Acoustic global-local full-waveform inversion for P-wave velocity estimation of near-surface seismic data acquired in Luni, Italy

摘要

In this work, we describe an experiment concerning global-local full-waveform inversion, carried out on a P-wave seismic reflection profile that was acquired at Luni, an archaeological site in Italy. The global full-waveform inversion makes use of a two-grid genetic algorithm scheme and recorded refraction and diving waves, to build an initial velocity model of the subsurface. Two important pieces of a priori information which help to better constrain the inversion results are the refraction velocity model and the Dix-converted semblance velocity field obtained from time processing. A good match between observed and predicted data allows us to use the estimated velocity field as the starting point for a local, gradient-based full-waveform inversion that inverts the recorded data (except the surface waves). The final estimated velocity field shows two main discontinuities: one is very shallow and related to the refractor velocity model used and the other corresponds to the strongest reflection event observed in the pre-stack depth-migrated section, at a depth of 100 m. The pre-stack depth-migrated common image gathers provide evidence of a good horizontal alignment of this reflection, indicating an accurate velocity estimation down to 100 m depth that corresponds to the maximum offset used in the acquisition.