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In this study, we derived the first 3-D P-wave seismic attenuation images (QP) as well as new 3-D VP and VP/VS models for the crust in southeastern Sicily. We used a large data set of local seismic events occurring in the time span 1994-2013. The results of this tomographic study have important implications on the seismic behaviour of the region. Based on velocity and attenuation images, we identified distinct volumes characterized by different fluid content, which correlate well with seismicity distribution. Moreover, the obtained velocity and attenuation tomographies help us to provide a more complete picture of the crustal structure of the area. High VP, high QP and high VP/VS values have been obtained in the crustal basement, below a depth of 8 km, and may be interpreted as due to the presence of serpentinized peridotites. Accordingly, the new model for the degree of serpentinization, retrieved from VP values, shows that the basement has an average serpentinization value of 96 ± 3 vol.% at 8 km, decreasing to 44 ± 5 vol.% at about 18-20 km. Our joint interpretation of geophysical and petrophysical evidence suggests that the nature and composition of the Hyblean upper lithosphere may differ from accepted and longestablished geological models, which consider this lithospheric block a continuation of the Africa continental plate. [ABSTRACT FROM AUTHOR]

Seismic wave attenuation in southeastern Sicily was investigated by using a data set of about 180 local earthquakes recorded in the period 1994–2003. We first estimated the quality factor of S waves and clarified its frequency dependence by means of the coda-normalization method, applied in the frequency range 1.5–15 Hz. The average as function of frequency is given by . A detailed separation of scattering attenuation from intrinsic absorption was also attempted by applying the multiple lapse time window analysis (MLTWA), under the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Intrinsic absorption dominates over scattering in the attenuation process at high frequencies (above 3 Hz). Below 3 Hz scattering is the predominant attenuation effect in the region, at the scale length of these frequencies. However, some discrepancies have been observed between the theoretical model and the observations. This indicates that models with depth-dependent velocity structure and/or non isotropic scattering should be taken into account in order to remove ambiguities in the interpretation of the results. [ABSTRACT FROM AUTHOR]

We analyzed about 150 local earthquakes recorded in Southeastern Sicily from 1994 to 2001 and estimated coda-Q, intrinsic and scattering attenuation. We used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands, obtaining a Qc varying with frequency as generally observed in tectonically active areas. Lapse time dependence has been also studied for the area, with the coda waves analyzed at window lengths ranging from 15 to 50 s, provided the coda duration permitted it. We found that Q0 (Qc at 1 Hz) increases with lapse time and we interpreted this as due to increasing Qc with depth. Conversely, the frequency dependence coefficient n is mostly stationary at all the lapse time window lengths.Finally, using the independent estimates of Qc and the total Q (QT) previously obtained for the area by other authors from direct S-waves of the same data set, we separated the intrinsic (Qi-1) from the scattering (Qsc-1) attenuation factor. The results suggest that in Southeastern Sicily intrinsic dissipation plays a predominant role with respect to scattering phenomena. [Copyright &y& Elsevier]