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 : II. 現象の解析と解釈

抄録

Series of small eruptions frequently took place on the Miharayama Volcano from Febmary to June 1974. 0n June 12, eruption phenomena were simultaneously observed by means of an infrared radiation thermometer and a vertical type seismometer. As mentioned in our previous paper, four phases, named P_1-, P_2-, Q_- and X-phases were distinctly recognized in an isolated type eruption tremor. In this paper, some characteristics and the source mechanism of the four phases were examined and discussed. In the case of the P_1-, P_2- and Q-phases, similar broad spectra having a peak frequency of 4.6 Hz have been taken, while in the case of the X-phase, a simple spectrum having a peak frequency of 3.2 Hz which is characterized by a damping oscillation with a small damping coefficient (h=0.2～O.3) has been taken. From the consideration of the initial motion of the Q-phase and the time difference between the emission time of magma and the arrival time of the Q-phase, an asymmetrical push cone type model representing a rapid upward force is acting at the origin of eruption beneath the pit crater, is preferable for the mechanism of the Q-phase.