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  • 1
    Electronic Resource
    Electronic Resource
    Estimation of the Intrinsic Absorption and Scattering Attenuation in Northeastern Venezuela (Southeastern Caribbean) Using Coda Waves (1998)
    Springer
    Pure and applied geophysics 153 (1998), S. 685-702 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Coda waves, coda-Q−1, attenuation, scattering, Venezuela, Caribbean.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Northeastern Venezuela has been studied in terms of coda wave attenuation using seismograms from local earthquakes recorded by a temporary short-period seismic network. The studied area has been separated into two subregions in order to investigate lateral variations in the attenuation parameters. Coda-Q −1 (Q c −1) has been obtained using the single-scattering theory. The contribution of the intrinsic absorption (Q i −1) and scattering (Q s −1) to total attenuation (Q t −1) has been estimated by means of a multiple lapse time window method, based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Results show significant spatial variations of attenuation the estimates for intermediate depth events and for shallow events present major differences. This fact may be related to different tectonic characteristics that may be due to the presence of the Lesser Antilles subduction zone, because the intermediate depth seismic zone may be coincident with the southern continuation of the subducting slab under the arc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050214
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  • 2
    Electronic Resource
    Electronic Resource
    Imaging of shear-wave velocity structure beneath Iberia (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 124 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A detailed dispersion analysis of Rayleigh waves propagating across the Iberian Peninsula is carried out. The starting data are high-quality long-period data recorded at the broad-band NARS stations installed in (he Iberian Peninsula during the ILIHA project. We apply methods to obtain a correct selection of data and subsequent two-station surface-wave velocity measurements. A total of 64 teleseismic events recorded by the NARS array and 143 seismic paths have been studied. Several techniques which provide a significant improvement in the signal-to-noise ratio are employed to remove higher-mode interference efficiently and improve the isolation of the fundamental-mode Rayleigh wave from the seismograms. Thereafter, the interstation Rayleigh wave phase and group velocities are determined. We perform simultaneous inversion of phase-and group-velocity dispersion data by means of the stochastic inverse operator, and lest the reliability of the results by computing resolving kernels and also by forward modelling. A regionalization procedure based on the Backus-Gilbert approach for linear inversion of traveltime data is applied.Both the inversion results and the contoured shear-wave velocity panoramas display the main features of the deep structure of Iberia. We find a subcrustal low-velocity channel which extends over practically the whole peninsular area and spans a depth interval of approximately 40–50 km; it exhibits velocities of between 4.30 and 4.50 km s-1. At depths of 66–81 km, we find the highest velocities in the lithosphere, which reach values of 4.85 km s-1 in many cases. The low-velocity channel of the asthenosphere spans a large depth interval of approximately 80-180 km; it shows the lowest velocity values computed by us. We find velocities decreasing with depth, which are of the order of 4.25–4.36 km s-1 for the first 40 km and of the order of 4.00–4.25 km s-1 for the rest. The upper mantle under the asthenosphere exhibits high velocities, which range between 4.62 and 4.82 km s-1 in most cases.The shear-wave velocity structure of the Iberian subcrustal lithosphere and asthenosphere is mapped at 11 depth intervals from 24 to 201 km. At the top of the mantle, relatively low velocities span the Ebro Valley and also the southern third of the peninsula. Low velocities appear in the south-southwest quadrant, and high velocities occur over the Hercynian basement. At greater lithospheric depths, very low velocities extending over the whole peninsula suggest a low-velocity channel of non-uniform lateral structure, where a reduced zone to the west of the Iberian plateau shows relatively high velocities. At the greatest lithospheric depths, the whole Iberian block is fairly homogeneous laterally. The asthenosphere shows a notable lateral heterogeneity as well. We distinguish two parts: the upper asthenosphere, a 40 km thick layer with predominant velocity values of 4.25 km s or more; and the lower asthenosphere, a 60 km thick layer with velocity values generally below 4.25 km s-1. The upper asthenosphere seems to be less laterally heterogeneous than the lower asthenosphere. The lower asthenosphere exhibits a more pronounced negative velocity gradient than the upper asthenosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb07039.x
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  • 3
    Electronic Resource
    Electronic Resource
    Stress singularities in 2D orthotropic corners (1997)
    Springer
    International journal of fracture 83 (1997), S. 67-90 
    Details
    ISSN: 1573-2673
    Keywords: linear elasticity ; orthotropic materials ; stress singularities ; notches ; cracks ; Stroh relations ; composite materials.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new technique for analysis of two-dimensional linear elastostatic solutions with stress singularities at orthotropic corners is developed. An explicit and general representation of the associated eigenequation given as ‘zero determinant condition’ of a matrix with half dimension in comparison with the current approach is derived by application of Stroh relations of anisotropic elasticity. The technique is directly applicable to anisotropic corners. Analytical formulae for stress singularity exponents, roots of the associated eigenequations, at orthotropic half-plane and semiinfinite crack problems for all combinations of basic homogeneous boundary conditions, including slip with friction, are derived. it is noteworthy that the singularity exponents are invariant with respect to the relative orientation of boundary edges and orthotropic material for nine of these combinations. Numerical analysis of singularity exponents for some configurations typical in the modelization of material tests of fiber-matrix composite materials is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007336210450
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  • 4
    Electronic Resource
    Electronic Resource
    ON THE REMOVAL OF RIGID BODY MOTIONS IN THE SOLUTION OF ELASTOSTATIC PROBLEMS BY DIRECT BEM (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 4021-4038 
    Details
    ISSN: 0029-5981
    Keywords: boundary element method ; rigid-body motions ; support conditions ; elasticity ; Fredholm theory ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A theoretical and numerical study of the removal of rigid body motions in the solution of the boundary form of Somigliana identity and of the corresponding discretized linear system of the direct BEM is presented. This study is based on the Fredholm theory of linear operators and mechanical aspects of the problem. Various methods suitable for implementation in BEM codes are analyzed and relations between apparently different methods are shown. The relation between global equilibrium conditions and solvability of the discretized linear system of the direct BEM is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Photoelastic determination ofK I andK II : A numerical study on experimental data (1997)
    Springer
    Experimental mechanics 37 (1997), S. 45-55 
    Details
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The most efficient photoelastic methods to obtain stress intensity factors are those based on stress functions series expansions. The coefficients of these expansions are fitted to the experimental isochromatic pattern using an overdeterministic Newton-Raphson least squares method. In this paper, a study has been carried out to analyze the influence on the results of several numerical and experimental factors. It is shown that accurate values of the stress intensity factorsK I andK II can be obtained by following some recommendations given in the text and summarized in the conclusions at the end of the paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02328749
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  • 6
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    Improvements in the knowledge of the anelastic structure of the Iberian Peninsula from seismic data of the ILIHA project (1997)
    Oxford University Press
    Details
    Publication Date: 1997-06-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 7
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    Objective regionalization of Rayleigh-wave dispersion data by clustering algorithms (1997)
    Oxford University Press
    Details
    Publication Date: 1997-05-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 8
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    Photoelastic determination ofK I andK II : A numerical study on experimental data (1997)
    Springer
    Details
    Publication Date: 1997-03-01
    Print ISSN: 0014-4851
    Electronic ISSN: 1741-2765
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 9
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    Imaging of shear-wave velocity structure beneath Iberia (1996)
    Oxford University Press
    Details
    Publication Date: 1996-02-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 10
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    Hotspot volcanism close to a passive continental margin: the Canary Islands (1998)
    Cambridge University Press
    Details
    Publication Date: 1998-09-01
    Description: The Canarian Archipelago is a group of volcanic islands on a slow-moving oceanic plate, close to a continental margin. The origins of the archipelago are controversial: a hotspot or mantle plume, a zone of lithospheric deformation, a region of compressional block-faulting or a rupture propagating westwards from the active Atlas Mountains fold belt have been proposed by different authors. However, comparison of the Canarian Archipelago with the prototypical hotspot-related island group, the Hawaiian Archipelago, reveals that the differences between the two are not as great as had previously been supposed on the basis of older data. Quaternary igneous activity in the Canaries is concentrated at the western end of the archipelago, close to the present-day location of the inferred hotspot. This is the same relationship as seen in the Hawaiian and Cape Verde islands. The latter archipelago, associated with a well-defined but slow-moving mantle plume, shows anomalies in a plot of island age against distance which are comparable to those seen in the Canary Islands: these anomalies cannot therefore be used to argue against a hotspot origin for the Canaries. Individual islands in both archipelagoes are characterized by initial rapid growth (the ‘shield-building’ stages of activity), followed by a period of quiescence and deep erosion (erosion gap) which in turn is followed by a ‘post-erosional’ stage of activity. The absence of post-shield stage subsidence in the Canaries is in marked contrast with the major subsidence experienced by the Hawaiian Islands, but is comparable with the lack of subsidence evident in other island groups at slow-moving hotspots, such as the Cape Verdes. Comparison of the structure and structural evolution of the Canary Islands with other oceanic islands such as Hawaii and Réunion reveals many similarities. These include the development of triple (‘Mercedes Star’) rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones. The apparent absence of these features in the post-erosional islands may in part be a result of their greater age and deeper erosion, which has removed much of the evidence for their early volcanic architecture. We conclude that the many similarities between the Canary Islands and island groups whose hotspot origins are undisputed show that the Canaries have been produced in the same way.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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