Fig. 1

Map of the target area. a Location of Myojin Knoll caldera in the Izu-Ogasawara arc, with the inset showing the location of the Japanese Islands. The white and red circles, respectively, denote the locations of basaltic and rhyolitic volcanoes (Tamura et al. 2009). The yellow star denotes the location of Myojin Knoll caldera (a rhyolitic volcano). b Plan view of Myojin Knoll caldera. The yellow box denotes the survey area of the present study shown in (c). The color scale is explained in the legend below. c Magnified plan view of the survey area. The color scale is the same as (b). The location of the Sunrise deposit (Iizasa et al. 1999) is marked by the thick dashed curve. The locations of a low-magnetization area, ridge-like structures, and scarp structures (Honsho et al. 2016a) are marked, respectively, by a dot-dashed curve, thin dotted curves, and inverted Ts