WAVE-FORM INVERSION OF MARINE REFLECTION SEISMOGRAMS FOR P-IMPEDANCE AND POISSON RATIO

The estimation of the elastic properties of the crust from surface sei smic recordings is of great importance for an understanding of the lit hology and the detection of mineral resources. Although in marine refl ection experiments only P waves are recorded, information on shear pro perties of the medium is contained in the reflection amplitudes record ed at different distances from the source. Being able to estimate both dilatational and shear properties gives stronger constraints on the l ithology. It is therefore desirable to recover both types of elastic p arameters from multi-offset seismograms. In the real-data example pres ented here, the amplitude of the reflections cannot be explained by on e parameter related to the dilatational properties (P impedance) only, when trying to minimize the least-squares fit between synthetic and r eal multi-offset seismograms. When adding an additional parameter rela ted to the shear properties (Poisson's ratio), the fit between synthet ic and real seismograms improves. Synthetic-waveform-fitting experimen ts 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 impedan ce and Poisson's ratio are anticorrelated in most depth regions, but a re correlated in a particular depth region, indicating a sudden change in lithology.