3D image of the subsoil from complementary seismic methods

Summary This study consists of a geophysical survey, aiming to characterize the soil from a mechanical point of view by determining seismic velocities and to propose a geomechanical soil model over the first 50 meters. The survey consists of complementary seismic methods: Passive tomography using ambient seismic noise cross-correlations (Sissterra method, Sixense) H / V method Seismic refraction and MASW The results of the different methods are coherent with each other and with geotechnical data obtained from boreholes. The survey allowed a complete geophysical investigation down to 80m and the highlight of the main geological features. In particular, the results of the passive tomography and H/V highlight a deepening that could be related to a sedimentary paleo-valley. The results from the active and passive seismic methods show a good correlation in velocity contrasts. They mainly indicate a horizon with strong lateral variations in Vp and Vs, probably related to water level and to the base of lithological contrast, presenting unstructured passages in the form of Quaternary paleo structures. The 3D measurement made it possible to delimit the most probable locations of these structures and highlight a velocity inversion at depth, probably due to clay passages.