Fig. 17

Infrasound observed at the Aso volcano, Japan, on April 21, 2015 (JST) (Ishii et al. 2019). a An example of a waveform (detrended). b Spectrogram of (a) (time window 2.56 s, overlap 2.50 s). c Power spectrum (smoothed) of (a) (event#6), stacked spectrum of 10 events during 19:07:10 - 19:51:00 (JST), background between the events (19:26:00 - 19:26:30). Arrows indicate the peaks at 0.5, 2.2 Hz, and the 3.5 - 16.5 Hz band