Fig. 5From: Temporal variation in source location of continuous tremors before ash–gas emissions in January 2014 at Aso volcano, JapanSpectrograms of continuous tremors. Spectrograms of recorded seismic signals at a SUN and b KAEB calculated in an eight-hour time window with a four-hour overlap. Data gaps shown in white are caused by, for example, seismometer/digitizer failure or errors in data transmission. Black rectangles spanning from 1 December 2013 to 20 January 2014 at a frequency band of 5–10 Hz indicate the data to be analyzedBack to article page