GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Anatomy of clustering from parametric space- tme analysis of seismicity. G. Rossi 1 , G. Bressan 2 , C. Barnaba 1 , A. Peresan 1 1 Natonal Insttute of Oceanography and Applied Geophysics –OGS, Italy 2 formerly Natonal Insttute of Oceanography and Applied Geophysics –OGS, Italy We propose a multparametric approach to quanttatvely describe the temporal and spatal evoluton of seismicity in regions, where the spatal and temporal patern of seismicity shows no obvious trends and cannot be resolved on well-defned fault planes (Bressan et al., 2021). We consider fve diferent parameters. The spato-temporal evoluton of Shannon entropy quantfes the degree of organizaton or disorder in the energy distributon of an earthquake populaton (Telesca et al., 2004). The temporal changes in the classical estmates of the b-value from the Gutenberg-Richter (GR) law (Gutenberg and Richter, 1944) capture the balance between small and large-magnitude events. The temporal variaton of the fractal dimension of hypocenters refects the evoluton of the spatal seismicity patern. The “nearest neighbour" distance (Baiesi and Paczuski, 2004; Zaliapin and Ben-Zion, 2013) further enables characterizing the clustering propertes of seismicity (Varini et al., 2021). Finally, the evoluton of seismicity can be further investgated with multdimensional principal component analysis (PCA) (Rossi and Ebblin, 1990; Bressan et al. 2018a; 2021). Time adds to the spatal coordinates in the constructon of the 4D- correlaton matrix, which can be interpreted as a hyper-ellipsoid. The hyper-ellipsoid spatal axes projecton onto a 3D space depicts the best-ft plane orientaton and the extent of the volume interested by the afershocks. The fourth axis projecton onto space indicates the shock propagaton directon and can be used to infer the relatonships between the various planes that actvate in tme (Bressan et al., 2021). We have focused on an area in northeastern Italy where the maximum interference between the NW-SE oriented Dinaric transpressive structures and the E-W oriented Alpine thrusts occurs, bound to the superpositon of three main tectonic phases that afected the area through tme (Ponton, 2010). The inversion of the focal mechanisms indicates a dominance of reverse mechanisms but the presence of strike-slip solutons is also relevant (Saraò et al., 2021). Comparison between the stress and strain tensors reveals planes of mechanical weakness that are oriented diferently, ofen unfavourably with respect to the principal stress axes, suggestng heterogeneous crustal strength (Bressan et al., 2018b). This area is characterized by a relatvely high seismic hazard and has experienced several destructve earthquakes in the past. The most severe ones occurred in 1700 (I0=VIII-IX MCS on the Mercalli-Cancani-Sieberg scale, Mw=5.7), 1788 (I0=IX, Mw=5.2), 1928 (I0=IX, Mw=6.0), 1959 (I0=VII-VIII, Mw=5.2) (Rovida et al., 2016; Bressan et al., 2019). For our analysis, we considered a dataset of 1493 earthquakes that occurred between 2015 and March 2020 and whose magnitude M D is between 0.4 and 4.0. The earthquakes were located