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  • 1
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    3D True-amplitude finite-offset migration (1992)
    Geophys. Institut der Universität Karlsruhe
    In:  subm. to Geophysics, Hannover, Geophys. Institut der Universität Karlsruhe, vol. 5, no. 1, pp. 164-173, pp. 1175, (ISSN: 1340-4202)
    Details
    Publication Date: 1992
    Keywords: Scattering ; Inversion ; Generalized Radon Transformation ; seismic Migration ; Three dimensional ; Seismics (controlled source seismology)
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    True-amplitude migration (1990)
    Deutsche Geophys. Ges.
    In:  DGG-Seminar, Neustadt/Weinstraße, Deutsche Geophys. Ges., vol. 1034, no. 1, pp. 1075, (ISBN 3-933346-037)
    Details
    Publication Date: 1990
    Keywords: Seismics (controlled source seismology) ; seismic Migration
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Estimating fracture orientation from elastic-wave propagation: An ultrasonic experimental approach (2012)
    Wiley
    Details
    Publication Date: 2012-08-18
    Description: Elastic-wave propagation in fractured and cracked media depends on the dominant spatial orientation of the discontinuities. Consequently, compressional and shear-wave velocities can give valuable information about the orientation of the cracks. The main goal of this work is to estimate the preferential fracture orientation based on an analysis of cross-correlated S-wave seismograms and Thomsen parameters. For this purpose, we analyzed ultrasonic measurements of elastic (P and S) waves in a physical-modeling experiment with an artificially anisotropic cracked model. The solid matrix of the model consisted of epoxy-resin; small rubber strips simulate cracks with a compliant fill. The anisotropic cracked model consists of three regions, each with a different fracture orientation. We used the rotation of the S-wave polarizations for a cross-correlation analysis of the orientations, and P- and S-wave measurements to evaluate the weak anisotropic parameters γ and ε. The shear and compressional wave sources had dominant frequencies of 90 kHz and 120 kHz. These frequencies correspond to long wavelengths compared to the spacing between layers, indicating a nearly effective-media behavior. Integrating the results from cross-correlation with anisotropic parameter analysis, we were able to estimate the fracture orientation in our anisotropic cracked physical model. The γ parameter showed good agreement with the cross-correlation analysis and, beyond that, provided additional information about the crack orientation that cross-correlation alone did not fully resolve. Moreover, our results show that the shear waves are much more strongly influenced by, and can thus contain more information about, crack orientation than compressional waves.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    X-ray emission from star-forming galaxies - signatures of cosmic rays and magnetic fields (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-12
    Description: The evolution of magnetic fields in galaxies is still an open problem in astrophysics. In nearby galaxies the far-infrared–radio correlation indicates the coupling between magnetic fields and star formation. The correlation arises from the synchrotron emission of cosmic ray electrons travelling through the interstellar magnetic fields. However, with an increase of the interstellar radiation field (ISRF), inverse Compton scattering becomes the dominant energy loss mechanism of cosmic ray electrons with a typical emission frequency in the X-ray regime. The ISRF depends on the one hand on the star formation rate and becomes stronger in starburst galaxies, and on the other hand increases with redshift due to the higher temperature of the cosmic microwave background. With a model for the star formation rate of galaxies, the ISRF, and the cosmic ray spectrum, we can calculate the expected X-ray luminosity resulting from the inverse Compton emission. Except for galaxies with an active galactic nucleus the main additional contribution to the X-ray luminosity comes from X-ray binaries. We estimate this contribution with an analytical model as well as with an observational relation, and compare it to the pure inverse Compton luminosity. Using data from the Chandra Deep Field Survey and far-infrared observations from Atacama Large Millimeter/Submillimeter Array, we then determine upper limits for the cosmic ray energy. Assuming that the magnetic energy in a galaxy is in equipartition with the energy density of the cosmic rays, we obtain upper limits for the magnetic field strength. Our results suggest that the mean magnetic energy of young galaxies is similar to the one in local galaxies. This points towards an early generation of galactic magnetic fields, which is in agreement with current dynamo evolution models.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Hollywood, climate change, and the public (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-09-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Balmford, Andrew -- Manica, Andrea -- Airey, Lesley -- Birkin, Linda -- Oliver, Amy -- Schleicher, Judith -- New York, N.Y. -- Science. 2004 Sep 17;305(5691):1713.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15375246" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Mineral characterization, clay quantification and Ar-Ar dating of faulted schists in the Carboneras and Palomares Faults (Betic Cordillera, SE Spain) (2017)
    Schweizerbart
    Details
    Publication Date: 2017-03-08
    Description: Two major clay-rich fault zones (Betic Cordillera, SE Spain) exhumed under arid conditions were studied to establish the origin and nature of phyllosilicates in deformed mica schists and the role of fault zones in the genesis of rocks rich in clay minerals. Both areas contain wide zones (200 m across) of alternating fault gouge and protolith creating a complex arrangement of sheared lenses along fault strand cores. Minerals in schists were characterized by X-ray diffractometry and scanning and transmission electron microscopy, and two samples were selected for 40 Ar/ 39 Ar dating of four clay grain-size fractions each. Quartz, chlorite and K-micas are the principal phases in all samples (crystalline protolith and faulted schists). Paragonite and Fe and Ti-oxides are present in some samples and, additionally, most of the damaged samples have kaolinite, illite and gypsum. Backscattered electron images show irregularly oriented stacks of phyllosilicates with curved shapes in the fault rocks and quartz grains deformed by brittle fracturing. Clay fabrics in the damaged rocks are poorly developed. Lattice fringe images of faulted damaged samples revealed defect-free dioctahedral mica and Fe-rich chlorite packets which were generally with no more than several tens of nm thickness, although chlorite grains were usually thicker than micas. Chlorite showed more obvious deformation features. The calculated ages of the authigenic clay component in the two samples are 6.3 ± 0.8 Ma and 6.2 ± 0.4 Ma, while the ages calculated for the protolith clays are 22.8 ± 1.9 Ma and 11.7 ± 1.3 Ma. The age of the authigenic clay overlaps the range of ages from the nearby Cabo de Gata volcanic series (SE Spain). Textural and chemical results point toward that although the fault gouge is mostly a product of mechanical crushing of the protolith, the presence of quartz provided a strong and fragile behaviour to the faulted rocks increasing their permeability, and creating permeable paths through which low-temperature hydrothermal fluids circulated producing an intense leaching of the parent material and promoting crystallization of new authigenic minerals (illite, kaolinite, smectite and gypsum).
    Print ISSN: 0935-1221
    Electronic ISSN: 1617-4011
    Topics: Geosciences
    Published by Schweizerbart
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  • 7
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    Three-Dimensional Complex Padé FD Migration: Splitting and Corrections (2013)
    Hindawi
    Details
    Publication Date: 2013-01-22
    Description: Three-dimensional wave-equation migration techniques are still quite expensive because of the huge matrices that need to be inverted. Several techniques have been proposed to reduce this cost by splitting the full 3D problem into a sequence of 2D problems. To reduce errors, the Li correction is applied at regular multiples of depth extrapolation increment. We compare the performance of splitting techniques in wave propagation for 3D finite-difference (FD) migration in terms of image quality and computational cost. We study the behaviour of the complex Padé approximation in combination with two- and alternating four-way splitting, that is, splitting into the coordinate directions at one depth and the diagonal directions at the next depth level. We also extend the Li correction for use with the complex Padé expansion and diagonal directions. From numerical examples in inhomogeneous media, we conclude that alternate four-way splitting is the most cost-effective strategy to reduce numerical anisotropy in complex Padé 3D FD migration.
    Print ISSN: 1687-885X
    Electronic ISSN: 1687-8868
    Topics: Geosciences
    Published by Hindawi
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  • 8
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    Automatic detection and imaging of diffraction points using pattern recognition (2012)
    Wiley
    Details
    Publication Date: 2012-12-08
    Description: ABSTRACT Hydrocarbon reservoirs are generally located beneath complex geological structures. Frequently, such areas contain seismic diffractors that carry detailed structure information in the order of the seismic wavelength. Therefore, the development of computational facilities capable of detecting diffractor points with a good resolution is desirable but has been a challenge in the area of seismic processing. In this work, we present a method for the detection of diffraction points in the common-offset-gather domain. The method applies a two-class k nearest neighbours (kNN) pattern recognition technique to amplitudes along diffraction traveltime curves to distinguish between diffractions and reflections or noise. While the method, in principle, requires knowledge of the migration velocity field, it is very robust with respect to an erroneous model. Numerical examples using synthetic seismic and field ground-penetrating-radar (GPR) data demonstrate the feasibility of the technique and show its usefulness for automatically mapping diffraction points in a seismic section. In our applications, the method was able to detect all diffractions present in the data and did not produce any false positives.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
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  • 9
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    Three-Dimensional Complex Padé FD Migration: Splitting and Corrections (2013)
    Hindawi
    Details
    Publication Date: 2013-01-02
    Description: Three-dimensional wave-equation migration techniques are still quite expensive because of the huge matrices that need to be inverted. Several techniques have been proposed to reduce this cost by splitting the full 3D problem into a sequence of 2D problems. To reduce errors, the Li correction is applied at regular multiples of depth extrapolation increment. We compare the performance of splitting techniques in wave propagation for 3D finite-difference (FD) migration in terms of image quality and computational cost. We study the behaviour of the complex Padé approximation in combination with two- and alternating four-way splitting, that is, splitting into the coordinate directions at one depth and the diagonal directions at the next depth level. We also extend the Li correction for use with the complex Padé expansion and diagonal directions. From numerical examples in inhomogeneous media, we conclude that alternate four-way splitting is the most cost-effective strategy to reduce numerical anisotropy in complex Padé 3D FD migration.
    Print ISSN: 1687-885X
    Electronic ISSN: 1687-8868
    Topics: Geosciences
    Published by Hindawi
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  • 10
    Electronic Resource
    Electronic Resource
    True-amplitude migration of 2D synthetic data (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: True-amplitude (TA) migration, which is a Kirchhoff-type modified weighted diffraction stack, recovers (possibly) complex angle-dependent reflection coefficients which are important for amplitude-versus-offset (AVO) inversion. The method can be implemented using existing prestack or post-stack Kirchhoff migration and fast Green's function computation programs. Here, it is applied to synthetic single-shot and constant-offset seismic data that include post-critical reflections (complex reflection coefficients) and caustics. Comparisons of the amplitudes of the TA migration image with theoretical reflection coefficients show that the (possibly complex) angle-dependent reflection coefficients are correctly estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1994.tb00220.x
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    Paper (German National Licenses)
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