Linearized elastic parameter sections

Contrasts in the elastic parameters can be estimated directly from seismic data using offset dependent variations in the seismic reflection coefficients (AVO effects). The data are analyzed in time windows after a block NMO correction. The data are further corrected for residual NMO and offset-dependent geometrical spreading and average array effects. The final amplitude variation is estimated by a polynomial in the offset coordinate (Ursin and Ekren, 1992). The coefficients in the reflecticity polynomial are related to the relative changes or contrasts in the elastic parameters, assuming that these contrasts are small. The average P-wave velocity (interval velocity) is estimated from velocity analysis of the seismic data. Then the contrasts in P-wave inipedance, P-wave velocity, density, plane wave modulus and normalized contrasts in shear modulus and bulk modulus can be estimated. When also the average S-wave velocity function is known, contrasts in S-wave impedance, S-wave velocity, shear modulus, bulk modulus, and P- to S-wave velocity ratio can be computed. A fluid-factor (Smith and Gidlow, 1987) can also be estimated.