地震計と赤外線放射温度計による三原山の噴火の同時観測 : I. 観測結果

抄録

Small eruptions have continuously taken place on the Miharayama Volcano from February 28 to the end of June 1974. An infrared radiation thermometer and a vertical type seismometer were set on the crater-rim of the Miharayama Volcano and series of eruptions were observed on June 12, 1974. Electrical signals of the radiation energy coming from the craterlet at the time of eruptions and seismic signals following the eruptions were simultaneously recorded in a data-recorder. An instant of eruptions of hot materials enable accurately to determine from the pulse which have recorded by the infrared radiation thermometer. From the analysis of the observational data the following results were obtained : The observed seismic signal which has been so called “isolated type eruption-tremor” is characterized by distinct phases : namely P₁-, P₂-, Q- and X-phases. Q-phase exactly corresponds to the time of eruption. P₁-phase precedes about 6-10 sec. and P₂-phase precedes within 5 sec., while, X-phase is delayed by 4 to 30 sec. from the time of eruption. P₁-and P₂-phases are always accompanied with the eruption, while, X-phase is not always followed to that. There are the periodicity of 40 sec. or 80 sec. between two succesive tremors or eruptions. Ishimoto-Iida’s statistical formula for the frequency distributions of maximum amplitude does not adapt for the observed eruption-tremors. Downward initial motions were observed in the every phases of the eruption-tremors, but there are some exceptional cases for the P₁, P₂, Q-phases.