Geophysical characterization of an unstable rock mass

A pre-requisite in rock mass stability analysis is to obtain the internal structure and the mechanical properties of the investigated rock mass with a reasonable degree of uncertainty. In this respect, geophysical methods can be profitably used as an imaging and characterization tool. Seismic methods are often more suitable because the measurements depend on the mechanical properties of the rock mass. The present paper presents the use of cross-hole seismic tomography in a site (Madonna del Sasso – NW Italy) affected by a rock instability phenomenon, highlighted by episodes of slow deformation recorded by standard measurement devices. Geophysical tests have been fundamental in imaging the fracturing state and the relative variation of seismic velocities between intact an altered rock and in defining the seismic velocity field of the rock mass, a basic prerequisite for the future planned microseismic monitoring step.