GNGTS 2018 - 37° Convegno Nazionale

272 GNGTS 2018 S essione 1.3 important role in determining attenuation of seismic waves in both areas. At higher frequency, intrinsic attenuation prevails over scattering. The average Q i , Q s and Q T show a strong frequency dependence, with the coefficient n ranging from ca. 0.7 to 1.9. The frequency dependence of Q s is stronger than that of Q i in both regions and, according to various seismologists, it can be also considered as an indirect indicator of macroscale Earth heterogeneity (Leary, 1995), being it observed when the heterogeneities responsible for scattering are of sizes comparable to the lowest frequency analysed (e.g. Mayeda et al. , 1992; Canas et al. , 1998; Tuvè et al. , 2006; Giampiccolo et al. , 2006;  Mukhopadhyaya et al. , 2010). Similar results have been obtained in other volcanoes, such as Mt. Merapi (Wegler and Lur, 2001) and Mt. Vesuvius (Bianco et al. , 1999; Del Pezzo et al. , 2016). Our findings match well with the data obtained by means of seismic tomography and confirm that both Mt. Etna and Aeolian Islands are characterized by pronounced heterogeneity, i.e. strong velocity contrasts which are able to produce high scattering of shear waves. References Bianco, F., Castellano, M., Del Pezzo, E. and Ibanez, J.M.; 1999: Attenuation of short period seismic waves at Mt. Vesuvius, Italy . Geophys J. Int. 138 (1): 67–76. Canas, J.A., Ugalde, A., Pujades, L.G., Carracedo, J.C., Blonco, M.J. and Soler, V.; 1998: Intrinsic and scattering seismic wave attenuation in the Canary Islands. J. Geophys. Res. 103, 15037–15049. Del Pezzo, E., Bianco F., Giampiccolo E., Tusa G. and Tuvè, T.; 2015: A reappraisal of seismic Q evaluated at Mt. Etna volcano. Receipt for the application to risk analysis . J. Seism. 19 (1), 105–119. Del Pezzo, E., Ibanez, J., Prudencio, J., Bianco, F. and De Siena, L.; 2016: Absorption and Scattering 2D Volcano Images from Numerically Calculated Space-weighting functions . Geophys. J. Int. 206: 742-756. doi: 10.1093/gji/ ggw171. Giampiccolo, E., Tuvè, T., Gresta, S. and Patanè, D.; 2006: S-waves attenuation and separation of scattering and intrinsic absorption of seismic energy in southeastern Sicily (Italy). Geophys. J. Int. 165 (1), 211–222. Leary, P.C.; 1995: The cause of frequency-dependent seismic absorption in crustal rock , Geophys. J. Int. doi: https:// doi.org/10.1111/j.1365-246X.1995.tb03542.x Mayeda, K., Koyanagi, S., Hoshiba, M., Aki, K. and Zeng, Y.; 1992: A comparative study of scattering, intrinsic, and coda Q−1 for Hawaii, Long Valley and central California between 1.5 and 15 Hz. J. Geophys. Res. 97, 6643–6659. Mukhopadhyay, S. and Sharma, J.; 2010: Attenuation characteristics of Garwhal–Kumaun Himalayas from analysis of coda of local earthquakes. J. Seism. 14, 693–713 .http://dx.doi.org/10.1007/s10950-010-9192-9. Tuvè, T., Bianco, F., Ibañez, J.M., Patanè, D., Del Pezzo, E. and Bottari, A.; 2006: Attenuation study in the Straits of Messina area (Southern Italy). Tectonophysics 421: 173-185. Wegler, U. and Luhr, B.G.; 2001: Scattering behaviour at Merapi volcano (Java) revealed from an active seismic experiment. Geophys. J. Int. 145:579–592. Fig. 2 - Pattern of Qi-1, Qs-1 and Qt-1 vs. frequency for each study area.