• Applied Geophysics
• Down-Hole
• FWI
• MASW
• Refraction

This thesis research analyzed a flat area characterized by a geologically disconnected subsurface, where several seismic investigation methods were conducted. The primary objective of this study was to compare different seismic survey methods to assess their effectiveness, highlight their advantages and disadvantages, and understand their potential in subsurface analysis. The seismic data was acquired using 48 equally spaced receivers and 7 shots generated by a hammer and the acquisition was performed using the GeoExplorer software by Sara Electronic Instruments. The analytical process began with the inversion of the acquired data (carried out with the software Down-Hole by GeoStru), starting with the Down-Hole method. This technique, being an active seismic method, is highly reliable and serves as a valuable reference for comparison with other survey methods. At the same time, thanks to the lithostratigraphic column obtained from borehole coring, it was possible to determine the number of layers on which to base subsequent inversions, with particular emphasis on those performed using the Multichannel Analysis of Surface Waves (MASW). To validate the presence of lateral discontinuities in the subsurface, the data acquired at stations S1 and S7 were initially inverted (S1 is positioned at a distance of 5 metres from the first geophone, outside the geophonic array, while S7 is placed at a distance of 5 metres beyond the last geophone in the line, precisely beyond geophone number 48) confirming that the stratigraphy of the area is not characterized by planar and parallel layers but rather by marked lateral heterogeneity. Subsequently, Vs-Depth profiles obtained from MASW inversion, performed using the Geopsy software, were compared by imposing configurations with three, four, and five layers using both shot 1 (S1) and shot 7 (S7). Furthermore, to refine the subsurface interpretation, a P-wave tomography model was generated by inverting the times of the first arrivals picked up on the data acquired for seismic refraction using the SmartTomo software. The P-wave tomography and the results derived from the Down-Hole and the MASW inversions showed good consistency, further confirming the accuracy of the inverted models. Another phase of the analysis involved the application of Full Waveform Inversion (FWI), used in this case in a deterministic approach, starting from two different initial models: one derived from the Down-Hole survey and the other based on the MASW inversion method. The preliminary phase of this technique required an initial processing of the acquired data, which was subjected to trace-by-trace normalization and a low-pass filter. Additionally, the estimation of the wavelet from the pre-processed data was carried out, which was crucial for the subsequent inversion. Once this phase was completed, a starting model for FWI was created by extending the results of MASW and DH to 2D models, differing in both the number of layers and the shear wave velocity (Vs) values. The application of this technique allowed for the generation of velocity models for both S-waves (Vs) and P-waves (Vp), although in a near surface context the Vp is much less constrained by the seismic data compared to the Vs. A particularly relevant aspect concerns the applicability of Full Waveform Inversion to real data. Finally, to quantify the reliability of the obtained results, the Relative Percent Error (RPE) was calculated, both between the observed and the initial data and between the observed and the predicted data. The analysis conducted demonstrated that the use of this technique is effective and advantageous, provided that an appropriate starting model is chosen. In this context, the integration of FWI with other seismic investigation methodologies, such as the Down-Hole and MASW methods, proved to be particularly useful, with all the predicted models obtained through FWI that have some differences, which depend on the chosen starting point, but present coherent structures. In particular, the velocity profiles obtained with DH and MASW are pretty consistent with the velocities extracted from FWI solutions in correspondence of the Down-Hole location and the inverted shot positions (S1 and S7). Therefore, the study confirms the importance of combining different survey techniques to obtain a more comprehensive and reliable reconstruction of subsurface structures. The overall analysis highlighted that, despite each method having specific advantages and limitations, the comparison of different techniques represents an extremely useful approach for achieving a more accurate subsurface characterization. In particular, the consistency of the obtained results demonstrates that integrating multiple methods enhances geophysical interpretation, further confirming the reliability of the techniques employed in this study.