GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.3 GNGTS 2024 Fig. 1 – Observaton of the later seismic phase. a) Statons which recorded the x-phase (green triangles). Seismograms of statons in black do not show the later arrival. Secton trace AB of the Fig. 3, passing from the 2011 earthquake (n. 37). The red lines delineate the old (30 Ma) and the present subducton signature. The two thin black lines delineate the azimuths -60° and 30° startng from the epicentre. b) Time-distance vertcal seismograms of the 2011 event aligned with P arrival tme at 20 s. The red line marks the later phase arrivals. European Integrated Data Archive, 2023 (EIDA, htp://eida.ingv.it/) and from Incorporated Research Insttutons for Seismology Data Management Centre, 2023 (IRIS DMC, htps:// service.iris.edu/ ) . We examined the seismological features of the wave to establish its nature by visual inspecton of the waveforms and record sectons. Later phases observed in a subducton context have characteristc features that allow to discern between the diferent type of waves interactng with the subductng lithosphere. We, therefore, compared the x-phase with seismic waves observed in subducton systems. We fnally reproduced its travel tmes and ray paths in a 2D velocity model with Seis83 sofware (Červený and Pšenčík, 1984) that makes use of ray-tracing technique (Červený et al., 1977). We used IASP91 velocity model (Kennet and Engdahl, 1991) to represent the velocity structure outside the slab. The slab boundaries were constrained by seismicity distributon of the Southern Tyrrhenian Sea, projected in the vertcal secton with trace AB in Figure 1a. According to tomographic studies (e.g., Amato et al., 1993; Scarf et al., 2018), the subductng lithosphere is characterised by positve velocity anomalies. We increased the velocity inside the slab in diferent runs by a percentage between 1.5% and 5% to the IASP91 velocity values. Results