S-waves attenuation and separation of scattering and intrinsic absorption of seismic energy in southeastern Sicily (Italy)

Seismic wave attenuation in southeastern Sicily was investigated by using a data set of about 180 local earthquakes (1.5 ≤M
L
≤ 4.6) recorded in the period 1994–2003. We first estimated the quality factor of S waves (Q
S
) and clarified its frequency dependence by means of the coda-normalization method, applied in the frequency range 1.5–15 Hz. The average Q
S
as function of frequency is given by Q
S
= 49f
^0.88
.A detailed separation of scattering attenuation (Q
⁻¹
s
) from intrinsic absorption (Q
⁻¹
i
) 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.