周期特性(3-15秒)を考慮した日本各地における地震動の増幅度分布〔英文〕
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概要
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The increasing number of structures with long natural periods (between 3 sec and 15 sec) makes it necessary to study the strongmotion characteristics in this period range. The damping coefficient of these objects is small and it may cause serious damage at the resonance period. The authors propose the method for estimating the site amplification factors in terms of period by analyzing the large number of strong-motion displacement records of the Kita-Mino earthquake of August 19, 1961, Japan. The observed spectra corrected for the geometrical spreading of surface waves and attenuation factor were compared with the synthetic spectra computed utilizing the normal mode solution. Good agreement was obtained between observations and synthetics at the stations close to the epicenter which are located on the standard crustal structure, so that the difference between the observed and synthetic spectral amplitudes at the other stations reflect the site amplification factor. The site amplification factor, ratios of observed spectra to synthetics, distribute from 0.3 to 14. At certain sites, they strongly depend on period.固有周期が数秒から10数秒に至る長周期構造物,例えば大型石油タンク,長大橋,高層ビル等は年々増加の傾向をたどっている.しかし,これらの構造物の耐震安全性を検討する際に,基礎資料となる長周期の地震動の性質については,十分把握されているとは言い難い面がある.加速度記録の解析を通じ,地震動の平均像あるいは地盤での増幅特性に関する研究から,短周期地震動に対する知見は比較的多いが,上記の周期帯に関してはこの限りではない.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,Earthquake Research Institute, University of Tokyoの論文