GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.3 GNGTS 2024 Moment tensor inversion of the 1947 Squillace Basin earthquake (Southern Italy) using digitzed analog seismograms S. Scolaro 1* , J. Batlló 2 , B. Orecchio 1 , D. Prest 1 , D. Stch 3 , C. Totaro 1 1.Department of Mathematcs, Computer Sciences, Physics, and Earth Sciences, University of Messina, Italy 2.Insttut Cartogràfc i Geològic de Catalunya, Barcelona, Spain; 3.Insttuto Andaluz de Geofsica, Universidad de Granada, Spain The importance of historical seismic data legacy has amplifed within the scientfc community due to its potental synergy with modern analysis techniques. Seismograms from the analog recording era cover more than a century of seismic actvity, providing signifcant contributons especially in studying regions afected by major historical seismic events and minor actvity in recent decades. We collected and digitzed analog seismograms to investgate the 11 May 1947 earthquake that is, according to the CPTI15 catalog (Rovida et al., 2022), the largest seismic event (proxy Mw 5.7) instrumentally recorded in the Squillace Basin, at the Ionian ofshore of central Calabria. This sector is a high seismic risk area framed in the complex geodynamic setng leaded by the NW- trending Nubia-Eurasia convergence and the southeastward Ionian slab rollback. Moreover, the presence of the lateral edge of the Ionian slab has been suggested and an intense debate is stll open concerning the possible existence and the proper locaton of a Subducton-Transform Edge Propagator (STEP) fault zone. Through a tme-domain waveform inversion algorithm specifcally developed for waveform inversion of analog seismograms (Stch et al., 2005) we computed the frst moment tensor soluton for the 1947 earthquake. Staton bulletns and original seismograms recorded by medium-to-long- period seismographs have been collected, digitzed and properly corrected for geometrical distortons. The moment tensor soluton obtained for the 1947 earthquake indicates a strike-slip mechanism, focal depth of 28 km and Mw 5.1, that represents the frst moment magnitude estmate directly computed from waveform analysis. The result has been accurately checked by performing several inversion tests and interpreted in the frame of the regional seismotectonic scenario (Orecchio et al., 2021 and references therein), where the obtained lef-lateral kinematcs on about WNW-ESE oriented fault are compatble with a STEP fault actvity in the Squillace Basin area. Our study demonstrates the invaluable and irreplaceable role of informaton derived from pre- digital seismograms in providing new constraints for local and regional seismotectonic modeling in high seismic risk regions like the Calabrian Arc. Furthermore, the presented analysis is also useful for sharing within the scientfc community some methodological challenges linked to the management of historical seismograms.