Volcanic Micro-tremors at the Volcano Aso

(Communicated by Prof. K. Sassa) We investigate the variations and other properties of the micro-tremors at the Volcano Aso observed by the Wichert seismographs in the Volcanolo-gical Laboratory since 1950. In this paper, we treat the first kind and the second kind of the micro-tremors of the four kinds which have been clas-sified by K. Sassa. He studied in decade of 1930 the phenomenon that the micro-tremors stop rapidly before eruptions and again increased after them. This time, we perceive the same phenomenon in the eruptions of Apr., 1953, Dec., 1957, and June, 1958. Next, we can perceive that the values of NS-component/EW-component of amplitudes of the second kind increase from 0 to 1 at the eruptions. It is found that this disposition occured also in the violent eruptions of 1933. Thus, on the assumption that the crack parallel to the row of the present craters, which has been infered from the mode of vibration at the eruption-earthquake by K. Sassa, vibrates after the eruption, being accompanied with the magmatic reservoir, we calculate the azimuthal distributions of amplitudes and indicate that the transversal com-ponent is the same order as the longitudinal component in the direction of the Volcanological Laboratory. 1.