GNGTS 2013 - Atti del 32° Convegno Nazionale

Fig. 3 shows the resulting Q s for sections 3, 4, 5. The earthquakes are indicated as circles whose size corresponds to the magnitude. On the generic nth section characterized by y coordinate equal to y n , the earthquakes corresponding to y in the range [(y n-1 +y n )/2, (y n +y n+1 )/2] are projected. A cluster of earthquakes can be detected in the rightmost area of sections 4 and 5, corresponding to the Kobarid sequences. In the same area, a large decrease of the value of Q s , and therefore a larger attenuation, can be detected, in good agreement with the results by Gentili and Franceschina, 2011. Another cluster of seismicity can be detected in section 5 on the left, with a depth between 3 and 15 km. This seismicity belongs to the Claut area, where several low moderate magnitude earthquakes happened in the past (Gentili and Bressan, 2008). To the right of the cluster, there is on the top a region characterized by high values of Q s (low attenuation) and on the bottom with low value of Q s (high attenuation). Gentile et al. (2000) detected in the same region on the top an area of low V p / V s respect to the surrounding (1.76) and high V p velocity (6.2). Considering their results, together with the high value of Q s obtained in this paper, we hypothesize that it can correspond to un-fractured dolomitic limestones path, inside a more fractured one. On the bottom, Gentile et al. (2000) detect an area of V p / V s in the range 1.84-1.89. This region is interpreted by Gentile et al. (2000) as an highly fractured zone that corresponds to the Tramonti-But Chiarsò fault. This is compatible with our low attenuation results, even if the Q s anomaly extends deeper than the V p / V s one and, unlike for the high V p / V s zone, does not reach the surface, but is interrupted by al low attenuation zone. Both Bressan et al. (1992) and Gentile et al. (2000) detected an high P waves velocity body in the central part of the area with depth between 4 and 8 km. This is coherent with the detected high values of Q s (1100-1500). The even higher values of Q s at 15-18 km depth is not well resolved by both this work and by Bressan et al. (1992) and Gentile et al. (2000) works. References Aki K. and Richards, P.G.; 1980: Quantitative Seismology, Theory and Methods . Vol. 1, W.H. Freeman and Company, San Francisco, CA. Anderson J.G. and Hough S.; 1984: A model for the shape of Fourier amplitude spectrum of acceleration at high frequencies . Bull. seism. Soc. Am., 74 , 1969-1994. Bianco F., Del Pezzo E., Malagnini L., Di Luccio F. and Akinci A.; 2005: Separation of depth-dependent intrinsic and scattering seismic attenuation in the northeastern sector of the Italian Peninsula . Geophys. J. Int., 161 , 130-142. Bressan G., Bragato P.L. and Venturini C.; 2003: Stress and strain tensors based on focal mechanisms in the seismotectonic framework of the Friuli-Venezia Giulia region (Northeastern Italy) . Bull. seism. Soc. Am., 93 , 1280-1297. Bressan G., De Franco R. and Gentile F.; 1992: Seismotectonic study of the Friuli (Italy) area based on tomographic inversion and geophysical data . Tectonophysics, 207 , 383-400. Bressan G., Gentile G.F., Tondi R., De Franco R. and Urban S.; 2012: Sequential Integrated Inversion of tomographic images and gravity data: an application to the Friuli area (north-eastern Italy) . Bollettino di Geofisica Teorica ed Applicata, 53 , 2, 191-212. Bressan G., Kravanja S. and Franceschina G.; 2007: Source parameters and stress release of seismic sequences occurred in the Friuli-Venezia Giulia region (Northeastern Italy) and in Western Slovenia . Physics of the Earth and Planetary Interiors, 160 , 192-214. Burrato P., Poli M.E., Vannoli P., Zanferrari A., Basili R. and Galadini F.; 2008: Sources of Mw 5+ earthquakes in Northeastern Italy and Western Slovenia: an updated view based on geological and seismological evidence . Tectonophysics, 453 , 157-176. Carroll D. L.; 2001: GAFORTRAN. Genetic algorithm approach for parameter estimation. Urbana. http://cuaerospace. com/carroll/ga.html Castellarin A., Vai G.B. and Cantelli L.; 2006: The Alpine evolution of the Southern Alps around the Giudicarie faults: a late Cretaceous to early Eocene transfer zone . Tectonophysics, 414 , 203-223. Castro R.R., Pacor F. and Petrungaro C.; 1997: Determination of S-wave energy release of earthquakes in the region of Friuli, Italy . Geophys. J. Int., 128 , 399-408. Castro R.R., Pacor F., Sala A. and Petrungaro C.; 1996: S-wave attenuation and site effects in the region of Friuli, Italy . J. Geophys. Res., 101 , 22355-22369. Chen T. and Clayton R. W.; 2012: Structure of central and southern Mexico from velocity and attenuation tomography . J. Geophys. Res., 117 , B09302, doi:10.1029/2012J2IB009233. Console R. and Rovelli A.; 1981: Attenuation parameters for Friuli region from strong-motion accelerogram spectra . Bull. seism. Soc. Am., 71 , 1981-1991. Cormier V.; 1982: The effect of attenuation on seismic body waves. Bull. seism. Soc. Am., 72 , 6, S169-S200. 74 GNGTS 2013 S essione 1.1