87 © EDP Sciences, 2026 DOI: https://doi.org/10.1051/978-2-7598-3934-6.c005 QUAL I TÉ GÉOPHYSIQUEAPPLIQUÉE Geophysical methods J.-L. Mari Studies conducted at the Hydrogeological Experimental Site (HES) focus mainly on the Dogger Aquifer. Conventional hydrogeological surveys have investigated the site, which was also subjected to geophysical investigations both from the surface and in wells. These studies include conventional hydrological surveys and geophysical investigations, both from the surface and in wells. On the site, 35 boreholes have been drilled (Fig. 1). In 2004, 3D seismic data were recorded to obtain a 3D velocity model in depth. A vertical seismic profile (VSP) was recorded in borehole C1 to perform the timeto-depth conversion of the seismic block. An acoustic tool was run in boreholes C1, MP5, MP6, M08, and M09 to record full waveform acoustic data and compute velocity logs used as constraints for converting seismic amplitudes in pseudo-velocities during the inversion process. The resulting 3D seismic pseudo-velocity block revealed three main high-porosity, presumably water-producing layers, at depths of 35-40, 85-87, and 110-115 m that were identified as karstic levels. Multi-borehole logging investigations were carried out at the HES site (Audouin et al., 2008). To confirm the presence of karstic layers, both acoustic and seismic borehole data were collected from several boreholes. In the low-frequency range (10–150 Hz), Vertical Seismic Profile (VSP) data were acquired using a hydrophone sensor, which is particularly sensitive to Stoneley waves — commonly used to detect subsurface discontinuities such as fractures or faults. In the high-frequency range (1–20 kHz), full waveform acoustic logs were recorded to provide a detailed characterization of the formations. 5
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