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

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.