GNGTS 2013 - Atti del 32° Convegno Nazionale

References Andrews D.J.; 1986: Objective determination of source parameters and similarity of earthquakes of different size , in Earthquake Source Mechanics, S. Das, J. Boatwright, and C.H. Scholz, Editors, A.G.U. monograph 37, 259-267. Brune J.; 1970: Tectonic stress and spectra of seismic shear waves from earthquakes. J. Geophys. Res., 75, No. 26, 4997- 5009. Brune J.; 1971: Correction. J. Geophys. Res., 76, No. 20, 5002. Castro R.R., Pacor F., Puglia R., Ameri G., Letort J., Massa M., Luzi L.; 2013: The 2012 May 20 and 29, Emilia earthquakes (Northern Italy) and the mail aftershocks: S-wave attenuation, accelerationsource functions and site effects. Geophys. J. Int. doi: 10.1093/gji/ggt245. Console R., Rovelli A.; 1981: Attenuation parameters for Friuli region from strong-motion accelerogram spectra. Bull. Seism. Soc. Am., 71, No. 6, 1981-1991. Gallo A., Costa G., Suhadolc P.; 2013: Near real-time moment magnitude estimation. Submitted to Bull. Earth. Eng. Gorini A., Nicoletti M., Marsan P., Bianconi R., De Nardis R., Filippi L., Marcucci S., Palma F., Zambonelli E.; 2010: The Italian strong motion network . Bull Earthquake Eng. doi: 10.1007/s10518-009-9141-6. Hanks C.; 1977: Earthquakes stress drops, ambient tectonic stresses and stresses that drive plate motions. Pure Appl Geophys., 115, 441-458. Hanks C., Kanamori H.; 1979: A moment magnitude scale. J. Geophys. Res., 84, 2348-2350. Kanamori, H.; 1994: Mechanics of earthquakes . Ann. Rev. Earth Planet. Sci. 22, 207-237. Madariaga R.; 1976: Dynamics of an expanding circular fault. Bull. Soc. Am.,66, No.3, 639-666. Malagnini L., Hermann R.B., Munafò I., Buttinelli M., Anselmi M., Akinci A., Boschi E.; 2012: The 2012 Ferrara seismic sequence: Regional crustal structure, earthquake sources, and seismic hazard. Geophys. Res. Lett., 39, L19302, doi:10.1029/2012GL053214, 2012. Ottemoller L., Havskov J.; 2003: Moment magnitude determination for local and regional earthquakes based on source spectra. Bull. Seism. Soc. Am., 93, No. 1, 203-214. Pondrelli S., Salimbeni S., Perfetti P., Danecek P.; 2012: Quick regional moment tensor solutions for the Emilia 2012 (northern Italy) seismic sequence. Annals of Geophysics, 55, 4, doi: 10.4401/ag-6146. Richter C.F.; 1935: An instrumental earthquake magnitude scale . Bull. Seism. Soc. Am., 25, 1-32. Saraò A., Peruzza L.; 2012: Fault-plane solutions from moment-tensor inversion and preliminary Coulomb stress analysis for the Emilia Plain. Annals of Geophysics, 55, 4, doi: 10.4401/ag-6134. Scognamiglio L., Margheriti L., Mariano Mele F., Tinti E., Bono A., De Gori P., Lauciani V., Lucente F.P., Mandiello A.G., Marcocci C., Mazza S., Pintore S., Quintiliani M.; 2012: The 2012 Pianura Padana Emiliana seismic sequence: locations, moment tensors and magnitudes. Annals of Geophysics, 55, 4, doi: 10.4401/ag-6159. Zambonelli E., De Nardis R., Filippi L., Nicoletti M., Dolce M.; 2011: Performance of the Italian strong motion network during the 2099, L’Aquila seismic sequence (central Italy). Bull. Earth. Engin., 2011, 9, No. 1, 39-65. Underground array recordings of local and regional earthquakes in Central Italy: a tool for testing equipartition of energy in a diffusive wavefield D. Galluzzo 1 , M. La Rocca 1 , L. Margerin 2 , E. Del Pezzo 1 , R. Scarpa 3 1 Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano, Napoli, Italy 2 Université de Tolouse, Tolouse, France 3 Università degli Studi di Salerno, Salerno, Italy Introduction. The scattering of seismic waves propagating in heterogeneous media is more complex than the scattering of other waves (electromagnetic, acoustic) due to the conversion from P to S and vice versa. The multiple scattering theory describes sufficiently well the energy decay along the earthquake coda. When the travel time is much greater than the mean free scattering time and the travel distance is much greater than the mean free scattering distance, the seismic wavefield is expected to be diffuse, as observed for electromagnetic and acoustic waves propagating through heterogeneous media. When a high number of waves of similar amplitude reach the observation point at the same time with different propagation directions and random phase, the resulting wavefield is said diffusive. The most relevant features of such wavefield are a small variation of amplitude with time and a low coherence. Regarding seismic waves, a wavefield is diffusive at a given frequency if in any chosen time window there are many P and S waves (and surface waves if the observation point is at or near the free surface) of comparable amplitude propagating with different random directions and random 62 GNGTS 2013 S essione 1.1