阿蘇カルデラ周辺の表層電気伝導度分布

Abstract

The authors carried out VLF-MT survey in and around Aso Caldera. Conductivity distribution within the Aso Caldera shows two typical features; caldera floor has almost homogeneous and high conductivity (> 100μS/cm), while the post caldera cones show wide range. Most cones have lower conductivity (<30μS/cm), except around Naka -dake Craters and western flank of post caldera cones (>300μS/cm). In the northern caldera floor, extremely high conductivity (>500μS/cm) was found along the NNW-SSE line from Uchinomaki to Mietsuka. This indicates hydrothermal water is supplied along this line. High conductivity in the caldera floor can be explained by mixture of rain water and hot spring waters. Emission rate of SO2 by hot springs is estimated 32, 000 t/yr. This value is 18% of the emission rate by fumaroles in the Naka-dake Crater. Most of high conductivity areas around Aso Caldera correspond tectonic fault.