Evidence of unstable rock cliffs from vibrational behavior: challenges in coupling engineering-geological and geophysical approaches

Abstract

Over the last decades, engineering-geology has increasingly made use of multidisciplinary approaches aimed at detecting physical-mechanical characteristics of the subsoil in the near surface, to better understand and monitor the dynamics of natural processes as potential causes of natural risk. Geophysical investigations by passive seismic in the near surface became over time a fundamental tool to interpretate the vibrational behaviors of rock volumes, already displaced by physical discontinuities (i.e. rock mass joints). The frequencies of oscillation, amplified by dislodged blocks, are polarized in specific directions, and related to eigenmodes which depend on their degrees of freedom, mass, stiffness and damping coefficient. On the other hand, the superposition of soft soil on bedrock induces stratigraphic amplification which may not be polarized if they occur in properly one-dimensional contexts. This contribution focuses on the aforementioned investigation techniques, through a review of case studies which allowed learning their diagnostic potential and, at the same time, conceptualizing their functionality and adaptability (under certain representativeness constraints) to different morphoevolutionary contexts. The hazard zoning for rock landslide, which have been created to date by these techniques, appear to be fully integrated into thematic maps on active landslide processes and related spatial distribution, seismic microzonation maps and related areas of instability, residual risk perimeter maps aimed at preventing access or usability of urbanized areas.