GNGTS 2022 - Atti del 40° Convegno Nazionale

24 GNGTS 2022 Sessione 1.1 segmentation (Chiarabba et al. , 2020; Akinci et al. , 2020), that led to both scattering and trapped waves, as also evinced by high-scattering anomalies focusing in the south and west zones (Gabrielli et al. , 2021). An increase of seismic attenuation is expected due to the large number of different tectonic features, which reflects in lower quality factor Q, which is typical of near-surface rocks. Moreover, according to Pastori et al. (2019), the area between Amatrice and Accumuli regions, can be considered as a heavily fractured zone in which fluids are preferentially channeled. On the other side, the eastern part of the Apennine chain is characterized by tectonic stability and less attenuation (Castro et al. , 1996; Malagnini et al. , 2002). Figure 3a shows the distribution of the near-site attenuation parameter for reference rock stations identified according to Lanzano et al. (2020) using several proxies of the site response. We can observe that three sites in the north (APEC, ATPI, and CAFI) have high values of κ 0 that are close to the edge of basins where some sedimentation may be present. Figure 3b displays the distribution of non-reference sites and the values of κ 0 obtained for those stations. These outcomes with low values of κ 0 does not necessarily correlate with the V s ,30 of a given station, since κ 0 may include the effect of attenuation beyond the first 30 m from the surface, which are usually obtained using invasive methods that may alter the elastic properties of the rocks. Conclusions and future perspectives. Our results shown that most of the high-frequency attenuation takes place near the site, because κ avg ( r ) contributes with only 20% of the spectral decay. The spatial variability of κ avg ( r ) suggest an anisotropic behavior of the high-frequency attenuation, probably related to different local geology, faulting activity and tectonic structures in the different directions with respect to the Apennine orientation (Castro et al. , 2022a). Moreover, we find that the higher values of κ avg ( r ) in the southern regions of Central Italy a) b) Fig. 3 - Spatial distribution of the near-site attenuation parameter κ 0 obtained for reference stations a) and non-reference stations. The stars are the location of earthquakes with magnitudes greater than 5 plotted for reference.