Ambient vibrations recorded on potentially-unstable rock slopes show that the temporal variations in the
spectral content and in the correlation of seismic noise can be related to both reversible and irreversible
changes within the rock mass. In this work, we analyzed the seismic recordings acquired at the potentiallyunstable
granitic cliff of Madonna del Sasso (NW Italy) from October 2013 to November 2014.
The spectral content of noise systematically highlighted clear energy peaks at specific frequencies on the
most unstable sector, interpreted as resonant frequencies of the investigated volume. Horizontal ground
motion at the fundamental frequency was moreover found to be orthogonal to the main fractures observed
at the site and consequently parallel to the potential direction of collapse. Cross-correlation was computed
between the recordings of the sensors placed in the prone-to-fall compartment and a stable reference
station.
Both the temporal variations of the resonant frequencies and the results of cross-correlation showed
seasonal reversible variations related to temperature fluctuations. No irreversible changes, resulting from
damage processes within the rock mass, were detected during the monitored period