Automatic nonhyperbolic velocity analysis

The stacking of long-offset seismic data requires a nonhyperbolic traveltime function that depends on two-way traveltime, normal moveout (NMO) velocity and effective anellipticity. Based on a standard fractional approximation, a new parameterization in slowness-squared parameters provides optimal sampling of the NMO velocity and anellipticity. The automatic nonhyperbolic velocity analysis is performed with a normalized bootstrapped differential semblance (BDS) coherency estimator that leads to enhanced resolution in velocity spectra compared to differential semblance. Reflection wavelet centering inside time gates results in improved estimates of the two-way time and reduced bias in estimates of the NMO velocity and anellipticity. Generalized Dix equations give estimates of apparent interval thickness, velocity and anellipticity. The interval parameters will fit a homogeneous transversely isotropic medium with a vertical symmetry axis (a VTI medium) or an isotropic layer with a linear velocity gradient. T...

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