Applying waveform inversion to wide-angle seismic surveys

Multi-scale frequency-domain acoustic waveform inversion was applied to refraction and wide-angle reflection seismic surveys of the upper crust across the plate-bounding San Andreas Fault, California, and the Chesapeake Bay impact structure, Virginia. This paper presents and compares the data, the preconditioning, and different inversion strategies. The inversions start at 3 Hz, and they are stopped at 15 Hz due to increasing non-linear artifacts. The resulting waveform models show a significant improvement in resolution compared to the traveltime starting models, but they do not achieve the resolution demonstrated in synthetic studies. Possible reasons for this limitation are discussed, especially the possibility of insufficient bandwidth, and the effect of normalizing amplitudes. The comparison of results from normalized-amplitude and true-amplitude waveform inversions indicates that amplitudes do not strongly constrain the velocity structure. Phase coherency weights are presented that mitigate the impact of noise. Maps of phase misfits provide a quantitative overview of the data residuals and some insight into the spatial distribution of errors. They are helpful for monitoring the progress of the inversion, and for determining if and when it must be stopped.