著者

島 坦 野村 文生

出版者

信州大学工学部

雑誌

信州大学工学部紀要 (ISSN:00373818)

巻号頁・発行日

no.31, pp.87-103, 1971-12

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The analysis was made of the microtremors which were observed at 13 stations in the area surrounding the Takabayama tunnel destroyed by the landslide in January, 1970. The predominant period of microtremors is determined from the spectra, which is used to illustrate the dynamic behavior of underground structure. As given in Table 1, the predominant period of about 0.3 to 0.5 sec. estimated in the shorter period range agrees to that generally observed in the mountains overlaying soft soil. Moreover, another predominant period is found to be about 1.0 to 1.2 sec. in the longer period range of the same spectra. From the correlation of the two predominant periods at each station shown in Fig. 4, it may be considered that the periods of about 0.3~0.5 sec. and about 1.0~1.2 sec. are corresponding to the first and the second mode oscillations in the underground structure respectively. The relative variation of spectral amplitude with the location of observation is discussed mainly for the two predominant periods, and is explained to be caused by the effect of viscosity in the superficial layer on the lower medium. It seems that the coefficient of viscosity varies from about 5 × 10v to 5 × 10v CGS on the boundary of the landslide area, the value in the moutain range being smaller than in the plain.