ABSTRACT

The seismic refraction survey, routinely used to obtain information on subsurface geology, has a limited use in the foreshore zone. We have evaluated a nonstandard approach to acquire seismic data in the backshore-foreshore area, joining up land and marine seismic data. The innovative part was the acquisition of a continuous seismic profile that allowed the recording of high-resolution data in a transition zone (TZ) to establish an integrated approach for improving the land-marine seismic model in areas characterized by a complex near surface geology. To achieve this objective, two seismic tests were carried out along the beaches of the Tyrrhenian islands of Procida and Ventotene. We defined the P-wave VP and S-wave velocities VS with depth by integrating the tomography of the refracted first arrivals (VP velocities versus depth) with the inversion of the phase velocities dispersion curves extracted from the surface waves (1D VS velocities models). Working with both seismic methods allowed us to overcame the limitations of each approach and to compare and check the obtained results. The velocity models enabled resolution of the near-surface velocity variations and definition of refractors down to a maximum depth of 40 m below ground level. This has provided useful insights to map the 2D bedrock surface and to evaluate ground stiffness and dynamic behavior of soil. Our study, aiming to demonstrate the feasibility of high-resolution seismic surveys in the land-sea TZ, proved that the use of a marine streamer connected to land cable, was a powerful tool to define different subsoil structures to assist with future planning (coastal management) of these areas.

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