Fig. 2

a Map and vertical-NS cross-sections of hypocenters of volcanic earthquakes determined by KSVO. Vent locations of the 2018 eruptions are represented by red color. A black star shows a reference point for the infrasound waveform plot in Fig. 5 and ASL analysis. b Space–time plot of seismicity at Kusatsu-Shirane in the period from June 2016 to December 2018