GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 The 1981-2018 Italian catalog of absolute earthquake locations (CLASS) D. Latorre, R. Di Stefano, B. Castello, M. Michele, L. Chiaraluce Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy Introduction CLASS (acronym for “Catalogo delle Localizzazioni ASSolute”), is a catalog of earthquake locations computed in a 3D velocity model of the Italian region with a probabilistic approach and a non-linear inversion algorithm (Latorre et al., 2022). CLASS (available at https://doi.org/10.13127/class.1.0 ) is currently the most complete and homogeneous hypocenter location catalog of earthquakes recorded in Italy from 1981 to 2018. Previous catalogs of the Italian instrumental seismicity are 1) the CSTI (Catalogo Strumentale dei Terremoti Italiani, CSTI working group, 2001, 2005), that provides standardized information of P and S phase arrival times, hypocenter locations, and magnitudes by merging seismic data collected from 1981 to 1996 by several permanent seismic networks, and 2) an extension of the CSTI catalog for the period 1997-2002 proposed by Chiarabba et al. (2005), whose events were used by Castello et al. (2006) in the CSI1.1 catalog (Catalogo della Sismicità Italiana, hereafter CSI) updating the magnitude estimates of the relocated events from Chiarabba et al. (2005). A last study (Chiarabba et al., 2015) extends the computation of earthquake hypocenter locations up to 2012 by including seismic phases arrival times of the Italian Seismic Bulletin. All the hypocenter solutions presented in these catalogs were obtained by using both a simplified 1D velocity models of the Italian region and a linearized hypocenter location method, leading to varying levels of earthquake mislocation due to the effects of lateral heterogeneities that characterize the Italian velocity structure. On the contrary, the seismicity of the CLASS catalog was relocated in a 3D velocity model of Italy obtained with a tomographic inversion by Di Stefano and Ciaccio (2014). We use the probabilistic, nonlinear earthquake location algorithm NonLinLoc (hereafter NLL, Lomax et al., 2000, 2014) that gives a complete estimation of the hypocenter location uncertainties, whose parameters are included in a quality analysis proposed by Michele et al. (2019). This procedure provides a homogeneous, consistent catalog characterized by accurate 3D earthquake locations, robust evaluations of location uncertainties, and a quantitative “user friendly” classification of the results.