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  • 1
    Call number: M 05.0602
    Type of Medium: Monograph available for loan
    Pages: 370 S. : zahlr. graph. Darst.
    ISBN: 3764362103
    Series Statement: Pageoph Topical Volumes
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 2
    Keywords: DEKORP ; seismic interpretation ; seismic signal srocessing ; seismic structure
    Description / Table of Contents: DEKORP, the German continental reflection seismic program, was the major focus of deep seismic research in Germany in the 1980s and 1990s. The seismic sections provided fundamental new insight into deep geological structure of the European continent and the dynamics of continental formation. They formed the basis for worldwide comparative studies of orogenic structure. The complicated signature of the reflections from the deep crust indicated that new processing and interpretation techniques must be considered to better image the crystalline crust. Results of these efforts, including pre-stack migration, 3-D imaging, shear waves and seismic anisotropy, are presented in this special volume. In part, the articles open the perspective to new and future research. In part, they document research activity triggered by technical and interpretational questions raised by DEKORP field work and profiling results. Many of the presented methods can find immediate application in industrial seismic prospecting.
    Pages: Online-Ressource (VI, 370 Seiten)
    ISBN: 9783764362102
    Language: English
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  • 3
    Call number: 21/STR 07/03
    In: Scientific technical report
    Type of Medium: GFZ publications
    Pages: 228 S.
    Series Statement: Scientific technical report / GeoForschungsZentrum Potsdam STR 07/03
    Location: Reading room
    Branch Library: GFZ Library
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  • 4
    Call number: 9/M 09.0155
    Description / Table of Contents: Sedimentary basins host, among others, most of our energy and fresh-water resources: they can be regarded as large geo-reactors in which many physical and chemical processes interact. Their complexity can only be well understood in well-organized interdisciplinary co-operations.This book documents how researchers from different geo-scientific disciplines have jointly analysed the structural, thermal, and sedimentary evolution as well as fluid dynamics of a complex sedimentary basin system which has experienced a variety of activation and reactivation impulses as well as intense salt tectonics. In this book we have summarized our geological, geophysical and geochemical understanding of some of the most important processes affecting sedimentary basins in general and our view on the evolution of one of the largest, best explored and most complex continental sedimentary basins on Earth: The Central European Basin System. - Characteristics of complex intracontinental sedimentary basins.- The Central European Basin System.- Strain and temperature in space and time.- Basin fill.- Salt dynamics.- Fluid systems.
    Type of Medium: Monograph available for loan
    Pages: XXIV, 520 S. + 1 CD-ROM , 49 schw.-w. Ill., 334 farb. Ill., 24 schw.-w. Tab., 1 schw.-w. Fotos, 23 farb. Fotos, 48 schw.-w. graph. Darst., 311 farb. graph. Darst.
    ISBN: 9783540850847
    Classification: A.3.16.
    Location: Reading room
    Branch Library: GFZ Library
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  • 5
    ISSN: 1420-9136
    Keywords: Borehole modeling ; finite-difference method ; grid refinement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A finite-difference approach of aP-SV modeling scheme is applied to compute seismic wave propagation in heterogeneous isotropic media, including fluid-filled boreholes. The discrete formulation of the equation of motion requires the definition of the material parameters at the grid points of the numerical mesh. The grid spacing is chosen as coarse as possible with respect to the accurate representation of the shortest wavelength. If we assume frequencies lower than 250 Hz then the grid spacing is usually chosen in the range of a few meters. One encounters difficulties because of the large-scale difference between the grid spacing and the size of the borehole, usually several centimeters. These difficulties can be overcome by a grid refinement technique. This technique provides the construction of grids with varying grid spacing. The grid spacing in the vicinity of the borehole is chosen such that the borehole is properly represented. An example demonstrates the accuracy of this technique by comparisons with other methods. Unlike many analytical methods, the FD method can handle complex subsurface geometries. Further numerical examples of walk-awayVSP configurations show tube wave propagation within fluid-filled boreholes of realistic diameters.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    PO Box 1354, 9600 Garsington Road , Oxford OX4 2XG , UK . : Blackwell Science Ltd
    Geophysical prospecting 53 (2005), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: For multivalued traveltime computation on dense grids, we propose a wavefront-orientated ray-tracing (WRT) technique. At the source, we start with a few rays which are propagated stepwise through a smooth two-dimensional (2D) velocity model. The ray field is examined at wavefronts and a new ray might be inserted between two adjacent rays if one of the following criteria is satisfied: (1) the distance between the two rays is larger than a predefined threshold; (2) the difference in wavefront curvature between the rays is larger than a predefined threshold; (3) the adjacent rays intersect. The last two criteria may lead to oversampling by rays in caustic regions. To avoid this oversampling, we do not insert a ray if the distance between adjacent rays is smaller than a predefined threshold. We insert the new ray by tracing it from the source. This approach leads to an improved accuracy compared with the insertion of a new ray by interpolation, which is the method usually applied in wavefront construction. The traveltimes computed along the rays are used for the estimation of traveltimes on a rectangular grid. This estimation is carried out within a region bounded by adjacent wavefronts and rays. As for the insertion criterion, we consider the wavefront curvature and extrapolate the traveltimes, up to the second order, from the intersection points between rays and wavefronts to a gridpoint. The extrapolated values are weighted with respect to the distances to wavefronts and rays. Because dynamic ray tracing is not applied, we approximate the wavefront curvature at a given point using the slowness vector at this point and an adjacent point on the same wavefront. The efficiency of the WRT technique is strongly dependent on the input parameters which control the wavefront and ray densities. On the basis of traveltimes computed in a smoothed Marmousi model, we analyse these dependences and suggest some rules for a correct choice of input parameters. With suitable input parameters, the WRT technique allows an accurate traveltime computation using a small number of rays and wavefronts.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Geophysical prospecting 50 (2002), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: To carry out a 3D prestack migration of the Kirchhoff type is still a task of enormous computational effort. Its efficiency can be significantly enhanced by employing a fast traveltime interpolation algorithm. High accuracy can be achieved if second-order spatial derivatives of traveltimes are included in order to account for the curvature of the wavefront. We suggest a hyperbolic traveltime interpolation scheme that permits the determination of the hyperbolic coefficients directly from traveltimes sampled on a coarse grid, thus reducing the requirements in data storage. This approach is closely related to the paraxial ray approximation and corresponds to an extension of the well-known 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR0285:GPR_0285_mu1" location="equation/GPR_0285_mu1.gif"/〉 method to arbitrary heterogeneous and complex media in 3D. Application to various velocity models, including a 3D version of the Marmousi model, confirms the superiority of our method over the popular trilinear interpolation. This is especially true for regions with strong curvature of the local wavefront. In contrast to trilinear interpolation, our method also provides the possibility of interpolating source positions, and it is 5–6 times faster than the calculation of traveltime tables using a fast finite-difference eikonal solver.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Conventional finite-difference modelling algorithms for seismic forward modelling are based on a time-stepping scheme with a constant (global) time step. Large contrasts in the velocity model or in the spatial sampling rate cause oversampling in time for some regions of the model. The use of locally adjustable time steps can save large amounts of computation time for certain modelling configurations.  The computation of spatial derivatives across the transition zone between regions of the model with different temporal sampling requires the definition of the wavefield at corresponding time levels on both sides of the transition zone. This condition can be obtained by extrapolation in time, which is inaccurate, or by multiple time integration in the transition zone. The error in the latter solution is of the same order as the conventional time-stepping scheme because both methods are based on the same iteration formula. The technique of multiple time integration simply requires the use of different sizes of time step. It is applicable only for certain factors of variation of the time step.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A procedure to evaluate the geometrical properties of the slowness surface for arbitrary anisotropic media is presented. This allows us to use results for computing the displacement field from point sources in general anisotropic media utilizing the Gaussian curvature of the slowness surface of the considered waves. Since the formulae used are based on high frequency asymptotics the procedure gives reliable results as long as no parabolic points of the slowness surface are encountered. Radiation patterns of point sources for models representing rocks in the crust and upper mantle are presented and discussed. The radiation from point sources in anisotropic models is compared with the radiation from point sources in average isotropic models to emphasize the differences. Anisotropy is either caused by aligned cracks (crustal rocks) or by aligned olivine crystals (upper mantle rocks). Considering models of aligned cracks differing only in the physical parameters of the crack material (water or gas) significantly different radiation patterns are obtained. Models with wet cracks exhibit focusing of quasi S-wave energy for some directions whereas this effect is not observed for the corresponding model with dry cracks. The quasi S-wave radiation pattern from explosions are multilobed and the wet crack models exhibit more lobes than the dry crack models. The radiation of single forces in olivine shows strong energy focusing (wave tuning) of quasi S waves, however, for realistic compositions of upper mantle rocks with some 10 per cent of preferentially orientated olivine this wave tuning is less pronounced.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2018-07-04
    Description: Multichannel seismic (MCS) data from the Yaquina forearc basin off Peru reveal a complex distribution of gas and gas hydrate related reflections. Lateral variations of the reflection pattern at the assumed base of the gas hydrate stability zone in terms of continuity, amplitude, and signal attenuation underneath are observed, as well as the possible occurrence of paleo-bottom simulating reflectors (BSRs). Phase reversed reflections above the bottom simulating reflector point to free gas within the gas hydrate stability zone (GHSZ). To constrain the interpretation of the observed reflection pattern we calculated the velocity distribution along the MCS line from high-resolution ocean bottom hydrophone recordings with two independent methods. Heat flux values estimated on the basis of the velocity-depth functions increase with decreasing amplitude of the BSR and peak near chemoherms. These results suggest a model of the Yaquina Basin where free gas is trapped under parts of the BSR, and within the GHSZ, particularly under the seafloor and under an erosional unconformity. The hypothesis of a paleo-BSR that reflects the uplift of the base of the hydrate stability zone caused by the deposition of a particular sediment sequence is supported by the estimated heat flux values.
    Type: Article , PeerReviewed
    Format: text
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