[S03-5] Imaging of heterogeneities in the Earth with seismic scattered waves and ambient noise V

[S03-5-06] Characterization and monitoring of ambient vibrations of a rock slope close to collapse

^○Jan Burjanek¹, Donat Faeh² (1.Institute of Geophysics of the CAS, Prague, Czech Republic, 2.Swiss Seismological Service, ETH Zurich, Zurich, Switzerland)

We present the ambient vibration study of Alpe di Roscioro, a developing rock slope failure located above the village Preonzo in southern Switzerland. Following a major failure in May 2012 (volume ~210,000 m3), the remaining unstable rock mass (~140,000 m3) remains highly fractured and disrupted, and has been the subject of intensive monitoring. A small-aperture seismic array was deployed at the site shortly after the 2012 failure. The measured seismic response exhibited strong directional amplification (factors up to 35 at 3.5 Hz), higher than previously recorded on rock slopes. The dominant direction of ground motion was found to be parallel to the primary direction of deformation and perpendicular to open fractures, reflecting subsurface structure of the slope. The site has been later equipped with two semi-permanent seismic stations to monitor changes of the seismic response due to internal damage that may precede subsequent failure. Although failure has not yet occurred, our data reveal significant variations in the seismic response. Resonant frequencies exhibit seasonal trends related (both directly and inversely) to temperature changes, and are sensitive to freezing periods (resonant frequencies increase with temperature and during freezing).