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Asama Volcano, Japan, is one of the most active volcanoes in the Japanese islands. Recent development of geophysical monitoring in Asama Volcano allows us to infer the magma pathway and its structural controls beneath the volcano. Combining geodetic data and precise earthquake locations during recent eruptions suggests that the magma intrudes several kilometres to the west of the summit to a depth of about 1 km below sea level as a nearly east–west-trending dyke. The vertically intruded magma then moves horizontally by several kilometres to beneath the summit before it ascends vertically to make the surface. Combining the P-wave velocity and the resistivity structure shows that the intrusions are under structural controls. Frozen and fractureless magma associated with volcanic activity until 24 000 years ago impedes the ascent of rising magma on its way to the surface. The S-wave velocity structure inferred from ambient noise tomography reveals a low-velocity body beneath the modelled dyke. From independent information, we have inferred that this low-velocity body is likely to be a magma chamber.

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