多様なシナリオを考慮した地震動評価と建物応答解析
千島海溝沿いの巨大地震を対象とした検討
地震災害に対してレジリエントな社会を実現するためには，被害拡大を防ぎ早期の復旧復興に寄与する耐震性能の高い建築物を設計することが重要となる。現在，高い耐震性能が求められる超高層建築物等では，時刻歴応答解析が行われているが，入力する地震動は，地震シナリオを一意に決めて作成されることが多い。設計における想定外を減らす観点から，今後は震源特性の不確実性に起因する地震動のばらつきを考慮した設計が望まれる。
そこで本報では，千島海溝沿いの巨大地震を対象に，多様なシナリオを考慮した多数の長周期地震動を評価した。また，建物モデルを用いた応答解析を行い，地震動のばらつきが建築物に与える影響を確認した。
その結果，長周期地震動は一部ケースで現行の基準を上回る地震動強さとなり，震源モデルの選択により地震動強さや建物応答に大きなばらつきが生じることが分かった。超高層建築物等の設計にあたっては，これらのばらつきに十分な配慮が必要となる可能性がある。
キーワード：長周期地震動，建物応答，千島海溝沿いの巨大地震，震源特性の不確実性，スーパーコンピュータ「富岳」
＊１ 技術センター 都市基盤技術研究部 防災研究室
＊２ （国研）海洋研究開発機構
Evaluation of Long-Period Ground Motions and Building Responses Based on Multiple Fault Rupture Scenarios
Study on Megathrust Earthquakes along the Kuril Trench
In order to achieve a society that is resilient against earthquake disasters, it is important to design buildings with high seismic performance that can prevent widespread damage and contribute to early recovery and reconstruction. Currently, time history response analysis is employed for the design of high-rise buildings that require high seismic performance. However, the input ground motions are often generated based on a uniquely determined fault rupture scenario. In order to ensure that phenomena that would normally be unexpected are properly covered in design, it is desirable to perform the design taking into consideration the variation of ground motions caused by uncertainties in the seismic-source characteristics.
In this study, numerous long-period ground motions for megathrust earthquakes along the Kuril Trench were evaluated, taking into consideration various scenarios. In addition, building response analysis was conducted to evaluate the response characteristics and to determine the effect of variations in ground motions on the building.
The results showed that long-period ground motions exceeded the current building codes in some cases, and that the choice of source model caused large variations in seismic intensity and building response. These variations should be given careful consideration in the design of high-rise buildings.
Keywords: long-period ground motion, building response, megathrust earthquakes along the Kuril Trench, seismic-source uncertainty, supercomputer Fugaku
*1 Disaster Prevention Research Section, Urban Engineering Research Department, Taisei Advanced Center of Technology
*2 Japan Agency for Marine-Earth Science and Technology