Fig. 1

Topographic map of the study area and computational mesh of the central part used in the three‑dimensional (3-D) resistivity inversion. a Maps showing the location of Mt. Tokachidake (inset) and local topography (red relief image map). b Topography of the area around the core region of the computational domain and spatial distribution of the magnetotelluric measurement sites used in this study. The contour interval is 50 m. The black circles, red stars, green diamonds, blue inverted triangles, and black crosses indicate the 2009, 2014, 2015, and 2016 audio-frequency magnetotelluric (AMT) observations, as well as the 2016 WMT observations, respectively. c Surface mesh around the core region