Gradient computation for VTI acoustic wavefield tomography

Vladimir Li, Hui Wang, Ilya Tsvankin, Esteban Diaz, Tariq Ali Alkhalifah

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a pseudospectral operator that employes a separable approximation of the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified stack-power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations. Whereas the kernels computed with the two wave-equation operators are similar, the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show that the modified stack-power objective function produces cleaner gradients than the more conventional DSO operator.
Original languageEnglish (US)
Title of host publicationSEG Technical Program Expanded Abstracts 2016
PublisherSociety of Exploration Geophysicists
Pages419-424
Number of pages6
DOIs
StatePublished - Sep 2016

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