Analysis and numerical simulation of seismic events recorded in the ventilation shaft at the Mizunami URL

瑞浪超深地層研究所換気立坑で観測された地震動の分析と数値解析

新美 勝之*; 小林 伸司*; 延藤 遵*; 松井 裕哉 ; 山本 勝

Niimi, Katsuyuki*; Kobayashi, Shinji*; Nobuto, Jun*; Matsui, Hiroya; Yamamoto, Masaru

原子力機構は日本において地下の研究施設の建設を伴う研究プロジェクトを進めている。本研究では、地下の研究施設内に設置した加速度計による地震動のモニタリングにより観測された6つの地震時の加速度波形の記録を分析し、地震動は地表に近くなるにつれ増幅すること、地震波の伝搬特性は南北と東西方向で異なる可能性があることが明らかになるとともに、地表構造物が地上の地震動観測に影響を及ぼしている可能性があることがわかった。さらに、SHAKEと呼ばれる数値解析法を用いた地震動解析と実測結果と比較した結果、解析結果と実測結果はよく一致し、解析手法の妥当性がおおむね確認できた。

JAEA has been conducting geoscientific research and development at underground research laboratories under construction in Japan. In this study, frequency and wave propagation characteristics were analyzed using seismic records for six earthquakes obtained with the seismometers in URL. It was found that seismic motions were amplified from the deep underground to the shallow surface and that the wave propagation characteristics were different in NS and EW directions. It was also assumed that the recorded data of the seismometer on the ground might be influenced by aboveground structures. Then, numerical simulations using SHAKE, which is commonly used for seismic response analysis in Japan and had been applied to the earthquake resistance design in Phase I, were carried out to compare analytical results and observed records. The results showed that the calculated results agreed well with those observed when epicenters are close.