Velocity and VTI anisotropy scanning in multicomponent seismic data

Christopher O. Ogiesoba, James E. Gaiser, and Robert R. Stewart

ABSTRACT

We present a prestack method that scans for the average vertical-velocity ratio γ 0 , and the effective anisotropic parameter η, using a new converted-wave (PS) non-hyperbolic traveltime equation. We tested our method using a numerical data set generated in ANIVEC (a frequency-wave number modeling package). The procedure entails computing semblance as a function of three variables: the PS velocity Vps, γ 0 , and η. Results are displayed in 3D plots as a function of the PS zero-offset time tps0. We observe that the derived equation is valid for an offset-depth ratio of up to 1.5 for the tested model. There is a tradeoff in resolving η and the velocity ratio γ 0 since both parameters control far offset moveout. The accuracy of the scanning technique increases with depth. It is inaccurate at shallow depths where the offset-depth ratio is greater than 1.5. At deeper levels, where the offset-depth ratio is 1 to 1.5, the errors in scanned velocity ratio γ 0 and effective anisotropic parameter η, range from +9 to +10% and +0.2 to +8%, respectively.

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