Fig. 1: Survey area around Kuju volcano.

a Topographic map of Kyushu Island, southwest Japan. b Enlarged view of the Kuju area with geometry of 3D active-source seismic survey and dense seismic network. The white rectangle outlines the 3D active-source seismic survey area (i.e., the gridded zone used for 3D seismic analysis), and the white numbers indicate the inline and crossline numbers. Gray rectangle in b indicates the area shown in Fig. 3. The base map is a 10-m-mesh digital elevation model published by the Geospatial Information Authority of Japan55. These figures were adapted from Tsuji et al.56 and generated using the Generic Mapping Tools57.