Fig. 6.

Result of cosmic-ray muon imaging of the 1944 Usu lava dome. (a) exterior shape of the lava dome and the mound (now converted with trees) viewed from the detector site Mu, (b) the top panel shows the comparison of the zenith-angle dependence of the total; muon count with the numerically estimated angular dependence. The data for muons arriving from the backward direction are also used to confirm the detector efficiency. The vertical viewing angle for “backward-directed” muons is smaller than that for “forward directed” muons due to a tilted emulsion plane; (c) the volume (path length distribution) of the lava dome estimated by means of the topographies; (d) the cosmic-ray muon transmission image; (e) the average density distribution is projected on the cross sectional plane that is parallel to the detector plane and includes the dome peak. The coordinate at the right side indicates elevation in m.