Geophysical Prospecting, 1996, 44, 427 -455 Linearized elastic parameter sectionsl BjornUrsin,2 Biorn Olav Ekren3 and Egil Tjiiland2 Abstract Contrasts in elastic parameters can be estimated directly from seismic data using offset-dependent information in the PP reflection coefficient. A linear approximation to the PP reflection coefficient including three coefficients is fitted to the data, and relative contrasts in various elastic parameters are obtained from linear combinations of the estimated coefficients.Linearized elastic parameter sectionsfor the contrasts in P-wave impedance, P-wave velocity, density, plane-wave modulus, and the changein bulk modulus and shear modulus normalized with the plane-wave modulus are estimated. If the averageP- to S-wave velocity ratio is known, linearized parameter sections including the contrast in the averageP- to S-wave velocity ratio and a fluid factor section can be computed. Applied to synthetic data, visual comparison of the estimated and true elastic parameter sections agree qualitatively, and the results are confirmed by an analysis of the standard deviation of the estimated parameters. The parameter sectionsobtained by inversion of a shallow seismic anomaly in the Barents Sea are promising, but the reliability is uncertain because neither well data nor regional trends are available. lntroduction Amplitude-versus-offset (AVO) analysis is based on offset- or angle-dependent reflection coefficients, and is successfully used as a qualitative tool for lithology and fluid prediction in many regions. AVO inversion, which is still in an early stage, is quantitative and estimates the elastic parameters in the subsurface. AVO inversion assumes that all offset- dependent amplitude effects, other than the reflection coefficient, are corrected for. In this case, at least theoretically, contrasts in elastic parameters can be estimated from seismic data. AVO inversion methods based on a linear approximation to the PP reflection coefficient result in weighted stacking schemes(Smith and Gidlow 1987; Ursin and Dahl 1990; Gidlow, Smith and Vail 1992).In general, AVO inversion is non-unique I Received January 1994, revision accepted June 1995. 2 University of Trondheim, The Norwegian Institute of Technology, Department of Petroleum Engineering and Applied Geophysics, S.P. Andersens vei 15,A., N-7034 Trondheim NTH, Norway 3 Statoil Research Center, Postuttak, N-7005 Trondheim, Norway. Formeriy at'. O 1996 European Association of Geoscientists & Engineers 427