Terrestrial remote sensing and microtremor measurements for the study of the vibrations of a rock mass with large underground cavities

This note describes an experimental study aimed at evaluate the vibration properties of a limestone rock vault, subjected to the forcing action produced by an intense vehicular traffic. The site of study occupies an area of about 3,000 m2. The subsoil of the site is characterised by shallow underground cavities due to the past quarry activities. Ambient vibration measurements were done by means of seismometer stations placed on the ground surface. Microtremor stations were arranged above the cavity and in the surrounding area. An innovative coherent radar sensor was installed inside the underground cavity in order to measure time series of displacement related to different reflector points located on the internal surface of the vault. The experimental vibration properties were derived by means of frequency analyses of both seismic and interferometric data in order to compare the results achieved by using the seismic transducers and the unconventional microwave sensor. Furthermore the preliminary results of numerical simulations were discussed.