## 4 Discussion  
The quality factor \(Q_{c}\) has been estimated in order to assess the effect of tectonic and seismic activity in the hazardous region of the GP. Before drawing conclusions about the GP tectonics, the meaning of what \(Q_{c}\) physically measures should be re-addressed. Within the frame of the single-scattering theory, \(Q_{c}\) is considered representative of the total attenuation. The total attenuation of seismic waves is the sum of intrinsic \(Q_{i}\) and scattering \(Q_{s}\) attenuation: the first term accounts for the conversion of seismic energy into heat through anelastic absorption; the second term accounts for seismic energy redistribution through refraction, reflection and diffraction at random discontinuities distributed inside a homogeneous medium. The severe trade-off between the estimates of the intrinsic \(Q_{i}\) and the scattering \(Q_{s}\) is due to the mathematical formulation of the model itself [1] and it is impossible to deduce from the \(Q_{c}\) estimates which quality factor (\(Q_{i}\) or \(Q_{s}\)) prevails. Many studies indicate that, in a fairly homogeneous crust, \(Q_{i}\) would prevail over \(Q_{s}\) in the \(Q_{c}\) value ([39, 61, 62] among others). This could be true on a regional scale; where an average Earth crust is sampled, heterogeneities appear as smoothed and the \(Q_{c}\) distribution can be considered representative of the anelastic absorption. If \(Q_{c}\) is analyzed with respect to frequency, it appears that at frequencies \(f_{c}\) < 6 Hz, scattering is dominant, whereas, at frequencies \(f_{c}\) > 6 Hz, intrinsic attenuation is dominant [9, 63]. Monte Carlo simulations based on the law of energy conservation showed that for short lapse times, the single-scattering model is applicable, while for long lapse times, the diffusion model is more appropriate [64]. In particular, at long lapse times, when coda waves are in the diffusive regime, \(Q_{c}\) asymptotically approaches the intrinsic \(Q_{i}\) in a uniform half-space model [12]. By using different methods, the separation of \(Q_{i}\) and \(Q_{s}\) from \(Q_{c}\) has been estimated both in Italy and worldwide, in many tectonic contexts: the Adaman Sea [65]; the Alborz region (Iran) [66]; the Almeria Basin, Southwestern Iberian Peninsula (for \(f_{c}\) > 3 Hz) [47];  
Figure 8: Section maps of \(Q_{c}\) and \(\sigma\) at various depths for \(t_{L}\) = 30 s: (**a**) \(f_{c}\) = 3 Hz; (**b**) \(f_{c}\) = 6 Hz; (**c**) \(f_{c}\) = 12 Hz. The coastline is in white. Labels A, B, C, D and E refer to the \(Q_{c}\) anomalies commented in the discussion section. Spain and Turkey [67]; the Tokai region (Japan) [1]; Northeastern Italy [61]; the Messina Strait (Southern Italy) [45]. The results of all these studies suggest that the attenuation of coda waves is dominated by intrinsic attenuation. The same result was achieved for the Southern Apennines (Italy) [62], in a regional-scale study that included the GP. In this work, with respect to a previous analysis [23], we used an improved dataset of microearthquakes that was one order of magnitude greater, recorded by both the OT and IV network stations, extending the seismic coverage of the area. The differences between the results of this study and those obtained in the previous one [23] are due to the different magnitude ranges considered. In fact, by increasing the event magnitude, the signal-to-noise ratio also increased, giving rise to more reliable results. Moreover, since the network geometry used for this study was larger than the previous one, the \(Q_{c}\) values were averaged at different distances. Several observations from different regions worldwide [40] indicate an increase of the value of \(Q_{c}\) when increasing the lapse time window \(t_{L}\), due to the greater penetration of waves in the deeper Earth, where the seismic attenuation is less pronounced. Therefore, seven \(t_{L}\) windows were taken, from 10 to 40 s, with a 5-s time step, to estimate the attenuation at different lapse times, i.e., at different depths.