Fig. 1

a Map showing the location of the seismic reflection survey (solid black line) undertaken by Matsumoto et al. (2012). Thin black dashed lines represent faults in the graben, and gray circles indicate pressure sources inferred from leveling and GPS data (Kohno et al. 2008). Figure courtesy of Matsumoto et al. (2012). b Broadband magnetotelluric (MT) observation sites. Map area is indicated by the rectangle in a. Faults (after Tsutsumi 2015) are represented by blue lines with teeth. CF is the Chijiwa Fault, KF is the Kusenbu Fault, and OF is the Oshidorino-Ike Fault. Other lines are minor or unnamed faults. Pressure sources are as in a. Younger lava domes (No Nodake, My Myokendake, Fg Fugendake; Hoshizumi et al. 1999) are indicated by yellow triangles