阿蘇山の火山性長周期微動の振動様式と振幅別頻度分布について

概要

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For the purpose of investigating the properties of the long-period tremors of Aso volcano, Kyushu, an electro-magnetic long-period seismometer (T=10 sec, V=500, and 3 components) was installed at the Asosan Weather Station, from Oct. 23, 1982 to March 13, 1984. During the 2.5 years, the number of the tremors with amplitude of 2μ or larger amounted to 502, and each tremor had the wave train with 6-10 sec. in period. On the basis of the analysis of the particle motion of the tremor, it is found that the motion shows strong directivity, and the tremors seem to propagate from the E13±2°N direction. If the tremors, accordidg to the results of SASSA (1935), consist of body wave, the incidence angle of tremor is estimated as 54±3°. These results suggest that the tremors propagate from or through the region of 910±130 m in depth beneath the border between the Second and the Third crater of Nakadake. With respect to the maximum amplitude-frequency relation of the long-period tremors, the log-amplitude vs. log-frequency curves are non-linear, and bent downward at 2μ in amplitude (UD component). The m-value are obtained as ca. 5 in the amplitude smaller than 2μ, and ca. 8 in the larger one. The latter is conspicuously large compared with the values obtained in other volcanoes. This fact gives evidence that the long-period tremors have some limited magnitude.
特定非営利活動法人日本火山学会の論文
1985-07-01