GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.3 GNGTS 2024 Fig. 2 – a) Map distributon of the earthquakes that show the later seismic phase (green dots), that do not show the x- phase (red dots) and those earthquakes where the presence of the x-phase is unclear (blue dots). Examples of record sectons of the three cases we discuss in the text. The “N.” in the ttle corresponds to number id in the map (N. 40, 38, 41). In the record secton, each vertcal waveform is normalised by its absolute maximum of amplitude, excluding S - waves from the plot and aligned by frst arrival P, at 20 s. Waveforms are sorted by epicentral distances, shown on the vertcal axis. Arrival tmes indicate that the x-phase is not a depth phase, which shows an increasing diference of arrival tme with the P- onset at increasing epicentral distances (Murphy and Barker, 2006). The x-phase is not even a SP- wave which is analysed by Zhao et al. (1997) for the Japan slab. It has an