GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Fig 3. Comparison at 5 km depth between absorption maps (at 3 and 6 Hz, in the top and middle panels respectively) and pore pressure excess map, modified after De Matteis et al (2021). The green rectangle in the absorption maps represents the area of the bottom panel. Kinematic parameters and tomography of focal mechanisms An important result derived from seismic tomography (Napolitano et al., 2021a) is the re-location of the M L > 1.7 magnitude events, which allowed us to obtain details about the orientation and size of the fault that generated the M L 5.0 magnitude event and only partially of the M L 4.3 event. This result is also relevant from a geological point of view. In fact, the images clarify that the source of the mainshock is at a weakness point at the interface between the Apennine platform and the underlying Apulian platform, while the fault responsible for M L 4.3 event is totally immersed within the Apennine platform. Seismicity along the western cluster was also characterized by the occurrence of clusters of micro-earthquakes (0.6 < M L < 1.2) of similar wave shape, located by Napolitano et al. (2021b) using the master-slave relative location technique (Got et al., 1994). Such small-magnitude events are superimposed on the stronger ones used in tomography, providing greater detail on the structure responsible for the mainshock and a temporal directionality of the micro-seismicity. The earthquakes align along part of the structures proposed in recent geological work in the area (Brozzetti et al. 2017; Cirillo et al., 2022) and draw a 10 km x 4 km seismogenic fault, oriented NW-SE and dipping to the SO at an angle of 40°-45°. Clusters of similar events occur mainly in areas characterized by the presence of fluids, and in fact the M L 5.0 event area is characterized by high V P and high V P /V S , interpreted as indicative of the presence of fluids, similar to other Apennine regions (Amoroso et al., 2014; Chiarabba et al., 2020). An excess of pore pressure was also highlighted by De Matteis et al. (2021) who provided the first