GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.3 GNGTS 2024 First evidence of water transport in the Earth’s mantle from seismograms of Southern Tyrrhenian earthquakes T. Ninivaggi 1 , G. Selvaggi 2 , S. Mazza 2 , M. Filippucci2, 2,3 , F. Tursi 4 , W. Czuba 5 1 Isttuto Nazionale di Geofsica e Vulcanologia, Sezione Irpinia, Grotaminarda, Italy 2 Isttuto Nazionale di Geofsica e Vulcanologia, ONT, Roma, Italy 3 Dipartmento di Scienze della Terra e Geoambientali, Università degli Studi di Bari “Aldo Moro”, Bari, Italy 4 Dipartmento di Scienze della Terra, Università degli Studi di Torino, Torino, Italy 5 Insttute of Geophysics, Polish Academy of Sciences, Warsaw, Poland Introducton We have found a previously unreported later seismic phase in seismograms of European seismic statons from intermediate-depth and deep earthquakes of the Southern Tyrrhenian subducton system. We notced the later phase on seismograms of a deep earthquake occurred in the Southern Tyrrhenian subducton region. The seismic phase, that we called the x-phase , appears few seconds afer the direct P- wave, at statons located some hundreds of km away from the epicentre towards north (Fig. 1). The interest in studying a later phase, detected afer frst arrivals, and observed in subducton zones, is motvated by the possibility to obtain indicatons on the slab propertes (geometry, velocity anomalies, and petrology), because of their interacton with the subductng lithosphere. These later phases could be, for example, waves converted at the upper slab interface from the direct waves (e.g., Zhao et al., 1997) exploited to locate the upper boundary of the subductng plate. Later phases are also the depth phases, exploited to constrain hypocentral depths (e.g., Zhao, 2019). High frequency guided waves have been also interpreted as scatered seismic waves by heterogeneity in plate structure and enhanced by the presence of a metastable olivine wedge (Furumura et al., 2016). As the x-phase is very likely linked to the subducton system, this research verifes the nature and the origin of the wave and gets new insights on the slab features. Data and methods To verify the robustness of the fnding, we made a systematc analysis of the largest intermediate depth and deep earthquakes of the Southern Tyrrhenian subducton system, by selectng the 43 earthquakes occurred from 1990 to 2020 with magnitude ML ≥ 4.5 from the INGV Italian Seismological Instrumental and Parametric Database (htp://cnt.rm.ingv.it/iside ). The depth range is between 100 km and 644 km. The selected seismic statons are from 10° (central Africa) up to 71° North (Cape North in Norway) in lattude and between 10° (Portugal) West and 50° East (Mar Caspio) in longitude. We extracted and analysed about 25,000 digital waveforms from the