Reflection moveout of SV-waves in transversely isotro-pic media with a vertical symmetry axis (VTI media) can provide valuable information about the model parameters and help to overcome the ambiguities in the inversion of P-wave data. Here, to develop a foundation for shear-wave migration velocity analysis, we study SV-wave image gathers obtained after prestack depth migration.

The key issue, addressed using both approximate analytic results and Kirchhoff migration of synthetic data, is whether long-spread SV data can constrain the shear-wave vertical velocity

VS0
and the depth scale of VTI models. For homogeneous media, the residual moveout of horizontal SV events on image gathers is close to hyperbolic and depends just on the NMO velocity
Vnmo
out to offset-to-depth ratios of about 1.7. Because
Vnmo
differs from
VS0
, flattening moderate-spread gathers of SV-waves does not ensure the correct depth of the migrated events.

The residual moveout rapidly becomes nonhyperbolic as the offset-to-depth ratio approaches two, with the migrated depths at long offsets strongly influenced by the SV-wave anisotropy parameter σ. Although the combination of

Vnmo
and σ is sufficient to constrain the vertical velocity
VS0
and reflector depth, the tradeoff between σ and the Thomsen parameter ∊ on long-spread gathers causes errors in time-to-depth conversion. The residual moveout of dipping SV events is also controlled by the parameters
Vnmo
, σ, and ∊, but in the presence of dip, the contributions of both σ and ∊ are significant even at small offsets.

For factorized v(z) VTI media with a constant SV-wave vertical-velocity gradient

kzs
⁠, flattening of horizontal events for a range of depths requires the correct NMO velocity at the surface, the gradient
kzs
, and, for long offsets, the parameters σ and ∊. On the whole, the nonnegligible uncertainty in the estimation of reflector depth from SV-wave moveout highlights the need to combine P- and SV-wave data in migration velocity analysis for VTI media.

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