Coarse-layer stripping of vertically variable azimuthal anisotropy from shear-wave data

Alford rotation analysis of 2C x 2C shear-wave data (two source components, two receiver components) for azimuthal anisotropy is valid only when the o rientation of that azimuthal anisotropy is invariant with depth. The Winter stein and Meadows method of layer stripping vertical seismic profiling (VSP ) data relaxes this restriction for coarse-layer variation of the orientati on of the anisotropy. Here we present a tensor generalization of the conven tional convolutional model of scalar wave propagation and use it to derive generalizations of Winterstein and Meadows layer stripping, valid for 2C x 2C data and for the restricted 2C-only case, in the VSP and reflection cont exts; In the 2C x 2C VSP application, the result reduces to that of Winters tein and Meadows in the case where both fast and slow shear modes have the same attenuation and dispersion; otherwise, a balancing of mode spectra and amplitudes is required. The 2C x 2C reflection result differs from the 2C x 2C VSP result, since two applications of the mode-balancing and mode-adva nce operations are required (since the waves travel upas well as down). App lication to a synthetic data set confirms these results. The 2C x 2C reflec tion algorithm enables the exploration for sweet spots of high fracture int ensity ahead of the bit without the restrictive assumption that the anisotr opy orientation is depth invariant.