九重硫黄山における熱流量と微動との関係

抄録

Kuju Volcano is situated at the north-eastern direction of Aso Volcano. The distance between them is about 25 kilometers. Kuju-Iwoyama is an explosive crater of Mt. Hosshoyama which is one of the Kuju Volcano group and shows the most intense geothermal (mainly fumarolic) activity in Kuju Volcano. Phreatic explosions occurred in historic ages. At present geothermal activities are shown in the three regions. Observations were conducted in the two of them. In this paper, they are called conveniently the A-region which contains the Chotaro fumarole and the B-region which contains the Hidaira fumarole. Heat flow containing conductive and convective parts was estimated by using the thermal images and the equation of heat balance of the ground surface. Total heat discharges in the A- and the B-regions were estimated at (6.0～6.6)×10⁶ cal/sec and (1.2～1.4)×10⁶ cal/sec, respectively. Average heat flows in the A- and B-regions were 7300～8100 HFU and 9800～11000 HFU, respectively. Anomalous high seismic noise level of several tens of Hz was observed in the A- and B- regions. They may be caused by geothermal activities. The seismic noise was body wave and the depth of the origin was estimated to be less than 10 meters. In addition, very high frequency (about 100Hz) seismic noise was also observed. It may be surface wave. Predominant frequencies and amplitudes of seismic noise of several tens of Hz have a close correlation with the surface heat flow. Heat is transferred mainly by fume in this area. These results suggest that the origin of high seismic noise level is the motion of fume.