Passive seismic monitoring of potentially unstable rock masses

Passive seismic monitoring data acquired at the potentially unstable granitic cliff of Madonna del Sasso (NW Italy) are presented in this work. The spectral content of seismic noise systematically highlighted clear energy peaks on the unstable sector, interpreted as resonant frequencies of the investigated volume. Ground motion at these frequencies was found to be controlled by the main fractures observed at the site and numerical modelling is currently under development for geomechanical and modal analysis of the site. Both spectral analysis and cross-correlation of seismic noise showed seasonal reversible variations related to temperature fluctuations. No irreversible changes, resulting from serious damage processes, were detected during the monitored period. Classification and location of microseismic events had also been attempted but resulted challenging due to the complex structural and morphological setting of the cliff.