Observation and Discussion of the Present Seismic Activity of Volcano Huzi

Abstract

Among 47 active volcanoes in Japan which have historical records of eruption, 17 volcanoes are under continuous instrumental observations by Japan Meteorological Agency and several Universities. The remnant active volcanoes, namely, 30 in number, being left from continuous volcanological observation. Several of them have been studied on some occassions in short period from geophysical point of view, however, scarcity of quantitative observation for most of these volcanoes makes it impossible to estimate the future volcanic risk. For instance, Volcano Huzi which made violent volcanic eruptions in historic time has still possibility to have future volcanic activity. Volcano Huzi is located near densely populated cities, where inhabitants are thus exposed to likely future volcanic violence. However, we have no detailed data of the present seismic activity there. Thus, we came to choose Volcano Huzi for precise seismic observation in order to know the present seismic activity of Huzi itself. Six seismic stations were set up during Oct. 3∿13, 1965 by the research group of five universities. High magnification seismographs at each station recorded several small shocks originating from Huzi. Epicenters of these earthquakes were determined as located at southern flank of the volcano with the focal depth less than 10 km. Beside these earthquakes, seismic stations at the southern flank of the volcano recorded small shocks of volcanic origin which were not observed at other stations. From these observational facts, we concluded that 1) present seismic activity of Volcano Huzi is quite low compared with other active volcanoes in Japan, and 2) seismic activity of volcanic origin seems to be concentrated at the southern flank of the volcano.