阿蘇カルデラ南郷谷における反射法地震探査

概要

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Results of a seismic reflection survey in a southern valley of Aso caldera, central Kyushu, Japan are described in this paper. The survey includes two seismic lines, one along a radial direction and the another along a tangential direction of the caldera for a purpose to survey the depth to the caldera bottom. These lines are arranged to intersect with each other. A section of the radial line shows a dipping structure towards central cones of the caldera. The radial line is concluded as crossing over the intrinsic rim of caldera in its deeper portion and being laid through a transient structure between a fan and lake deposits in its shallower portion. In contrast with the radial section, the tangential section shows a simple and flat structure. Two well defined reflectors are obtained in these seismic sections. The lower reflector, which is estimated as a top face of the Pre-Aso volcanic rocks, declines steeply towards the central cones and becomes ambiguous in the central-cone side of the radial line. A depth of the lower reflector is estimated as more than 500 m below the surface in the central-cone side. The upper reflector underlies whole area of this survey in a depth about 100 m to 150 m, which is interpreted as the interface in caldera fill. The upper reflector implies a cycle of submergence and emergencies in this area.
特定非営利活動法人日本火山学会の論文
1997-08-31