GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.3 GNGTS 2024 Difusivity analysis of clustered seismicity in Central-Southern Apennines G.M. Cipressi 1 , A. Vuan 4,5 , M.A. Romano 4 , G. Lavecchia 2,3 , R. de Nardis 2,3 1 Department of Engineering and Geology, University “G. d’ Annunzio” of Chiet-Pescara, Italy 2 DiSPuTer - University of Chiet-Pescara 'G. d'Annunzio', Italy 3 CRUST- Interuniversity Center for 3D Seismotectonics with Territorial Applicatons, Italy 4 Natonal Insttute of Oceanography and Applied Geophysics (OGS), Italy 5 Natonal Insttute of Geophysics and Volcanology (INGV), Italy Seismic swarms are defned as a set of clustered earthquakes with high spato-temporal variability and with the absence of a main shock. They can originate in diferent tectonic contexts related to the migraton of deep fuids that can alter the stress feld (Roland et al., 2009). In partcular, the difusivity parameter, defned by Shapiro et al. (1997) and linked to the migraton of the hypocenters over tme, allows us to associate the swarms' temporal duraton with the rocks' permeability characteristcs. Swarms characterized by long duratons (years) and low difusivity values (10 -3 -10 -2 m 2 /sec) are associated with low permeability fault systems. On the contrary, shorter duratons (days) and high difusivity values (0.5-1 m 2 /sec or greater) indicate the presence of highly permeable systems in which seismicity is induced by the rise of fuids at high pressures (Amezawa et al., 2021). We focus on the clustered seismicity in the central-southern Apennines, which extends from the south of L'Aquila to Benevento, to analyze the spato-temporal characteristcs of the swarms and the relatonship between their temporal duraton and difusivity. Compared to the rest of the chain, this sector is characterized by (1) low seismicity rates, which do not allow us to follow the evoluton of seismicity and the mechanisms underlying it, and (2) a high seismic risk, as demonstrated by the strongest and most destructve sequences recorded within the historical catalogs which magnitude M ~ 7. We analyzed the seismicity reported in the catalog of absolute locatons CLASS (Latorre et al., 2022), which describes Italian seismic actvity over the past 37 years (1981-2018). Additonally, we augmented the catalog within a 7-year tme window (2012-2018) using a template matching technique (Vuan et al., 2018). This choice was made based on the optmal distributon and operaton of the seismic network. The inital catalog is improved, lowering the completeness magnitude by more than one degree (+ 20,000 events with -1.5<M<5.0). This approach allowed the analysis and comparison of clustered seismicity in two catalogs with diferent tme extensions and resolutons. Clustered seismicity is defned relatve to the background using a nearest-neighbor technique (Zaliapin & Ben-Zion, 2020). Due to the great spato-temporal variability of the seismic