Sensitivity study of seismic reflectionh-efraction data

The reliability of information obtained from surface seismic measurements is an important factor to be considered before one attempts to depth migrate or invert seismic data. The uniqueness of the retrieved model can only be achieved if the observed seismic data contain information on all the wavelengths of the Earth structure. In this study we investigated the sensitivity of model parameters obtainable from elastic multi-offset seismic data. We perturbed a background model, which was defined in terms of longitudinal and shear velocities and density, with quasi-sinusoidal perturbations. The reference and perturbed synthetic seismograms were calculated in the intercept time and slowness (7-p) domain. The seismic waveform misfit between these two synthetic seismograms computed in a least-squares sense was used as a quantitative measure of the sensitivity of model parameters. We found that middle-wavelength variations of model parameters are sensitive to critical-angle seismic data. This was further confirmed by using a 1-D waveform inversion. These results suggest that all wavelengths of model parameters can be retrieved from waveform analysis of seismic reflection/refraction data: the long wavelengths from traveltime data and the short to medium wavelengths from waveform analysis. The non-uniqueness associated with the information gap for middle wavelengths, as previously proposed for seismic reflection data, can therefore be avoided. Key words: P waves, sensitivity analysis, waveform inversion