A seismic survey was carried out in the area of a salt mine area with the principal aims of identifying potential zones of subsidence, and the locations and sizes of the water filled cavities generated during salt extraction. Several high resolution 2-D seismic profiles were acquired and interpreted, allowing a detailed definition of the main stratigraphic units as well as the general geological setting. However, cavity identification and location remained uncertain. For improving the interpretation, a 2-D model was developed in order to characterize the seismic signature of these cavities. The model represents the cross-section of a brine filled cavity imbedded in a two layer half-space, and reproduces the situation at a site which was well known from well data and sonar investigation. Wave propagation was simulated by solving numerically the scalar full wave equation with the Chebyshev spectral element method. The dynamics of this model, as well as the analysis and characterization of the seismic signature of the cavity in a stacked section, are illustrated and explained in the paper. Synthetic results are directly compared with the real data, and a critical analysis of the detectability of water-filled cavities is given. Among the results, it was observed that reflection and diffraction from the cavity bottom is stronger than that from the cavity top; however, the diffraction hyperbolas from cavity top and bottom, which would usually be the strongest evidence for the presence of a cavity, may often be hidden in real data by seismic noise, making detection difficult. Finally, a further seismic stacked section acquired at a different site is discussed in the light of the experience acquired.