| 講演要旨(和文) | | 2016年4月16日に，熊本地震の本震（MJMA 7.3）が発生し，いくつかの強震観測点で周期２〜5秒の帯域の加速度応答値が800 cm/s2を超える長周期地震動が観測された．この熊本地震のような内陸地殻内地震において長周期地震動が観測された事例は少なく，その成因を解明することは長周期構造物の耐震性を考える上で非常に重要である．そこで本報では地盤震動特性に着目し，長周期地震動が観測された3つの観測点において実施された微動アレイ観測の結果からS波速度構造を推定した．さらに，推定されたS波速度構造から各観測点の地盤増幅特性を算出した．その結果，算出された地盤増幅特性はいずれも周期２〜５秒の帯域で大きな増幅特性を持ち，熊本地震時に観測された長周期地震動の成因の一つとして地盤増幅特性が強く影響していることが明らかになった． |
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| | 講演要旨(英文) | | On April 16, 2016, an inland crustal earthquake (MJMA 7.3) occurred in the Kumamoto prefecture. Several strong motion stations recorded long period ground motions with response acceleration in the period range from 2 to 5 seconds exceeding 800 cm/s2. It is rare that these long period ground motions were observed during the inland crustal earthquake, and it is very important to elucidate the cause in considering the earthquake resistance of long-period structures. Therefore, in order to understand the cause of these long period ground motions during this earthquake, we focused on the site effects. We carried out microtremor array observations at three stations which recorded the long period ground motions, and estimated the underground velocity structures. And then, based on them, we calculated site amplification characteristics. As the result, it was found that the site effects strongly influence the long period ground motions observed during the 2016 Kumamoto earthquake because calculated site amplification characteristics have large amplification factors in the period range from 2 to 5 seconds. |
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