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  • 1
    Monograph available for loan
    Monograph available for loan
    Seismic interferometry (2010)
    Cambridge : Cambridge Univ. Press
    Details Availability
    Call number: M 11.0002
    Description / Table of Contents: Contents: Preface; 1. Introduction; 2. Reciprocity equations of convolution and correlation types; 3. VSP SWP correlation transform; 4. VSP SSP correlation transform; 5. VSP SSP convolution transform; 6. SSP SSP correlation transform; 7. VSP VSP correlation transform; 8. SSP VSP SWP transforms; 9. Traveltime interferometry; 10. Stochastic interferometry; 11. Interferometric source estimation; 12. Body wave earthquake interferometry; References; Index
    Type of Medium: Monograph available for loan
    Pages: XI, 260 S.
    ISBN: 9780521169332 , 0-521-16933-X
    Classification:
    Seismology
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    Wave equation inversion of skeletalized geophysical data (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 105 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Inversion methods based on gradient optimization techniques require the directional derivative of the data with respect to the model parameters. Unfortunately, the data (e.g., pressure seismograms) are usually restricted to that explicitly given in the fundamental governing equation (e.g., wave equation). This limited choice of data type may lead to misfit functions that are pathologically non-linear with respect to the model parameters. We present a methodology which allows for the calculation of directional derivatives for skeletalized data sets, yet still uses the fundamental governing equations without the need for approximations. Skeletalized data are defined as a reduced data set derived from the original data which retains the important information about the model parameter of interest. The motivation for working with skeletalized data rather than raw data is that the skeleton data may be strongly influenced by only one type of model parameter and lead to a quasi-linear misfit function.Examples of skeletalized data sets include first arrival traveltimes picked from CDP seismograms for velocity inversion, amplitudes of transmitted earthquake SH-waves for earthquake moment inversion, or pulse width measured from first arrivals for attenuation inversion. As an example we devise a traveltime inversion method based on the wave equation and free of any high-frquency approximations. Results show that wave equation traveltime (WT) inversion is superior to ray traced traveltime inversion for complicated velocity models. It is also shown that WT inversion converges quickly for starting velocity models that are far from the actual model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb06713.x
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  • 3
    Electronic Resource
    Electronic Resource
    Causes of low-frequency ground motion amplification in the Salt Lake Basin: the case of the vertically incident P wave (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 122 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We use simulations of 1-D, 2-D and 3-D wave propagation to identify the major causes of low-frequency (0.2–1.2 Hz) seismic amplification in the Salt Lake Basin. For a simple two-layer basin model and a vertically incident P wave, we examine how amplification is influenced by mode conversion, surface-wave generation, impedance effects at the sediment-bedrock boundary, resonance, and 2-D and 3-D focusing and scattering. Results show the following.(1) Approximately 30 per cent of the total cumulative kinetic energy at the Salt Lake Valley floor consists of shear-wave energy generated by P-to-S converted waves and surface waves. The surface waves appear to be generated primarily along the edges of the basin, and the instantaneous S/P energy ratio in the sedimentary layer is as large as 3.(2) The largest peak particle velocity at the free surface is due to the direct P wave. The value is roughly predicted by the transmission coefficient of 1.46 at the sediment-bedrock interface, i.e. a normally incident P wave in the stiff bedrock will be magnified in amplitude by 1.46 times as it enters the softer sediments.(3) The low-frequency elastic response of the two-layer Salt Lake Basin model is characterized by surface-wave propagation and resonance from vertically interfering waves.(4) The peak particle velocities, cumulative kinetic energies, and mean spectral magnitudes computed from the 2-D (1-D) synthetics underestimate the values computed from the 3-D synthetics by up to 40 per cent (48 per cent) along a profile above the deepest part of the basin model. The 2-D and 1-D signal duration times underestimate the 3-D values by up to 59 and 94 per cent, respectively. Our results suggest that 2-D basin modelling may yield good approximations to the 3-D ground motion amplification above the deepest part of the Salt Lake Basin.Our results show that several mechanisms contribute significantly to low-frequency seismic amplification in the semi-consolidated sediments of the Salt Lake Basin—P-to-S wave conversion, surface-wave generation, impedance effects at the sediment-bedrock boundary, and resonance. Future attempts to estimate ground motion amplification in the Salt Lake Basin should therefore account for the amplification effects of all these mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb06854.x
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  • 4
    Electronic Resource
    Electronic Resource
    3D wavepath migration (2003)
    PO Box 1354, 9600 Garsington Road , Oxford OX4 2XG , UK . : Blackwell Publishing Ltd
    Geophysical prospecting 51 (2003), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: 3D Kirchhoff migration (KM) smears a trace's time sample along a quasi-ellipsoid in the model space. This is a costly and sometimes noisy process as reflection energy is smeared far away from the actual reflector position, introducing far-field migration artefacts. As a reduced form of 3D KM, 3D wavepath migration (WM) smears a picked reflection arrival to a small Fresnel zone portion centred about the specular reflection point, leading to fewer migration artefacts and reduced computation time. Both the traveltime and the angle of incidence are required by WM for locating the specular reflection point. Our results with 3D prestack synthetic data show that WM generates fewer migration artefacts and can sometimes define complex structure better than KM. Our results with 3D prestack field data show that WM can mostly suppress migration artefacts and can sometimes resolve reflection interfaces better than KM. The CPU comparison shows that, for both the synthetic and field data examples, WM can be more than an order of magnitude faster than KM. The limitation with 3D WM is that the angle of incidence calculation is sensitive to the recording geometry and the signal-to-noise (S/N) ratio, which can lead to blurred images.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.2003.00380.x
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  • 5
    Electronic Resource
    Electronic Resource
    Resolution limits for crosswell migration and traveltime tomography (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 127 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Equations are derived for the point-scatterer response of the crosswell migration and traveltime tomography operators. These formulas are used to estimate the limits of spatial resolution in reflection migration images and traveltime tomograms. In particular, for a crosswell geometry with borehole length L, well offset 2x0, source wavelength δ, and a centred point scatterer I show the following.(1) The vertical resolution Δzmig of the reflection migration image is equal to 2δx0/L under the far-field approximation. Under the Fresnel approximation, Δzmig≈2δx0/L-2δ2/L, which says that images become better resolved with an increase in aperture and a decrease in wavelength and well offset.(2) The horizontal resolution Δzmig of the migration image is equal to 16δx02/L2. The lateral resolution of the migrated image is worse than the vertical resolution by a factor of 8x0/L (where x0/L〉 1 under the far-field approximation).(3) The vertical resolution Δztomo of the traveltime velocity tomogram is proportional to √λx0. This estimate agrees with that of a previous study. However, the tomographic image of the slowness perturbation behaves as a non-local cosine function along the depth axis, whereas the migration image behaves as a localized squared sine function in the depth coordinate. This is consistent with the empirical observation that interface boundaries are more sharply resolved by migration than by traveltime tomography.(4) The horizontal resolution of the slowness image in a traveltime tomogram is equal to (4x0/L}√3x0δ/4, a factor more than 4x0/L worse than the vertical resolution.(5) For Ns sources and Ng geophones, the dynamic range of the migrated image is proportional to NsNg. The dynamic range of the slowness tomogram is proportional to √NgNs.Many of the estimates for the resolution limits have simple geometrical interpretations. For example, the minimum vertical (horizontal) resolution in a migrated reflectivity section corresponds to the minimum vertical (horizontal) stretch that a migrated wavelet undergoes in going from the time domain to the depth domain. In addition, the minimum vertical (horizontal) resolution in a traveltime tomogram corresponds to the minimum vertical (horizontal) width of the wavepath at the scatterer location
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb04731.x
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  • 6
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    Enhanced refractor imaging by supervirtual interferometry (2011)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2011-05-01
    Description: Refraction surveys are a well-established method of imaging subsurface velocities, both in terms of the deep crustal structure at global scales and in the shallow near surface. These surveys generally involve deploying an array of receivers on the surface (or water bottom) and recording arrivals from a seismic source initiated at or near the surface.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
    Published by Society of Exploration Geophysicists (SEG)
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  • 7
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    Least-squares migration of multisource data with a deblurring filter (2011)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2011-09-01
    Description: Least-squares migration (LSM) has been shown to be able to produce high-quality migration images, but its computational cost is considered to be too high for practical imaging. We have developed a multisource least-squares migration algorithm (MLSM) to increase the computational efficiency by using the blended sources processing technique. To expedite convergence, a multisource deblurring filter is used as a preconditioner to reduce the data residual. This MLSM algorithm is applicable with Kirchhoff migration, wave-equation migration, or reverse time migration, and the gain in computational efficiency depends on the choice of migration method. Numerical results with Kirchhoff LSM on the 2D SEG/EAGE salt model show that an accurate image is obtained by migrating a supergather of 320 phase-encoded shots. When the encoding functions are the same for every iteration, the input/output cost of MLSM is reduced by 320 times. Empirical results show that the crosstalk noise introduced by blended sources is more effectively reduced when the encoding functions are changed at every iteration. The analysis of signal-to-noise ratio (S/N) suggests that not too many iterations are needed to enhance the S/N to an acceptable level. Therefore, when implemented with wave-equation migration or reverse time migration methods, the MLSM algorithm can be more efficient than the conventional migration method.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
    Published by Society of Exploration Geophysicists (SEG)
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  • 8
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    Multiparameter deblurring filter and its application to elastic migration and inversion (2018)
    Society of Exploration Geophysicists
    Details
    Publication Date: 2018-06-22
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
    Published by Society of Exploration Geophysicists
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  • 9
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    Opportunities and pitfalls in surface-wave interpretation (2017)
    Society of Exploration Geophysicists
    Details
    Publication Date: 2017-02-01
    Description: Many explorationists think of surface waves as the most damaging noise in land seismic data. Thus, much effort is spent in designing geophone arrays and filtering methods that attenuate these noisy events. It is now becoming apparent that surface waves can be a valuable ally in characterizing the near-surface geology. This review aims to find out how the interpreter can exploit some of the many opportunities available in surface waves recorded in land seismic data. For example, the dispersion curves associated with surface waves can be inverted to give the S-wave velocity tomogram, the common-offset gathers can reveal the presence of near-surface faults or velocity anomalies, and back-scattered surface waves can be migrated to detect the location of near-surface faults. However, the main limitation of surface waves is that they are typically sensitive to S-wave velocity variations no deeper than approximately half to one-third the dominant wavelength. For many exploration surveys, this limits the depth of investigation to be no deeper than approximately 0.5–1.0 km.
    Print ISSN: 2324-8858
    Electronic ISSN: 2324-8866
    Topics: Geosciences
    Published by Society of Exploration Geophysicists
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  • 10
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    Skeletonized wave-equation inversion in vertical symmetry axis media without too much math (2017)
    Society of Exploration Geophysicists
    Details
    Publication Date: 2017-08-31
    Description: We have developed a tutorial for skeletonized inversion of pseudo-acoustic anisotropic vertical symmetry axis (VTI) data. We first invert for the anisotropic models using wave-equation traveltime inversion. Here, the skeletonized data are the traveltimes of transmitted and/or reflected arrivals that lead to simpler misfit functions and more robust convergence compared with full-waveform inversion. This provides a good starting model for waveform inversion. The effectiveness of this procedure is illustrated with synthetic data examples and a marine data set recorded in the Gulf of Mexico.
    Print ISSN: 2324-8858
    Electronic ISSN: 2324-8866
    Topics: Geosciences
    Published by Society of Exploration Geophysicists
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