GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Crustal structure of the volume involved in the 2010-2014 sequence Fig 1. The map shows the Pollino area. The red circles represent the epicenters of the 870 earthquakes used for seismic tomography in Napolitano et al. (2021a). The blue triangles, cyan circles and green diamonds represent the stations of the different seismic networks operated by the National Institute of Geophysics and Volcanology (INGV), University of Calabria (UNICAL) and Deutsche GeoForschungsZentrum (GFZ) in Potsdam (Germany), respectively. The inset in the upper right corner shows the study area localized with respect to the Italian peninsula. A seismic tomography of the Pollino area was performed using 870 earthquakes (Fig. 1, M L > 1.7) recorded at permanent and temporary stations installed in the area during the intense 2010-2014 seismic sequence (Napolitano et al., 2021a). 3D models of P-wave velocities (V P ), S-waves (V S ) and V P /V S ratios of the first 10 km depth and accurate re-locations of earthquake hypocenters in the new 3D model were obtained. Interpretation of the tomographic images indicates that the ductile Apennine platform (V P 5.3 km/s) overlies the more brittle Apulian carbonate platform (V P 6.0 km/s) at about 5 km depth. Geophysical investigations in the close Val D'Agri (Improta et al., 2017) and Irpinia (Improta et al., 2010) regions support the association of these velocity structures to similar tectonic units. The central sector of the seismogenic volume shows a clear thrust and fold interface, typical of many Apennine areas. Along this structure, belonging to the western lobe of the sequence, most of the seismicity occurred, including the strongest event (M L 5.0). High V P (>6.8 km/s) and high V P /V S (>1.9) anomalies intersect the southern margin of this structure. These values have been interpreted as fluid-saturated rocks, in agreement with what has been found in similar geological contexts in the Apennines (Amoroso et al., 2014; Chiarabba et al., 2020) and corroborated in recent work by De Gori et al. (2022). This high V P and high V P /V S volume seems to originate deeper, south-east of the western seismicity lobe, finding excellent agreement with the presence of a high total attenuation volume, located at an average depth of 12.5 km (Sketsiou et al., 2021). The same area was also identified as an area of high scattering and high absorption in a 2D tomographic model, using the peak-delay and coda-wave attenuation technique over a broad frequency band, respectively (Napolitano et al., 2020). The peak delay is the time interval between the arrival of the S-wave and the maximum amplitude of the waveform envelope (Takahashi et al.,