GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 of relative location indicates a much smaller volume than that obtained from absolute location. Nevertheless, the extent of the distribution of the hypocenters is significantly larger than the length of the rupture estimated from the magnitude of the strongest event of the swarm. ​ Conclusions Detailed analysis of seismic swarms is very important in areas where strong earthquakes have not occurred for many decades. In fact, seismic swarms may allow the identification of active faults whose existence and seismogenetic potential are unknown. Therefore, the study of seismic swarms is very useful to identify active seismogenetic sources, especially when they do not have a correspondence with known tectonic structures. This is especially true for swarms occurring at depth greater than 10 km and/or with epicenter in the sea, for which it is often impossible to associate them with faults whose traces can be seen on the surface. It is worth to note that in Calabria the reference seismic hazard in coastal areas may be underestimated because of the lack of strong earthquakes occurred in the last century. The relative location of many tens of hypocenters allows to identify the geometry of the source and to estimate its volume. In cases where the distribution of hypocenters is characterized by a very anisotropic shape, it is also possible to estimate direction and inclination of the portion of the fault that generated the swarm. The distribution of the hypocenters in a seismogenetic volume much greater than the extent of the mainshock rupture suggests that many events occur on different sectors of the same fault. These sectors may not overlap themselves or may not be contiguous. Conversely, this feature can also suggest that many events occur on different faults distributed in a highly fractured crustal volume. Finally, the kinematics of the events gives very important information about the active stress field in the volume surrounding the source. Figure 3. Focal mechanisms of (a) 7 Mesima valley swarm earthquakes and (b) 4 Bagnara Calabra swarm earthquakes.