GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Exploring Italy's Present-Day Stress Field Complexity through Utlisaton of Geophysical, Geological, and In Situ Drilling Data P. Montone and M. T. Mariucci Isttuto Nazionale di Geofsica e Vulcanologia, Roma, Italy Comprehensive understanding of the shallow crust's present-day stress feld in Italy is crucial for enhanced crustal modelling and a more insight into tectonic processes and fault slip behaviour. Adhering to the guidelines of the World Stress Map, this study presents the latest fndings on horizontal stress orientatons and stress regime in Italy. The analysis is based on recent in situ drilling data and focal mechanisms of signifcant earthquakes (Figure 1). New borehole breakout analysis was conducted on 14 deep wells along the Adriatc coast and ofshore, revealing horizontal stress orientatons in nine wellbores. Stress orientatons and tectonic regimes were deduced from the analysis of 21 earthquake focal mechanisms with magnitudes equal to or greater than 4, occurring between January 1, 2022, and October 31, 2023. The updated fndings from 10 wells in the mid-southern Adriatc Sea, where no borehole ovalizaton was observed, highlight the absence of breakout zones along these wells. These new data will be incorporated into the Italian Present-day Stress Indicators (IPSI) database, scheduled for release at the beginning of the year. The IPSI database, managed at INGV (Isttuto Nazionale di Geofsica e Vulcanologia), serves as a georeferenced repository containing informaton on the present-day stress feld of the crust. The database includes horizontal stress orientatons accurately analysed and standardised for global reliability and comparability, with 969 entries (all qualites) updated to October 2023. IPSI database consolidates informaton on contemporary stress within the Earth's crust's upper 40 km, derived from various stress indicators categorised into fve main groups. In the specifc context of the Mw 5.5 2022-2023 Adriatc seismic sequence, newly acquired breakout data from deep boreholes exhibit coherent Shmin orientatons ranging from N126 to N132, characterised by small standard deviatons, indicatng their high quality. These results, extending from the surface to approximately 4000 m, fll an informaton-defcient depth range, because the entre seismic sequence is positoned between 5 and 10 km depth. The seismic sequence, comprising six events with M≥4, yielded four available TDMT focal mechanisms, with three displaying pure thrust faultng and one a strike-slip mechanism. The consistently oriented minimum horizontal stress, evident in the N133 orientaton for the Mw=5.5 event at 5 km depth, aligns with the northern Apennines' axis, confrming stress trends inferred from existng datasets in inland and southern sectors. The intricate plate motons and the presence of multple subducton zones have given rise to simultaneous and geographically proximate diverse stress regimes.