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.

为了研究大地震的长周期地震动的产生和传播，我们在北海道裕福子盆地进行了S波速度结构的测量和地震地面运动的合成，在2003年东京地震期间大型储油罐的石油晃动和储油罐的火灾中被烧毁的地方，新泻盆地和都会区。我们进行了包括Tomakomai西港在内的裕福子盆地沿岸的微震台阵测量，以确定S波的速度结构。在Tomakomai的地震基岩深度，那里的长周期(7秒)的振幅最大。观察到的运动，比东部和西部的Tomakomai都要浅。一般认为，长周期地震动与地震基岩埋深有关，然而，低速(vs~0.8 km/S)的近地表中层对Lon…的放大作用最为显著。沉积盆地中的G周期运动较多。通过对2004年Kii-hanto-oki和2003年Niigata Chuetsu地震观测到的地面运动的空间对比，我们发现东京湾地区的长周期地面运动强烈地以面波为主，尤其是大于10秒的地面运动。我们还在新泻盆地进行了S波速度结构的调查，指出了长周期运动的意义。得到盆地中部由7层组成的构造模型。VS~2 km/S的基底层深度约为5 km，证实这三个试验点以长周期运动为主，其深部沉积层与长周期运动的增加有很好的相关性。这些地区估计的地面运动表明，对于长期的人造结构，如基础隔震建筑和大型储油罐，迫切需要采取对策。较少

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