Fig. 5From: Analyzing the continuous volcanic tremors detected during the 2015 phreatic eruption of the Hakone volcanoExamples of amplitude spectra for the vertical ground velocity waveforms at OWD station during the volcanic tremor (blue and red) and the noise record (gray). Each spectrogram was calculated using a waveform of 650 s that was smoothed using a Parzen window with a passband of 0.2 HzBack to article page