Estimation of azimuthally varying attenuation from surface seismic data

Observing the azimuthally varying seismic attenuation in data that show azimuthal velocity anisotropy could contribute not only to the interpretation of the subsurface symmetry systems, but also to the characterization of its physical parameters. In this paper, we estimate azimuthal variations of the P-wave effective quality factor (Q) from field surface seismic data. We also provide an interpretation of our results taking into account the NMO ellipse parameters measured from the data, and potential bias caused by systematic noise. By assuming that Q is frequency independent, and the medium at each particular azimuth the medium is laterally homogeneous, we use the spectral ratio method and a regularized linear inversion scheme to estimate the quality factor in azimuth-sectored data. The regularization parameters are chosen by a χ criterion that is based on estimates of the variance in the field data. Tests on synthetic data show that this regularized inversion provides robust estimates of Q for signal-to-noise ratios lower than those observed in the data. Application of this methodology to P-wave data from the East Decatur Field in Texas yields non-negligible azimuthal variations in Q. The azimuthal signature of attenuation appears to be consistent with the effective NMO ellipse from the same interface. However, data residuals show non-random structures that suggest a strong systematic component to the noise. We provide a brief analysis of scattering-related absorption and of frequency imprints of source-receiver arrays as possible sources of systematic noise.