Fig. 7
Precursors of the 2014 phreatic eruption. a Horizontal distance of detected VT earthquakes from 11:30 to 12:00 JST on 27 September 2014, projected onto the strike of the hypocenter alignments (N15W-S15E). Circles are scaled to magnitude and color-coded to depth. Black dashed lines approximate the locations of the fronts of earthquake migrations. b Depth variations in VT earthquakes, colored to depth. Circles are scaled to magnitude. Black dashed lines approximate the locations of the fronts of earthquake migrations. c Bandpass-filtered waveform between 4 and 12Â Hz (black curve) and envelope between 1 and 4Â Hz (red curve) recorded at the V.ONTN station. d Time series of tiltmeter records observed at the V.ONTN station. NS and EW components denote the northward and eastward ground-up components, respectively