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  • 1
    Monograph available for loan
    Monograph available for loan
    Frankfurt, M. : Bundesamt für Kartographie und Geodäsie
    Associated volumes
    Call number: S 95.0116(37)
    In: IERS technical note
    Type of Medium: Monograph available for loan
    Pages: 54S. : graph. Darst.
    ISBN: 9783864820465
    Series Statement: IERS technical note 37
    Classification: A.1.3.
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Series available for loan
    Series available for loan
    Frankfurt am Main : Verlag des Bundesamts für Kartographie und Geodäsie
    Associated volumes
    Call number: S 95.0116(38)
    In: IERS technical note
    Type of Medium: Series available for loan
    Pages: 73 Seiten , Illustrationen
    ISBN: 9783864820885
    Series Statement: IERS Technical Note No. 38
    Language: German
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 3
    Publication Date: 2016-12-28
    Description: Full-waveform inversion starts being used as a standard stage of the seismic-imaging workflow, at the exploration scale, for the reconstruction of high-resolution wave velocity models. However, its successful application still relies on the estimation of an accurate enough initial velocity model, as well as on the design of a suitable hierarchical workflow, allowing it to feed the inversion process progressively with data. These two requirements are mandatory to avoid the cycle-skipping or phase-ambiguity problem when comparing observed and synthetic data. This difficulty is due to the definition of the full-waveform inversion problem as the least-squares minimization of the data misfit. The resulting misfit function has local minima, which correspond to the interpretation of the seismic data up to one or several phase shifts. In this article, we review an alternative formulation of full-waveform inversion based on the optimal transport distance we have proposed in recent studies. We propose to use a particular instance of the optimal transport problem, which is adapted to the interpretation of real seismic data and for which we design an efficient low-complexity numerical strategy. Numerical results in 2D and 3D configurations (BP 2004, Chevron 2014 benchmark model, SEG/EAGE overthrust model) show that this reformulation should yield a more convex misfit function, less prone to cycle skipping. In this study, we present a simple illustration on the Marmousi model, which illustrates how this new distance strongly relaxes the requirement on the initial model design. Starting from a rather simplistic approximation of the initial model, the method is able to reconstruct a meaningful estimation of the Marmousi model, while the standard least-squares formulation is trapped into a local, meaningless minimum.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
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  • 4
    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Land seismic multiparameter full waveform inversion in anisotropic media is challenging because of high medium contrasts and surface waves. With a data-residual least-squares objective function, the surface wave energy usually masks the body waves and the gradient of the objective function exhibits high values in the very shallow depths preventing from recovering the deeper part of the earth model parameters. The optimal transport objective function, coupled with a Gaussian time-windowing strategy, allows to overcome this issue by more focusing on phase shifts and by balancing the contributions of the different events in the adjoint-source and the gradients. We first illustrate the advantages of the optimal transport function with respect to the least-squares one, with two realistic examples. We then discuss a vertical transverse isotropic (VTI) example starting from a quasi 1-D isotropic initial model. Despite some cycle-skipping issues in the initial model, the inversion based on the windowed optimal transport approach converges. Both the near-surface complexities and the variations at depth are recovered.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 5
    Publication Date: 2015-04-16
    Description: A method for combining the asymptotic operator designed by Beylkin (Born migration operator) for the solution of linearized inverse problems with full waveform inversion is presented. This operator is used to modify the standard L 2 norm that measures the distance between synthetic and observed data. The modified misfit function measures the discrepancy of the synthetic and observed data after they have been migrated using the Beylkin operator. The gradient of this new misfit function is equal to the cross-correlation of the single scattering data with migrated/demigrated residuals. The modified misfit function possesses a Hessian operator that tends asymptotically towards the identity operator. The trade-offs between discrete parameters are thus reduced in this inversion scheme. Results on 2-D synthetic case studies demonstrate the fast convergence of this inversion method in a migration regime. From an accurate estimation of the initial velocity, three and five iterations only are required to generate high-resolution P -wave velocity estimation models on the Marmousi 2 and synthetic Valhall case studies.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
    Publication Date: 2016-02-20
    Description: Joint analysis of the seismic velocities and geoid, gravity and gravity gradients are used to constrain the viscosity profile within the mantle as well as the lateral density variations. Recent ESA's Gravity field and steady-state Ocean Circulation Explorer measurements of the second-order derivatives of the Earth's gravity potential give new possibilities to determine these mantle properties. Using a simple mantle model and seismic tomography results, we investigate how the gravitational potential, the three components of the gravity vector and the gravity gradients can bring information on the radial viscosity profile and on the mantle mass anomalies. We start with lateral density variations in the Earth's mantle based either on slab history or deduced from seismic tomography. The main uncertainties are: for the latter case, the relationship between seismic velocity and density—the so-called density/velocity scaling factor—and for the former case, the variation with depth of the density contrast between the cold slabs and the surrounding mantle. We perform a Monte Carlo search for the viscosity and the density/velocity scaling factor profiles within the mantle, which allows to fit the observed geoid, gravity and gradients of gravity. We compute the posterior probability distribution of the unknown parameters, and find that the gravity gradients improve the estimate of the scaling factor within the upper mantle, because of their sensitivity to the masses within the upper mantle, whereas the geoid and the gravity better constrain the scaling factor in the lower mantle. In the upper mantle, it is less than 0.02 in the upper part and about 0.08–0.14 in the lower part, and it is significantly larger for depths greater than 1200 km (about 0.32–0.34). In any case, the density/velocity scaling factor between 670 and 1150 km depth is not well constrained. We show that the viscosity of the upper part of the mantle is strongly correlated with the viscosity of the lower part of the mantle and that the viscosity profile is characterized by a decrease in the lower part of the upper mantle (about 10 20 –2  x  10 20 Pa s) and by an increase (about 10 23 –2  x  10 23 Pa s) at the top of the lower mantle (between 670 and 1150 km). The viscosity of the mantle below 1150 km depth is well estimated in our Monte Carlo search and is about 10 22 –4  x  10 22 Pa s.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 7
    Publication Date: 2016-02-26
    Description: Full waveform inversion using the conventional L 2 distance to measure the misfit between seismograms is known to suffer from cycle skipping. An alternative strategy is proposed in this study, based on a measure of the misfit computed with an optimal transport distance. This measure allows to account for the lateral coherency of events within the seismograms, instead of considering each seismic trace independently, as is done generally in full waveform inversion. The computation of this optimal transport distance relies on a particular mathematical formulation allowing for the non-conservation of the total energy between seismograms. The numerical solution of the optimal transport problem is performed using proximal splitting techniques. Three synthetic case studies are investigated using this strategy: the Marmousi 2 model, the BP 2004 salt model, and the Chevron 2014 benchmark data. The results emphasize interesting properties of the optimal transport distance. The associated misfit function is less prone to cycle skipping. A workflow is designed to reconstruct accurately the salt structures in the BP 2004 model, starting from an initial model containing no information about these structures. A high-resolution P -wave velocity estimation is built from the Chevron 2014 benchmark data, following a frequency continuation strategy. This estimation explains accurately the data. Using the same workflow, full waveform inversion based on the L 2 distance converges towards a local minimum. These results yield encouraging perspectives regarding the use of the optimal transport distance for full waveform inversion: the sensitivity to the accuracy of the initial model is reduced, the reconstruction of complex salt structure is made possible, the method is robust to noise, and the interpretation of seismic data dominated by reflections is enhanced.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
    Publication Date: 2016-02-03
    Description: Extracting detailed earth information from an ensemble of seismic traces is a challenge facing full-waveform inversion. So far, success on synthetic and real data has been accomplished primarily for the twin purposes of complex structural imaging and geologic interpretation. An ongoing issue for the seismic-imaging community, in addition to building high-resolution images, is the reliable extraction of acoustic and shear velocities, anisotropic parameters, quality factors, and density. Such extractions, performed at the seismic resolution scale, should help greatly with quantitative interpretation and estimation of rock properties. A step toward this goal is described here. A generic rock-physics model is assumed, which upscales microscale rock-physics properties to mesoscale (effective-medium) poroelastic quantities to be recovered from macroscale estimates of seismic attributes. It is shown on simple synthetic examples that quantitative multiparameter reconstruction, when it is possible, can reduce ambiguities in mesoscale parameter estimation dramatically, using a semiglobal search. Successful estimation of these effective-medium quantities will narrow the range of possible rock-physics estimations to be considered for seismic imaging target zones. For example, estimating the P-wave quality factor along with P-wave velocity from full-waveform inversion is shown to change the estimation of mesoscale parameters significantly, assuming that the upscaling of the rock-physics model and the recovered macroscale parameters are well constrained. In addition, shear-wave information is shown to be crucial for pressure-saturation discrimination. The inferred information at the reservoir level, resulting from full-waveform inversion and subsequent mesoscale estimation, can be useful for reservoir characterization.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
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  • 9
    Publication Date: 2016-02-27
    Description: Full waveform inversion using the conventional L 2 distance to measure the misfit between seismograms is known to suffer from cycle skipping. An alternative strategy is proposed in this study, based on a measure of the misfit computed with an optimal transport distance. This measure allows to account for the lateral coherency of events within the seismograms, instead of considering each seismic trace independently, as is done generally in full waveform inversion. The computation of this optimal transport distance relies on a particular mathematical formulation allowing for the non-conservation of the total energy between seismograms. The numerical solution of the optimal transport problem is performed using proximal splitting techniques. Three synthetic case studies are investigated using this strategy: the Marmousi 2 model, the BP 2004 salt model, and the Chevron 2014 benchmark data. The results emphasize interesting properties of the optimal transport distance. The associated misfit function is less prone to cycle skipping. A workflow is designed to reconstruct accurately the salt structures in the BP 2004 model, starting from an initial model containing no information about these structures. A high-resolution P -wave velocity estimation is built from the Chevron 2014 benchmark data, following a frequency continuation strategy. This estimation explains accurately the data. Using the same workflow, full waveform inversion based on the L 2 distance converges towards a local minimum. These results yield encouraging perspectives regarding the use of the optimal transport distance for full waveform inversion: the sensitivity to the accuracy of the initial model is reduced, the reconstruction of complex salt structure is made possible, the method is robust to noise, and the interpretation of seismic data dominated by reflections is enhanced.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
    Publication Date: 2016-10-08
    Description: Three-dimensional implementations of reverse time migration (RTM) and full-waveform inversion (FWI) require efficient schemes to access the incident field to apply the imaging condition of RTM or build the gradient of FWI. Wavefield reconstruction by reverse propagation using final snapshot and saved boundaries appears quite efficient but unstable in attenuating media, whereas the checkpointing strategy is a stable alternative at the expense of increased computational cost through repeated forward modeling. We have developed a checkpointing-assisted reverse-forward simulation (CARFS) method in the context of viscoacoustic wave propagation with a generalized Maxwell body. At each backward reconstruction step, the CARFS algorithm makes a smart decision between forward modeling using checkpoints and reverse propagation based on the minimum time-stepping cost and an energy measure. Numerical experiments demonstrated that the CARFS method allows accurate wavefield reconstruction using less timesteppings than optimal checkpointing, even if seismic attenuation is very strong. For RTM and FWI applications involving a huge number of independent sources and/or applications on architectures with limited memory, CARFS will provide an efficient tool with adequate accuracy in practical implementation.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
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