Qβ , Qc , Qi , Qs of the Gargano Promontory (Southern Italy)

We have provided the first estimate of scattering and intrinsic attenuation for the Gargano Promontory (Southern Italy) analyzing 190 local earthquakes with M L ranging from 1.0 to 2.8. To separate the intrinsic Qi and scattering Qs quality factors with the Wennerberg approach (1993), we have measured the direct S waves and coda quality factors (Qβ , Qc) in the same volume of crust. Qβ parameter is derived with the coda normalization method (Aki 1980) and Qc factor is derived with the coda envelope decay method (Sato 1977). We selected the coda envelope by performing an automatic picking procedure from Tstart= 1.5 TS up to 30 s after origin time (lapse time TL). All the obtained quality factors clearly increase with frequency. The Qc values correspond to those recently obtained for the area. The estimated Qi are comparable to the Qc at all frequencies and range between 100 and 1000. The Qs parameter shows higher values than Qi , except for 8 Hz, where the two estimates are closer. This implies a predominance of intrinsic attenuation over the scattering attenuation. Furthermore, the similarity between Qi and Qc allows us to interpret the high Qc anomaly previously found in the northern Gargano Promontory up to a depth of 24 km, as a volume of crust characterized by very low seismic dumping produced by conversion of seismic energy into heat. Moreover, most of the earthquake foci fall in high Qi areas, indicating lower level of anelastic dumping and a brittle behavior of rocks.