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GNGTS 2016 sessione 2.2

marked directivity properties as evidenced by polarization analysis results. The ellipticity
diagrams show a corresponding sharp drop to zero at the same frequencies of the HVSR peaks,
indicating a high degree of linearity in the particle motion, and the polar plots show directivity
of particle motion approximately orthogonal to the fractures. In general, the results obtained
by the polarization analysis show a polarization perpendicular to the main fractures that can
be interpreted as vibrational motion of individual blocks (Galea et al., 2014), where vibration
frequency is related to geometrical and mechanical properties of the dislodged rock blocks (Got
et al., 2010).
Conclusions. In the western part of Cala Rossa bay (Favignana, Italy), an ongoing lateral
spreading process threats the “Pirrere” quarries, an important heritage site. On February-May
2015, seismic noise measurements were carried out both on the stable plateau area and on the
unstable zone that pointed out a different seismic response in the two areas. In the unstable
area, several HVRS peaks were observed at frequencies higher than 5.0 Hz and these peaks are
characterized by marked directivity properties. The results by HVSR and polarization analyses
allowed to associate the obtained seismic response to the vibrational motion of dislodged rock
blocks.
Considering the obtained preliminary results, more-detailed studies will be carry out to
characterize the vibrational modes of single rock blocks, in the frame of designing protection
strategies to manage the landslide process in Cala Rossa bay.

Acknowledgements. The Authors are grateful to J. Burjánek for the use of the polarization codes. The Authors
wish to thank the local authorities for supporting the geological and geophysical surveys.
References
Abate B., Ferruzza G., Incandela A. and Renda P.; 1995: Tettonica trascorrente nelle Isole Egadi (Sicilia occidentale).
Studi Geologici Camerti, vol. spec. 1995/2, 9-14.
Abate B., Incandela A. and Renda P.; 1997: Carta geologica delle isole di Favignana e Levanzo (Arcipelago delle
Egadi), Scala 1:12.500. Dip. di Geologia e Geodesia, Università di Palermo.
Antonioli F., Kershaw S., Renda P., Rust D., Belluomini G., Cerasoli M., Radtke U. and Silenzi S.; 2006: Elevation
of the last interglacial highstand in Sicily (Italy): A benchmark of coastal tectonics. Quaternary International,
145-146, 3-18.
Bonnefoy-Claudet S., Cotton F. and Bard P.�.; 2006: The nature of noise wavefield and its applications for site effects
studies: a literature review. Earth-Sci. Rev., 79(3), 205-227.
Burjánek J., Gassner-Stamm G., Poggi V., Moore J.R. and Fäh D.; 2010: Ambient vibration analysis of an unstable
mountain slope. Geophys. J. Int., 180(2), 820-828.
Burjánek J., Moore J.R., �ugsi Molina F.X. and Fäh D.; 2012: Instrumental evidence of normal mode rock slope
vibration. Geophys. J. Int., 188(2), 559-569.
Catalano R., Di Stefano P., Sulli A. and Vitale F.P.; 1996: Paleogeography and structure of the central Mediterranean:
Sicily and its offshore area. Tectonophysics, 260, 291-323.
Del Gaudio V., Coccia S., Wasowski J., Gallipoli M.R. and Mucciarelli M.; 2008: Detection of directivity in seismic
site response from microtremor spectral analysis. Nat. Hazards Earth Syst. Sci., 8, 751-762.
Falconi L., Peloso A., Puglisi C., Screpanti A., Tati A. and Verrubbi V.; 2015: Rockfalls monitoring along eastern
coastal cliffs of the Favignana island (Egadi, Sicily): preliminary remarks. In Lollino G., Giordan D., Marunteanu
C., Christaras B., �oshinori I. and Margottini C., eds: Engineering Geology for Society and Territory, 8, 287-291.
DOI: 10.1007/978-3-319-09408-3_50
Galea P., D’Amico S. and Farrugia D.; 2014: Dynamic characteristics of an active coastal spreading area using
ambient noise measurements-Anchor Bay, Malta. Geophys. J. Int., 199, 1166-1175.
Gigli G., Frodella W., Mugnai F., Tapete D., Cigna F., Fanti R., Intrieri E. and Lombardi L.; 2012: Instability
mechanisms affecting cultural heritage sites in the Maltese Archipelago. Nat. Hazards Earth Syst. Sci., 12, 1883-
1903.
Got J.-L., Mourot P. and Grangeon J.; 2010: Pre-failure behaviour of an unstable limestone cliff from displacement
and seismic data. Nat. Hazards Earth Syst. Sci., 10, 819-829.
Goudie A.; 2004: Encyclopedia of Geomorphology. Routledge, London (UK), 1156 pp.
Iannucci R., D’Amico S., Farrugia D., Galea P., Martino S. and Paciello A.; 2015: Seismic measurements in unstable
sea cliff areas. Atti del 34° Convegno Nazionale Gruppo Nazionale di Geofisica della Terra Solida. Tema 3:
Geofisica Applicata. Trieste (TS), 17-19 November 2015, vol. 3, 56-63.

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