## Search

Now showing items 1-10 of 13

JavaScript is disabled for your browser. Some features of this site may not work without it.

AuthorStoffa, Paul L. (5)Chu, Chunlei (3)Kamath, Nishant (3)Seif, Roustam (3)Tsvankin, Ilya (3)View MoreJournalSEG Technical Program Expanded Abstracts 2009 (4)SEG Technical Program Expanded Abstracts 2014 (3)SEG Technical Program Expanded Abstracts 2011 (2)SEG Technical Program Expanded Abstracts 2012 (2)SEG Technical Program Expanded Abstracts 2016 (1)View MorePublisher

Society of Exploration Geophysicists (13)

Subjectelastic (2)full-waveform inversion (2)VTI (2)Wave propagation (2)2D (1)View MoreType
Conference Paper (13)

Year (Issue Date)2017 (1)2016 (1)2014 (3)2012 (8)Item AvailabilityMetadata Only (13)

Now showing items 1-10 of 13

- List view
- Grid view
- Sort Options:
- Relevance
- Title Asc
- Title Desc
- Issue Date Asc
- Issue Date Desc
- Submit Date Asc
- Submit Date Desc
- Results Per Page:
- 5
- 10
- 20
- 40
- 60
- 80
- 100

Born reflection kernel analysis and wave-equation reflection traveltime inversion in elastic media

Wang, Tengfei; Cheng, Jiubing (SEG Technical Program Expanded Abstracts 2017, Society of Exploration Geophysicists, 2017-08-17) [Conference Paper]

Elastic reflection waveform inversion (ERWI) utilize the reflections to update the low and intermediate wavenumbers in the deeper part of model. However, ERWI suffers from the cycle-skipping problem due to the objective function of waveform residual. Since traveltime information relates to the background model more linearly, we use the traveltime residuals as objective function to update background velocity model using wave equation reflected traveltime inversion (WERTI). The reflection kernel analysis shows that mode decomposition can suppress the artifacts in gradient calculation. We design a two-step inversion strategy, in which PP reflections are firstly used to invert P wave velocity (Vp), followed by S wave velocity (Vs) inversion with PS reflections. P/S separation of multi-component seismograms and spatial wave mode decomposition can reduce the nonlinearity of inversion effectively by selecting suitable P or S wave subsets for hierarchical inversion. Numerical example of Sigsbee2A model validates the effectiveness of the algorithms and strategies for elastic WERTI (E-WERTI).

Elastic FWI for VTI media: A synthetic parameterization study

Kamath, Nishant; Tsvankin, Ilya; Diaz, Esteban (SEG Technical Program Expanded Abstracts 2016, Society of Exploration Geophysicists, 2016-09) [Conference Paper]

A major challenge for multiparameter full-waveform inversion (FWI) is the inherent trade-offs (or cross-talk) between model parameters. Here, we perform FWI of multicomponent data generated for a synthetic VTI (transversely isotropic with a vertical symmetry axis) model based on a geologic section of the Valhall field. A horizontal displacement source, which excites intensive shear waves in the conventional offset range, helps provide more accurate updates to the SV-wave vertical velocity. We test three model parameterizations, which exhibit different radiation patterns and, therefore, create different parameter trade-offs. The results show that the choice of parameterization for FWI depends on the availability of long-offset data, the quality of the initial model for the anisotropy coefficients, and the parameter that needs to be resolved with the highest accuracy.

Diffraction imaging and velocity analysis using oriented velocity continuation

Decker, Luke; Fomel, Sergey (SEG Technical Program Expanded Abstracts 2014, Society of Exploration Geophysicists, 2014-08-05) [Conference Paper]

We perform seismic diffraction imaging and velocity analysis by separating diffractions from specular reflections and decomposing them into slope components. We image slope components using extrapolation in migration velocity in time-space-slope coordinates. The extrapolation is described by a convection-type partial differential equation and implemented efficiently in the Fourier domain. Synthetic and field data experiments show that the proposed algorithm is able to detect accurate time-migration velocities by automatically measuring the flatness of events in dip-angle gathers.

Elastic full-waveform inversion of transmission data in 2D VTI media

Kamath, Nishant; Tsvankin, Ilya (SEG Technical Program Expanded Abstracts 2014, Society of Exploration Geophysicists, 2014-08-05) [Conference Paper]

Full-waveform inversion (FWI) has been implemented mostly for isotropic media, with extensions to anisotropic models typically limited to acoustic approximations. Here, we develop elastic FWI for transmitted waves in 2D heterogeneous VTI (transversely isotropic with a vertical symmetry axis) media. The model is parameterized in terms of the P- and S-wave vertical velocities and the P-wave normal-moveout and horizontal velocities. To test the FWI algorithm, we introduce Gaussian anomalies in the Thomsen parameters of a homogeneous VTI medium and perform FWI of transmission data for different configurations of the source and receiver arrays. The inversion results strongly depend on the acquisition geometry and the aperture because of the parameter trade-offs. In contrast to acoustic FWI, the elastic inversion helps constrain the S-wave vertical velocity, which for our model is decoupled from the other parameters.

Sensitivity analysis for elastic full-waveform inversion in VTI media

Kamath, Nishant; Tsvankin, Ilya (SEG Technical Program Expanded Abstracts 2014, Society of Exploration Geophysicists, 2014-08-05) [Conference Paper]

Multiparameter full-waveform inversion (FWI) is generally nonunique, and the results are strongly influenced by the geometry of the experiment and the type of recorded data. Studying the sensitivity of different subsets of data to the model parameters may help in choosing an optimal acquisition design, inversion workflow, and parameterization. Here, we derive the Fréchet kernel for FWI of multicomponent data from a 2D VTI (tranversely isotropic with a vertical symmetry axis) medium. The kernel is obtained by linearizing the elastic wave equation using the Born approximation and employing the asymptotic Green's function. The amplitude of the kernel (‘radiation pattern’) yields the angle-dependent energy scattered by a perturbation in a certain model parameter. The perturbations are described in terms of the P- and S-wave vertical velocities and the P-wave normal-moveout and horizontal velocities. The background medium is assumed to be homogeneous and isotropic, which allows us to obtain simple expressions for the radiation patterns corresonding to all four velocities. These patterns help explain the FWI results for multicomponent transmission data generated for Gaussian anomalies in the Thomsen parameters inserted into a homogeneous VTI medium.

A parallel sweeping preconditioner for frequency-domain seismic wave propagation

Poulson, Jack; Engquist, Björn; Li, Siwei; Ying, Lexing (SEG Technical Program Expanded Abstracts 2012, Society of Exploration Geophysicists, 2012-10-25) [Conference Paper]

We present a parallel implementation of Engquist and Ying's sweeping preconditioner, which exploits radiation boundary conditions in order to form an approximate block LDLT factorization of the Helmholtz operator with only O(N4/3) work and an application (and memory) cost of only O(N logN). The approximate factorization is then used as a preconditioner for GMRES, and we show that essentially O(1) iterations are required for convergence, even for the full SEG/EAGE over-thrust model at 30 Hz. In particular, we demonstrate the solution of said problem in a mere 15 minutes on 8192 cores of TACC's Lonestar, which may be the largest-scale 3D heterogeneous Helmholtz calculation to date. Generalizations of our parallel strategy are also briefly discussed for time-harmonic linear elasticity and Maxwell's equations.

Prestack first-break traveltime tomography using the double-square-root eikonal equation

Li, Siwei; Fomel, Sergey; Vladimirsky, Alexander (SEG Technical Program Expanded Abstracts 2012, Society of Exploration Geophysicists, 2012-10-25) [Conference Paper]

Traveltime tomography with shot-based eikonal equation fixes shot positions then relies on inversion to resolve any contradicting information between independent shots and achieve a possible cost-function minimum. On the other hand, the double-square-root (DSR) eikonal equation that describes the whole survey, while providing the same first-arrival travel-times, allows not only the receivers but also the shots to change position and therefore leads to faster convergence in tomo-graphic inversion. The DSR eikonal equation can be solved by a version of the fast-marching method (FMM) with special treatment for its singularity at horizontally traveling waves. For inversion, we use an upwind finite-difference scheme and the adjoint-state method to avoid explicit calculation of Fréchet derivatives. The proposed method generalizes to the 3D case straightforwardly.

Seismic wave propagation in fractured media: A discontinuous Galerkin approach

De Basabe, Jonás D.; Sen, Mrinal K.; Wheeler, Mary F. (SEG Technical Program Expanded Abstracts 2011, Society of Exploration Geophysicists, 2012-05-25) [Conference Paper]

We formulate and implement a discontinuous Galekin method for elastic wave propagation that allows for discontinuities in the displacement field to simulate fractures or faults using the linear- slip model. We show numerical results using a 2D model with one linear- slip discontinuity and different frequencies. The results show a good agreement with analytic solutions. © 2011 Society of Exploration Geophysicists.

Separate P- and SV-wave equations for VTI media

Pestana, Reynam C.; Ursin, Bjørn; Stoffa, Paul L. (SEG Technical Program Expanded Abstracts 2011, Society of Exploration Geophysicists, 2012-05-25) [Conference Paper]

In isotropic media we use the scalar acoustic wave equation to perform reverse time migration RTM of the recorded pressure wavefleld data. In anisotropic media P- and SV-waves are coupled and the elastic wave equation should be used for RTM. However, an acoustic anisotropic wave equation is often used instead. This results in significant shear wave energy in both modeling and RTM. To avoid this undesired SV-wave energy, we propose a different approach to separate P- and SV-wave components for vertical transversely isotropic VTI media. We derive independent pseudo-differential wave equations for each mode. The derived equations for P- and SV-waves are stable and reduce to the isotropic case. The equations presented here can be effectively used to model and migrate seismic data in VTI media where ε - δ is small. The SV-wave equation we develop is now well-posed and triplications in the SV wavefront are removed resulting in stable wave propagation. We show modeling and RTM results using the derived pure P-wave mode in complex VTI media and use the rapid expansion method REM to propagate the waveflelds in time. © 2011 Society of Exploration Geophysicists.

Rapid expansion method (REM) for time-stepping in reverse time migration (RTM)

Pestana, Reynam C.; Stoffa, Paul L. (SEG Technical Program Expanded Abstracts 2009, Society of Exploration Geophysicists, 2012-03-22) [Conference Paper]

We show that the wave equation solution using a conventional finite-difference scheme, derived commonly by the Taylor series approach, can be derived directly from the rapid expansion method (REM). After some mathematical manipulation we consider an analytical approximation for the Bessel function where we assume that the time step is sufficiently small. From this derivation we find that if we consider only the first two Chebyshev polynomials terms in the rapid expansion method we can obtain the second order time finite-difference scheme that is frequently used in more conventional finite-difference implementations. We then show that if we use more terms from the REM we can obtain a more accurate time integration of the wave field. Consequently, we have demonstrated that the REM is more accurate than the usual finite-difference schemes and it provides a wave equation solution which allows us to march in large time steps without numerical dispersion and is numerically stable. We illustrate the method with post and pre stack migration results.

The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

By default, clicking on the export buttons will result in a download of the allowed maximum amount of items. For anonymous users the allowed maximum amount is 50 search results.

To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.