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Fig. 3 | Earth, Planets and Space

Fig. 3

From: Analyzing the continuous volcanic tremors detected during the 2015 phreatic eruption of the Hakone volcano

Fig. 3

Seismic record from OWD station during the eruption. a Spectrogram of the vertical ground velocity from 3:00 on June 29 to 7:00 (JST) on July 1, calculated by using a 40-s time window with 20-s intervals. The instantaneous increases in amplitude within a wide frequency range correspond to signals from VT earthquakes, whereas the continuous signal within the region framed by the box is due to the volcanic tremor. b Root-mean-square amplitude of the filtered vertical ground velocity (1–6 Hz) using a 1-min time window (red line). In order to mitigate contamination by VT earthquakes, signals from earthquakes were deleted using an auto-detection algorithm based on the short-term average/long-term average ratio. The vertical orange lines and horizontal blue bars indicate impulsive infrasonic wave counts per minute and the vent formation times (Mannen et al. 2015), respectively. The numbers on the blue bars show the index number of vents defined in Mannen et al. (2015). The green line indicates the cumulative number of VT events that occurred during this period

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