Study on generations and propagations of the long-period ground motion from a large earthquake for assessing the effects to a large oil tank and a base-isolated building.

通过对2003年十胜冲大地震时，大油罐飞溅和油罐起火的北海道的汤伏盆地、新泻盆地、为了确定沿着汤抚盆地沿岸的S波速度结构，我们进行了微震阵列测量，包括Tomakomai西港。Tomakomai地震基岩的深度，其中长周期（7秒）的最大振幅。运动被观察到，比东部和西部的Tomakomai浅。一般认为长周期地震动与基岩深度有关，但实际情况是近地表中低速层（Vs ≤ 0.8km/s）对长周期地震动的放大作用最大 关于我们 沉积盆地中的g周期运动。通过对2004年纪伊坂东冲地震和2003年新泻中越地震的地震动观测数据进行空间对比，发现东京湾地区的长周期地震动主要受面波的影响，尤其是10 s以上的面波。在千叶县附近的S波速度结构的调查中，我们还进行了新泻盆地的S波速度结构的调查，其中的长周期运动的意义已经被指出。得到盆地中部由7层组成的结构模型。Vs ≥ 2km/s的基底深度约为5 km，证实了这三个测点的长周期运动占主导地位，其深部沉积层与长周期运动的增强有较好的对应关系。这些地区的地震动估计表明，对于长周期的人工结构，如基础隔震建筑物和大型储罐，迫切需要采取对策。少

We investigated into the generation and propagation of the long-period ground motion from large earthquakes, by conducting surveys of S-wave velocity structures and synthesizing earthquake ground motion at the Yufutsu basin in Hokkaido, where oils sloshed from the large tanks and the tanks were burnt in a fire during the 2003 Tokachi-oki earthquake, the Niigata basin, and the Metropolitan area.We conducted the array measurements of microtremors for determining the S-wave velocity structure along the coast of the Yufutsu basin including the Tomakomai west port. The depth to seismic bedrock at Tomakomai, where the largest amplitudes of long-period (7 sec.) motion was observed, was shallower than those of both east and west Tomakomai. It is generally considered that the long-period ground motion correlates with the depth to a seismic bedrock, however, this is the case that the intermediate near surface layer of low velocity (Vs〜0.8 km/s) plays most significant role in amplification of lon … More g-period motion in a sedimentary basin. We confirmed this evidence by the 2-D simulation of ground motion.We found some features through the spatial comparison of observed ground motions from the 2004 Kii-hanto-oki and the 2003 Niigata Chuetsu earthquakes that the long-period ground motion at the Tokyo bay area were strongly dominated by surface waves, especially that of longer than 10 sec. was prominent near the coast of Chiba prefecture.We also carried out the survey of S-wave velocity structure in the Niigata basin, where the significance of the long-period motion had been indicated. We obtained the structure model consists of 7 layers in the central part of the basin. The depth to the basement layer of Vs〜2 km/s was about 5 km.We confirmed that these three test sites dominated long-period motion and their deep sedimentary layers correlate well with the increasing of long-period motion. The estimated ground motions at these areas indicate that urgent countermeasures are necessary for long-period man-made structures, such as base-isolation buildings and large storage oil tanks. Less