GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 3D Hypocenters relocaton in high-resoluton central Mediterranean velocity model I. Menichelli 1* , P. De Gori 1 , C. Chiarabba 1 1 Isttuto Nazionale di Geofsica e Vulcanologia (Rome, Italy) In this study, a new 3D relocated hypocenters catalogue has been built for the Italian region using an updated 3D velocity model computed for the central Mediterranean area (Menichelli et al., 2023). Classical one-dimensional velocity models, due to their limitaton in recovering lateral heterogeneous variatons in the velocity structure, ofer only a simplifed depicton of the reality. For this reason, the necessity to use 3-D velocity models in the locaton of hypocenters, which consider the inhomogeneous structure of the diferent layers that consttute the earth's interior, has been emerging in recent years. The 3D tomographic model used has been computed invertng P- and S- arrival tmes recorded between 2014-2021 by the RSN (Italian Seismic Network) and AlpArray (AlpArray 2015; Hetenyi et al., 2018) seismic network. In partcular, the seismic data set includes Pg, Pn, Sg, and Sn, and the related arrival tmes were manually picked within a maximum epicentral distance of 1000 km. We used the code Simulps 14 (Thurber 1983, 1999) to locate seismic events with the 3D velocity model. The method uses P and S–P arrival tmes to solve for hypocentral parameters while keeping fxed the Vp and Vs velocity structure. We compute the hypocentral parameters for about 170.000 seismic events recorded by the INGV seismic network (RSD) that occurred in the period 2005–2023 startng from 1D absolute locatons obtained using the best ft 1D Minimum Velocity Models and procedure presented in Menichelli et al., (2022). The decision to start with an already precise localizaton was made with the intenton of improving the accuracy of localizaton as much as possible. In order to determine stable solutons we selected only seismic events with at least 3 P-wave and 2 S-wave arrival tmes, the closest staton within 50 km and rms ≤ 0.4 s. A further selecton was also performed on the basis of the focal depth extracted from the previous 1D hypocentral locatons: seismic events occurring at signifcant depths (≥ 80 km) were localized using a local model built ad hoc for the southern Tyrrhenian area using the arrival tmes of intraslab seismicity (Chiarabba et al., 2008). The decision was aimed at achieving accurate localizaton even at mantle depths. The preliminary results obtained by the statstcal analysis show low errors for the hypocentral coordinates (maximum peak at around 7 km for x and y-coordinates and at around 1-2 km for the z-coordinate) and small rms values (< 0.5 s).