関東・濃尾・大阪平野での長周期地震動シミュレーション
2004年紀伊半島南東沖地震による検証と想定東海・東南海連動地震の予測
本研究では，関東，濃尾，大阪平野を含む3次元地盤モデルを構築した。大規模有限要素法（FEM）により，スーパーコンピューターで周期2.5秒以上の長周期地震動の計算を行なった。
まず最初に，2004年紀伊半島南東沖地震の前震のシミュレーションを行った。観測記録に見られる長い継続時間や，平野における地震動の増幅，スペクトル特性を良好に摸擬することができた。これにより，3次元地盤モデルが長周期地震動を評価する上で信頼できるものであることを確認した。
次に，想定東海・東南海連動地震のシミュレーションを行った。中央防災会議の震源モデルをベースに，滑り分布と破壊伝播時刻の不均質性の導入も行った。また，破壊伝播速度や破壊開始点の影響も検討した。大阪平野の此花で7～8秒，濃尾平野の名古屋で3.5秒，関東平野の新宿で8.5～9秒に中心周期を持ち，告示スペクトルを上回る卓越成分が見られた。
| キーワード： | 設計用入力地震動，長周期地震動，超高層ビル，東海地震，東南海地震 |
＊１ 技術センター 建築技術研究所 防災研究室
＊２ 技術センター 技術企画部 情報技術室
Long-period Earthquake Ground Motion Simulations for the Kanto, Nobi, and Osaka Plains and Surrounding Regions
Verification by the 2004 Off the Kii Peninsula Earthquake and Prediction for the Tokai-Tonankai Earthquake
We constructed a large-scale model of the subsurface ground including Kanto, Nobi, and Osaka plains. Using this model, we calculated the long-period ground motions with periods longer than 2.5 seconds by the large-scale finite element method on our super computer.
First, we simulated the foreshock of the 2004 Off the Kii peninsula earthquake in order to verify our subsurface ground model. The simulated ground motions agreed with observed ground motions in terms of the long duration of the waveform, the amplification in the plains and the spectral characteristics. The results show that our subsurface ground model can reliably evaluate long-period ground motions.
Second, we predicted the ground motions of the expected Tokai-Tonankai coupled earthquake. We constructed the source model based on the one proposed by the Central Disaster Prevention Council, Cabinet Office of the Japanese government. We took into consideration the heterogeneous slip distribution and zigzag rupture propagation. We also studied the effect of the rupture velocity and the location of the rupture’s starting point. The pseudo velocity response spectra at Konohana in the Osaka plain has a significant peak at around 7 to 8 seconds, while that for Nagoya in the Nobi plain has a peak with a period of 3.5 seconds and that for Shinjuku in the Kanto plain has a peak at around 8.5 to 9 seconds. These peaks in the pseudo velocity response spectra surpass the uniform design spectra regulated by the Building Standard Law.
| Keywords: | design earthquake ground motion, long period earthquake ground motion, high-rise building, Tokai earthquake, Tonankai earthquake |
*1 Disaster Prevention Research Section, Building Engineering Research Institute, Technology Center
*2 Information Technology Section, Planning Department, Technology Center
