Seismic Activity and Thermal Process Beneath the Kuju-Iwoyama Fumarolic Area, Central Kyusu, Japan

Abstract

There are four active volcanoes, that is, Tsurumi, Kuju, Aso and Unzen in central Kyushu Japan(Fig.1). The latter two volcanoes have erupted in historic ages. But only phreatic explosions occurred in the former two volcanoes. The Kuju volcano group is composed of many lava domes and a strato volcano. The main rock type is hornblende andesite(VSG and IAVCEI,1971). Kuju-iwoyamais an explosive crater of 'Ht.Hosshoyama of the group and shows the most intense geothermal (mainly fumarolic) activity in central Kyushu. The Otake and Hatchobaru geothermal power stations are 5 km west of the fumarolic area. Based on the measurement of heat and mass discharges, we proposed a simple thermal model for the area (Ehara et al.,1981). Recently we conducted a microlarthquake observation in order to clarify the seismic activity and the undeground structure beneath the fumarolic area. As a result, an active seismic zone and an anomalous structure were observed just beneath the fumarolic area. In this paper. we tried to propose a thermal model to satisfy the observed thermal and seismological data.