Extended images obtained from reverse time migration (RTM) contain information about the accuracy of the velocity field and subsurface illumination at different incidence angles. Here, we evaluate the influence of errors in the anisotropy parameters on the shape of the residual moveout (RMO) in P-wave RTM extended images for VTI (transversely isotropic with a vertical symmetry axis) media. Using the actual spatial distribution of the zero-dip NMO velocity (Vnmo), which could be approximately estimated by conventional techniques, we analyze the extended images obtained with distorted fields of the parameters η and δ. Differential semblance optimization (DSO) and stack-power estimates are employed to study the sensitivity of focusing to the anisotropy parameters. We also build angle gathers to facilitate interpretation of the shape of RMO in the extended images. The results show that the signature of η is dip-dependent, whereas errors in δ cause defocusing only if that parameter is laterally varying. Hence, earlier results regarding the influence of η and δ on reflection moveout and migration velocity analysis remain generally valid in the extended image space for complex media. The dependence of RMO on errors in the anisotropy parameters provides essential insights for anisotropic wavefield tomography using extended images.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): CRG3
Acknowledgements: We are grateful to Paul Sava (CWP) and members of the A(nisotropy)
and i(maging) teams at CWP for useful discussions. Model 2
represents a modified version of the TTI model created by
Hemang Shah of BP (http://www.freeusp.org/2007_BP_Ani_Vel_
Benchmark/). This publication is based upon work supported by
the Consortium Project on Seismic Inverse Methods for Complex
Structures at CWP and the King Abdullah University of Science
and Technology (KAUST) Office of Sponsored
Research (OSR) under Award No. OCRF-2014-
CRG3-32140407/ORS#2230. The reproducible
numeric examples in this paper use the Madagascar
open-source software package (Fomel et al.,
2013a) freely available from http://www.ahay.org.