Fig. 10

The region containing the sources of the continuous tremors is an inclined cylinder. a Weighted centroid of estimated CT source locations (\(N_{\mathrm {p}} = 10\); black circles in Fig. 9) at each depth with a disk size (horizontal bar). The results are projected on a vertical plane perpendicular to the strike direction of the crack (gray area; Yamamoto et al. 1999). The distribution of these disks consists of an inclined cylindrical region (dip is \(80.7^\circ\); inserted sketch). Wiggly lines indicate the flow direction of the volcanic fluid. b–e Horizontal distribution of both the apparent disk area of the cylindrical region (thick circle) and all estimated source locations (thin circles) at depths of 0, 100, 200, and 300 m, respectively. The size of each thin circle indicates the number of crossovers. The total number of source estimations (30-min windows) is shown in the lower right. The hatched area corresponds to a fumarolic zone at the southern crater wall (Fig. 2). The wiggly lines in e show the flow directions not only at a depth of 300 m, but also in the entire region of the crack