GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 What we can say (or not) about the seismic sequence of the November 9 th 2022, Mw 5.5, earthquake in the Marche offshore: an analysis of the Italian Seismic Bulletin on phase interpretation, velocity models and uncertainties of earthquake locations D. Latorre e Gruppo di lavoro Bollettino Sismico Italiano - L. Arcoraci, A. Battelli, P. Battelli, M. Berardi, B. Cantucci, C. Castellano, B. Castello, D. Cheloni, M.G. Ciaccio, R. Di Stefano, L. Improta, A. Lisi, A. Marchetti, L. Margheriti, M. Michele, C. Montuori, A. Nardi, N. M. Pagliuca, L. Pizzino, T. Sgroi Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy Introduction In November 2022 a seismic sequence occurred in the Marche offshore, about 29 km from the coast and the city of Fano. The sequence started on November 9 (06:07:25 UTC) with a M L =5.7 earthquake (Mw=5.5 from TDMD computation, Scognamiglio et al., 2006), immediately followed by a M L =5.2 earthquake (06:08:29 UTC) located about 8 km to the south. The two mainshocks activated a seismic sequence with about 400 aftershocks lasting the first week, 13 of them with M L >= 3.5 (Fig. 1). Few hours after the occurrence of the mainshock, the BSI (“Bollettino Sismico Italiano”) working group started to manually analyze P and S phase arrival times and seismogram amplitudes of earthquakes with magnitude M L >= 3.5 recorded by the the Italian National Seismic Network (Rete Sismica Nazionale, hereafter RSN) in order to better constrain hypocenter locations previously provided by the seismic surveillance room of the INGV in Rome for rapid communication to the Italian Civil Protection (Dipartimento Protezione Civile, DPC). Later, the BSI working group analyzed the seismicity of the sequence of the first weeks of seismic activity by revising hypocentral parameters of more than 500 events.