Extended Data Fig 6: Alignment of events with P-wave arrivals using vertical spectral envelopes.

a, All events with P-wave energy aligned on a reference line; events are equally spaced sorted by distance; for each event we indicate the frequency band used to derive the spectral envelope and the amplification used in the display, so that all P waves have the same amplitude; glitches and the following S-wave are blanked out. b, P-wave envelopes overlapped for four of the events in the left panel; envelope amplitudes are re-scaled to show the similarity; S0173a and S0235b have clear P- and S-wave arrivals, while we observe only a strong first phase for S0183a and S0205a, interpreted as P-phase, and a weak second phase, interpreted as S-phase. The colour code of the events is the same used in Fig. 3. The spectral window length in b is 40 s to increase the visibility of the S-wave onsets.