Waveform inversion of marine reflection seismograms for P impedance and Poisson's ratio

The estimation of the elastic properties of the crust from surface seismic recordings is of great importance for an understanding of the lithology and the detection of mineral resources. Although in marine reflection experiments only P waves are recorded, information on shear properties of the medium is contained in the reflection amplitudes recorded at different distances from the source. Being able to estimate both dilatational and shear properties gives stronger constraints on the lithology. It is therefore desirable to recover both types of elastic parameters from multi-offset seismograms. In the real-data example presented here, the amplitude of the reflections cannot be explained by one parameter related to the dilatational properties (P impedance) only, when trying to minimize the least-squares fit between synthetic and real multi-offset seismograms. When adding an additional parameter related to the shear properties (Poisson's ratio), the fit between synthetic and real seismograms improves. Synthetic-waveform-fitting experiments underline the possibility of recovering Poisson's ratio when the P-impedance model is well known from fitting waveforms recorded at small offsets. In the real-data example, the resulting models for P impedance and Poisson's ratio are anticorrelated in most depth regions, but are correlated in a particular depth region, indicating a sudden change in lithology.