著者

関口 春子 浅野 公之 岩田 知孝

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.125, no.10, pp.715-730, 2019-10-15 (Released:2020-01-10)

参考文献数

48

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将来の地震の地震動予測をより高精度にするため,既往の知見と既往の物理探査・地震観測データを融合して奈良盆地の堆積層の3次元速度構造モデルを構築した.奈良盆地は,大都市圏に比べ地下構造の探査情報が少ないが,盆地を埋積する堆積層には大阪盆地のそれと共通性があると考えられるため,大阪盆地の3次元速度構造のモデル化で培われた知見や技術を利用して奈良盆地の3次元モデルを構築した.重力異常から推定された基盤岩深度と盆地中央部のボーリングで得られた大阪層群の海成粘土等の情報を組み合わせて3次元の堆積年代構造のモデルを作り,これを経験式で地震波速度と密度に変換した.奈良盆地にはPS検層による直接的な速度構造情報は無いが,微動観測からの情報を用いることにより,地震動応答の面でもモデルの拘束や検証を行った.また,実小地震の波形モデリングと強震観測記録の比較から,地震動再現能力を確認した.

著者

岩城 麻子 岩田 知孝 関口 春子 浅野 公之 吉見 雅行 鈴木 晴彦

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.61, no.4, pp.161-173, 2009

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We studied the source model and the underground velocity structure model for quantitative estimation of long-period (3-20s) ground motion in the Oita Plain due to a hypothetical Nankai earthquake. First, the deep subsurface velocity structure of the Oita sedimentary basin was validated by a long-period ground motion simulation of the 2000 western Tottori earthquake records. The simulated waveforms reproduced the amplification and duration of the observed waveforms and peak periods of pseudo response spectra at strong motion stations both in and out the Oita Plain reasonably well. Then we combined the subsurface velocity structure with a crustal velocity structure and performed long-period ground motion simulations of a Nankai earthquake by a three-dimensional finite-difference method. The source model has a total area of 34,000 km<SUP>2</SUP> with total seismic moment of 6.24&times;10<SUP>21</SUP> Nm (<I>M</I><SUB>W</SUB> 8.5). In addition to the scenario in which rupture propagates from the east (east-hypo model) that have been generally accepted, we investigated another from the west (west-hypo model). For the east-hypo model, the maximum amplitudes of the simulated horizontal ground motion in the Oita plain was three to four times as large as that on a rock site beside the plain. Especially in the bay area, the maximum ground motion reached 100cm/s and the pseudo velocity response spectra at period 6-8s were more than 400cm/s. On the other hand, the ground motion simulated by the west-hypo model was roughly one fifth smaller than that by the east-hypo model. It is also pointed out that in the east-hypo model simulation, the seismic waves generated by the two asperities near to the Oita plain are enlarged due to the directivity effect and amplified and prolonged by the sedimentary basin structure.