阿蘇火山中岳における主な爆発活動と火山性微動の関係 : ウィーヘルト地震計に見られる振幅変化

抄録

Aso Volcano is one of the active volcanoes in Japan. Seismic wave associated with volcanic activity had been recorded by Wiechert seismograph at Aso Volcanological Laboratory, Kyoto University from 1928 to 2000. Some records of volcanic tremors related to large-scale explosive events had been already analyzed, however, many events were not yet examined. In this study, the previous volcanic activities with explosion are re-examined and classified into the following four types based on the seismographic record: (A) The amplitude of tremor was small prior to an explosion. After the explosion, the amplitude of tremor increased; (B) A phreatic explosion suddenly took place without any precursory signal. The tremor amplitude was less than 3μm before the phreatic explosion, and then decreased to be less than 0.5μm after the explosion; (C) An explosion occurred after decreasing in amplitude of volcanic tremor. After explosion, volcanic activity had been increasing; (D) The volcanic tremor was increasing and changed into continuous tremors. An explosion occurs among continuous tremor. In Nakadake crater, types C and D are major types of volcanic activity after 1963. The above classification could be an important criteria for the prediction of eruption at Aso Volcano.