Fig. 1

Maps of Hakone volcano. a Distribution of seismic stations in and around the caldera. The study location is indicated by the red rectangle in the inset map. The bold line indicates the rim of the caldera. Gray lines show the detailed topography of Hakone volcano. b Magnified map of the area around the Owakudani geothermal region. The red dot indicates the location of the vents that formed during the phreatic eruption (Mannen et al. 2015). The orange region indicates the area of ground uplift detected by SAR interferometry that started 2 months before the eruption (Doke et al. 2015). The red rectangle indicates the location of the open-crack source oriented NW–SE that was estimated by the tilt change (Honda et al. 2015)