Anisotropy signature in P-wave extended images for VTI media

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 residual moveout (RMO) in P-wave extended images obtained with RTM for VTI (transversely isotropic with a vertical symmetry axis) media. Assuming the actual spatial distribution of the zero-dip normal-moveout velocity, we analyze extended images computed with distorted fields of the parameters η and δ. Differential semblance optimization (DSO) and stack-power criteria are employed to study the sensitivity of focusing to the anisotropy parameters. The results show that the signature of η is dip-dependent, whereas errors in δ cause defocusing in extended images only if that parameter varies laterally. We also obtain and analyze the gradients of the DSO objective function with respect to the anisotropy parameters. The results of this work provide the foundation for anisotropic wavefield tomography operating with extended images. Summary Introduction The extended imaging condition retains information about the wavefield directionality and angle-dependent reflector illumination by preserving the spatial and/or temporal correlation lags in the output. For example, one can obtain space-lag (Rickett and Sava, 2002) or time-lag (Sava and Fomel, 2006) extended common-image gathers (CIG), which are computed at fixed horizontal coordinates.