Fig. 1

Topographic map of the study area and computational mesh used in the three-dimensional resistivity inversion. a Topographic map of Hakone volcano, Central Japan, highlighting the spatial distribution of the magnetotelluric observation sites used in this study. The blue, green and red plus symbols indicate the 2011 AMT observations, the 2013 AMT observations and the 2010 and 2011 WMT observations, respectively. The topography was extracted from a 10-m DEM provided by the Geospatial Information Authority of Japan. The epicentres of the earthquake swarms from April to October 2015, as determined by Yukutake et al. (2017), are plotted as black dots. The black dotted line indicates the caldera rim of Hakone volcano. The orange diamonds mark the Owakudani geothermal area, central cones (Mts. Kamiyama and Komagatake) and Mt. Kintoki. The surface extent of Lake Ashinoko is shown in blue. b Subsurface computational domain without air elements. The origin of the mesh was set at the sea level just beneath Mt. Kamiyama. The tetrahedral lattice in the central portion of the computational domain, covering the core region of Hakone volcano and encompassing all the MT/AMT sites, was made at a finer resolution. The green, red and blue colours indicate the elements located in land, seawater and lake water, respectively. c Surface mesh around the core region. The tetrahedral lattice was subdivided into an even finer mesh around the AMT/WMT sites