ESTIMATION OF ELASTIC PARAMETERS FROM AVO EFFECTS IN THE TAU-P DOMAIN

A quantitative AVO algorithm suitable for media with slow lateral para meter variations is developed. The method is based on a target-oriente d inversion scheme for estimation of elastic parameters in a locally h orizontally stratified medium. The algorithm uses band-limited PP refl ection coefficients in the tau-p domain to estimate P- and S-wave velo cities, densities and layer thicknesses. To obtain these reflection co efficients, a pre-processing involving the Radon transform and multipl e attenuation is necessary. Furthermore, a macromodel for the velociti es above the target zone must be found prior to the inversion. Various inversion tests involving synthetic data with white Gaussian noise an d modelling errors that are likely to occur in conjunction with real d ata have been performed. In general, the inversion algorithm is fairly robust, since it is able to reproduce the main features of the refere nce model: main interface locations and relative contrasts in the thre e unknown layer parameters are recovered. From a test combining the ef fect of source directivity, one thin layer and 20% white Gaussian nois e, it was found that neglect of the source directivity in the inversio n caused the largest errors in the estimates. This indicates that it i s very important either to eliminate the source directivity in a prepr ocessing step, or to take the directivity into account in the present algorithm. Despite these problems it was concluded that the inversion algorithm was able to reproduce the main features of the reference mod el.