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GNGTS 2015 SESSIONE 3. 2

On the other side, the HVSRs at Cala Rossa Bay generally become lower than l in the
frequency range between l and 2 Hz. Such an anomaly respect to the Anchor Bay si te could be
related to the complex network of man-made tunnels and caves within the Lower Pleistocene
carbonate grainstones, which could have a disturbing role in seismic wave propagation, leading
to an amplification of the ground motion vertical component.
Finally, the complex behavior of the HVSRs in the higher frequency range (10-60 Hz)
can be related to the vibrational behavior of the dislodged rock blocks. The seismic response
observed in frequency from 10 to 60 Hz is in agreement with the results published by Got et al.
(2010) showing thait the highest seismic energy was concentrateci in specific frequency bands
depending on geometrica! and mechanical properties of the rock blocks. Polarization analyses
(Bmjanek et al., 2010, 2012; Galea et al., 2014) will be canied out in order to derive the main
modes of vibration fora better comprehension of the seismic response of the cliff slope as well
as of its stability in case of earthquake shaking.
Conclusions. Preliminary results of seismic noise measurements canied aut in the westem
part of Cala Rossa Bay (Favignana, Italy) show that a site stratigraphic response exists and is
characterized by a HVSR peak between 5 and 6 Hz followed by a dip of the HVSR curve. It
was also observed a HVSR dip below level l in a narmw frequency range, between l and 2 Hz,
that could be related to the dense network of man-made tunnels and caves within the Lower
Pleistocene carbonate grainstones of the Island.
A complex local seismic response was also observed at higher frequencies (10-60 Hz) that
can be related to the seismic response of the dislodged rock blocks. The results obtained at
Cala Rossa Bay were compared to the ones obtained at Anchor Bay in Malta due to the high
similarity of the local geologica! and lithotechnical setting responsible for ongoing latera!
spreading landslide processes.
More-detailed studies will be cany out by experiencing analytical approaches devoted to
characterize the vibrationalmodes of the surveyed rock blocks, in order to evaluate the sea cliff
stability conditions during earthquake shaking.
Acknowledgements. This study is part of a PhD research (Roberto Iannucci) at the Department of Earth Sciences
of Sapienza University of Rome. TheAuthors wish t o thank Luca Falconi, V!adimiro Verrubbi an d Augusto Screpanti
for data and information provided about the Cala Rossa Bay area and Fabio Martorelli for bis useful support in the
field geologica! survey.
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