering, gravity and stress relaxation on 3-D subsurface fault displacement fields (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 118 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Elastic dislocation theory has been modified to determine 3-D subsurface displacements for faults in a three-layer elastic-gravitational medium. A new set of kernel functions for Fourier-Bessel integrals describing subsurface displacements have been derived, using the Thomson-Haskell propagator matrix technique, and has been used to investigate the effect of layering and gravity on subsurface displacement fields. Within our three-layer model, layer 1 may be used to represent the seismogenic upper crust, layer 2 the ductile lower crust and layer 3 the ductile mantle.For a point source within the upper layer, lower layer rigidity moduli control the amplitude and wavelength of displacements within the upper layer and the relative distribution of uplift and subsidence within foot and hanging wall. Displacement variations, due to lower layer rigidity moduli changes, increase with depth and are profound at the base of the upper layer and within the lower layers. High-rigidity-moduli lower layers attenuate the upper layer displacement field, while a decrease gives amplification. The effect of gravity on the subsurface displacement field is more pronounced when the rigidity of the lower layers is small.The elastic-gravitational dislocation model has been used to examine co-seismic and post-seismic components of surface and subsurface displacement during extension of continental lithosphere. The model predicts surface co-seismic footwall uplift and hanging-wall subsidence; the co-seismic subsidence being greater than the uplift. Post-seismic relaxation of stress within the lower crust and mantle by post-seismic ductile deformation, gives an increase in footwall uplift and a decrease in maximum hanging-wall subsidence within the upper layer. A decrease in upper layer rigidity due to post-seismic brittle or plastic deformation within the upper crust leads to a decrease in the wavelength of surface footwall uplift and hanging-wall subsidence. The elastic-gravitational dislocation model has also been used to investigate the development of Moho topography during continental extension. Co-seismically Moho under footwall is predicted to uplift, while that under hanging wall subsides but by a smaller magnitude. During post-seismic relaxation Moho topography is predicted at first to increase in magnitude and then to decay. The existence of preserved Moho topography uplift associated with old continental rifts implies a finite long-term ductile strength within the lower crust and mantle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb04684.x
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  • 2
    Electronic Resource
    Electronic Resource
    3-D subsurface displacement and strain fields for faults and fault arrays in a layered elastic half-space (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 111 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A quantitative model using elastic dislocation theory has been developed to model the near-field subsurface displacement field associated with faults and fault arrays within an elastic layer above an elastic half-space. A fault is modelled as a surface across which there is a discontinuity in prescribed displacements. Fault displacements may be oblique as well as dip-slip. The mathematical expressions for the surface and subsurface displacements are formed using the Thomson-Haskell matrix technique. Faults may intersect the free surface or may be blind. The model has been used to determine the 3-D surface and subsurface displacement fields for a rectangular fault with constant slip and for an elliptical fault on which the slip varies from a point of maximum displacement at the centre to zero displacement at an elliptical tip-line. The 3-D displacement field and associated strain tensor may be determined for individual slip events on a fault or for cumulative fault displacements. Displacement contour maps may be constructed for either originally horizontal, vertical or inclined horizons. The model has also been applied to multiple fault arrays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb02111.x
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Intraplate lithosphere strength and heat flow (1982)
    [s.l.] : Nature Publishing Group
    Nature 299 (1982), S. 540-542 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A fundamental property of normal intraplate lithosphere is that it exhibits no significant internal lateral distortion over time periods of the order of tens or hundreds of Myr as testified, for example, by the exactness of fit of the passive continental margins across the Atlantic1. This lack of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/299540a0
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  • 4
    Electronic Resource
    Electronic Resource
    Coseismic and postseismic subsurface displacements and strains for a vertical strike-slip fault in a three-layer elastic medium (1994)
    Springer
    Pure and applied geophysics 142 (1994), S. 687-709 
    Details
    ISSN: 1420-9136
    Keywords: Strike-slip faulting ; earthquakes ; subsurface displacement and strain ; coseismic ; postseismic ; elastic dislocation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A three-layer elastic-gravitational fault displacement model using dislocation theory has been developed and used to examine the effect of layering of earth elastic moduli on surface and subsurface displacement fields for a vertical strike-slip fault. The model has been used to examine the effect of depth variation of elastic properties at coseismic and postseismic time scales. For pure strike-slip motion the effect of gravity on coseismic and postseismic horizontal deformation is negligible. For coseismic deformation the model predicts that (for constant Poisson's ratio) an increase in elastic moduli with depth attenuates the displacements within the upper layers with respect to displacement distribution for a uniform half-space, while an inclusion of a soft layer between the top layer and lower half-space amplifies upper layer displacements. The effect of variation in Poisson's ratio on surface and subsurface displacements has also been examined. The effect of postseismic stress relaxation on surface and subsurface displacements for a three-layer model has been calculated and compared with that of a uniformly relaxed half-space model. Layer 1 is assumed to correspond to the upper crust, layer 2 the lower crust and layer 3 the upper mantle. The effect of postseismic stress relaxation within a uniform half-space and within just the lower crust and upper mantle has been examined. Stress relaxation within the whole half-space decreases the amplitude and shortens the wavelength of displacements, while stress relaxation within the lower two layers increases the amplitude and broadens the wavelength of displacements. The difference between uniform and layered postseismic relaxation is particularly pronounced at the base of the crust. Coseismic and postseismic normal and volumetric strains for a vertical strike-slip fault have also been examined. For a uniformly relaxed half-space model, an increase in normal strains is shown with respect to the coseismic elastic solution, whereas the postseismic volumetric strain is effectively zero. For a three-layer model with stress relaxation in the lower layers only, the normal and volumetric strains within the top elastic layer resemble coseismic strains, while in the lower layers which suffer a rigidity decrease, the postseismic volumetric strain is effectively zero.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876060
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  • 5
    Electronic Resource
    Electronic Resource
    Use of synthetic fracture logs derived from borehole geophysics to assess mine roof and floor quality (1983)
    Springer
    Geotechnical and geological engineering 1 (1983), S. 253-260 
    Details
    ISSN: 1573-1529
    Keywords: Coal mining ; geophysics ; borehole log
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Conclusion Geotechnical and lithology data can be reliably derived from borehole geophysical logs. The advantages of deriving geotechnical and lithology data directly from geophysical logs rather than from core examination is that the produced data is continuous, readily interpretable and consistent. In addition the technique is labour saving and cost cutting, especially since data may be extracted from cheaper rock-bitted boreholes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00881615
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  • 6
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    Evidence for magma entrapment below oceanic crust from deep seismic reflections in the Western Somali Basin (2016)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2016-05-24
    Description: Our understanding of melt generation, migration, and extraction in the Earth’s mantle beneath mid-oceanic ridges is mostly derived from geodynamic numerical models constrained by geological and geophysical observations at sea and field investigations of ophiolites, and is therefore restricted to the oceanic crust and the shallow part of the mantle. Here we use a 〉200-km-long, deep seismic reflection section to image with high resolution the sub-oceanic lithosphere within the Western Somali Basin (offshore eastern Africa) where spreading ceased at ca. 120 Ma. The location of the failed spreading axis is inferred from both seismic data and gravity data. Several groups of strong reflections are imaged to depths of 〉30 km below the top of the oceanic crust. We interpret the deepest reflectors, within the mantle, as resulting from frozen melt bodies which may be relicts of a paleo–melt channel system located at the base of the lithosphere and formerly feeding the failed ridge axis. Other reflectors within the mantle may correspond to melt bodies injected into major shear zones along the Davie fracture zone. Another group of reflectors, located below a 8–5-km-thick oceanic crust, is interpreted as marking a fossil melt-rich crust-mantle transition zone as much as 3 km thick. This interpretation implies an inefficient extraction of melt out of the mantle, which is favored by the combination of a slow spreading rate and a high magma budget.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 7
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    The palaeo-bathymetry of base Aptian salt deposition on the northern Angolan rifted margin: constraints from flexural back-stripping and reverse post-break-up thermal subsidence modelling (2016)
    Geological Society of London
    Details
    Publication Date: 2016-04-15
    Description: The bathymetric datum with respect to global sea level for Aptian salt deposition in the South Atlantic is hotly debated. Some models propose that the salt was deposited in an isolated ocean basin in which local sea level was between 2 and 3 km below the global level. In this study, we use reverse post-break-up subsidence modelling to determine the palaeo-bathymetry of base Aptian salt deposition on the Angolan rifted continental margin. The reverse post-break-up subsidence modelling consists of the sequential flexural isostatic back-stripping of the post-break-up sedimentary sequences, decompaction of remaining sedimentary units and reverse modelling of post-break-up lithosphere thermal subsidence. The reverse modelling of post-break-up lithosphere thermal subsidence is carried out in 2D and requires knowledge of the continental lithosphere stretching factor (β), which is determined from gravity anomaly inversion. The analysis has been applied to the ION-GXT CS1-2400 deep long-offset seismic reflection profile, and two seismic cross-sections (P3 and P7+11) from offshore northern Angola. Reverse post-break-up subsidence modelling restores the proximal autochthonous base salt to between 0.2 and 0.6 km below global sea level at the time of break-up. In contrast, the predicted water-loaded bathymetries of the more distal base salt restored to break-up time are much greater between 2 and 3 km. The predicted bathymetries of the first unequivocal oceanic crust at break-up are approximately 2.5 km, as expected for newly formed oceanic crust of ‘normal’ thickness. Several interpretations of these results are possible. Our preferred interpretation is that all Aptian salt on the northern Angola rifted continental margin was deposited between 0.2 and 0.6 km beneath global sea level, and that the proximal salt subsided by post-rift (post-tectonic) thermal subsidence alone; while the distal salt formed during late syn-rift, when the underlying crust was actively thinning, resulting in additional tectonic subsidence (followed by post-rift thermal subsidence). An alternative interpretation is that the distal salt is para-autochthonous and moved downslope into much deeper water during and just after break-up. We do not believe that a deep isolated ocean basin, with a local sea level 2–3 km beneath that of the global sea level, as has been proposed, is required to explain the Aptian salt deposition on the northern Angolan rifted continental margin.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Geological Society of London
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  • 8
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    Spatial and temporal evolution of hyperextended rift systems: Implication for the nature, kinematics, and timing of the Iberian-European plate boundary (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-01-01
    Description: We focus on the Iberian-European plate boundary (IEPB), whose nature, age, and evolution are strongly debated. In contrast to previous interpretations of the IEPB as a major lithospheric-scale left-lateral strike-slip fault, we propose a more complex deformation history. The mapping of rift domains at the transition between Iberia and Europe emphasizes the existence of spatially disconnected rift systems. Based on their restoration, we suggest that the deformation was partitioned between a set of distinct left-lateral transtensional rift systems from the Late Jurassic to Early Cretaceous. A plate kinematic reorganization at Aptian-Albian time resulted in the onset of sea-floor spreading in the western Bay of Biscay and extreme crustal and lithosphere thinning in intra-continental rift basins to the east. The formation and reactivation of the IEPB is interpreted as the result of the polyphase evolution of a diffuse transient plate boundary that failed to localize. The results of this work may provide new insights on (1) processes preceding breakup and the initiation of segmented and strongly oblique shear margins, (2) the deformation history of nascent divergent plate boundaries, and (3) the kinematics of the southern North Atlantic and Alpine domain in western Europe.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Continental crust beneath Iceland [Earth, Atmospheric, and Planetary Sciences] (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-04-15
    Description: The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    The palaeo-bathymetry of base Aptian salt deposition on the northern Angolan rifted margin: constraints from flexural back-stripping and reverse post-break-up thermal subsidence modelling (2016)
    Geological Society of London
    Details
    Publication Date: 2016-01-28
    Description: The bathymetric datum with respect to global sea level for Aptian salt deposition in the South Atlantic is hotly debated. Some models propose that the salt was deposited in an isolated ocean basin in which local sea level was between 2 and 3 km below the global level. In this study, we use reverse post-break-up subsidence modelling to determine the palaeo-bathymetry of base Aptian salt deposition on the Angolan rifted continental margin. The reverse post-break-up subsidence modelling consists of the sequential flexural isostatic back-stripping of the post-break-up sedimentary sequences, decompaction of remaining sedimentary units and reverse modelling of post-break-up lithosphere thermal subsidence. The reverse modelling of post-break-up lithosphere thermal subsidence is carried out in 2D and requires knowledge of the continental lithosphere stretching factor (β), which is determined from gravity anomaly inversion. The analysis has been applied to the ION-GXT CS1-2400 deep long-offset seismic reflection profile, and two seismic cross-sections (P3 and P7+11) from offshore northern Angola. Reverse post-break-up subsidence modelling restores the proximal autochthonous base salt to between 0.2 and 0.6 km below global sea level at the time of break-up. In contrast, the predicted water-loaded bathymetries of the more distal base salt restored to break-up time are much greater between 2 and 3 km. The predicted bathymetries of the first unequivocal oceanic crust at break-up are approximately 2.5 km, as expected for newly formed oceanic crust of ‘normal’ thickness. Several interpretations of these results are possible. Our preferred interpretation is that all Aptian salt on the northern Angola rifted continental margin was deposited between 0.2 and 0.6 km beneath global sea level, and that the proximal salt subsided by post-rift (post-tectonic) thermal subsidence alone; while the distal salt formed during late syn-rift, when the underlying crust was actively thinning, resulting in additional tectonic subsidence (followed by post-rift thermal subsidence). An alternative interpretation is that the distal salt is para-autochthonous and moved downslope into much deeper water during and just after break-up. We do not believe that a deep isolated ocean basin, with a local sea level 2–3 km beneath that of the global sea level, as has been proposed, is required to explain the Aptian salt deposition on the northern Angolan rifted continental margin.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Geological Society of London
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