摘要：AMT and MT surveys were conducted to investigate at high resolution the spatial resistivity structure of Unzen volcano, with consideration given to understanding its regional dimensionality.Our phase tensor analysis supports the conclusion that the resistivity structure is two-dimensional, with the strike in the E-W direction.Two-dimensional inversions suggest that Unzen volcano is likely to comprise 4 layers: a high resistivity surface (greater than 1000 Ω m), an intermediate second layer (20 to several hundreds of Ωm), a low resistivity third layer (less than 20 Ω m), and a relatively high resistivity basement.We assume the upper-most high resistivity layer consists of undersaturated lava and pyroclastic flow deposits.The second and third layers are likely to be water-saturated and form an aquifer that seems to correlate well with the emergence of groundwater discharge at the surface.In deeper areas beneath the summit, a region with a resistivity of 20–80 Ω m is surrounded by areas of extremely low resistivity (less than 3 Ω m); this structural features in Unzen volcano was first identified in this study, but is typical of the resistivity structure observed in active volcanoes.Interpreting the results of well logs and geodetic studies of Unzen volcano in light of the findings of the present study and the resistivity structure of other active volcanoes, we suggest that Unzen volcano possesses a hydrothermal system of high-temperature fluids beneath its edifice; this hydrothermal system may play a non-negligible role in controlling heat and mass transfer in the magmatic system of Unzen volcano. Key words Unzen volcano resistivity structure Unzen graben aquifer volcanic fluids hydrothermal alteration conduit.
