Multiscale geophysical characterization of an unstable rock mass

Hazard mitigation from rockfalls and landslides is a priority in densely populated areas. A proper characterization of the inner structure of the rock mass is key to the comprehension of the mechanisms enhancing the slope instabilities. To this aim multi-scale geophysical methods can provide a novel and valuable tool for an high-resolution imaging of the internal structure of the rock mass and unique constraints on the physical state of the medium. We present here a cross-hole seismic tomography survey coupled with laboratory ultrasonic velocity measurements and physical properties determination on rock samples to characterize the damaged and potentially unstable granitic cliff of Madonna del Sasso (NW Italy). Results allowed to achieve two main advances, in terms of obtaining: i) a lithological interpretation of the velocity field obtained at the site, ii) a systematic correlation of the measured velocities with physical properties (density and porosity) and macroscopic features of the granite (weathering and anisotropy) of the cliff. Geophysical tests revealed to be crucial for the imaging at depth of the main fractures affecting the cliff and for the understanding of the variations in the seismic velocity between altered and intact rock to be used in further microseismic monitoring studies.