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.

我们通过对北海道Yufutsu盆地的s波速度结构和合成地震地面运动进行调查，研究了大地震的长周期地面运动的产生和传播，在2003年的Tokachi-oki地震中，石油从大型储罐中飞溅出来，储罐在火灾中被烧毁，新泻盆地和大都市区。为了确定包括Tomakomai西港在内的Yufutsu盆地沿岸的s波速度结构，我们进行了微震阵列测量。观测到长周期（7秒）运动最大振幅的Tomakomai地震基岩深度比Tomakomai东部和西部都浅。一般认为，长周期地震动与地震基岩深度有关，但低速（Vs ~ 0.8 km/s）的近地表中间层对盆地长周期地震动的放大作用最为显著。我们通过地面运动的二维模拟证实了这一证据。通过2004年kii - hantooki地震和2003年新潟中越地震的地面运动观测对比发现，东京湾地区的长周期地面运动以表面波为主，特别是千叶县沿海地区10秒以上的地面运动较为突出。在新泻盆地进行了横波速度结构调查，指出了长周期运动的意义。得到了盆地中部由7层组成的构造模型。Vs ~ 2 km/s的基底层深度约为5 km。证实了这3个试验点以长周期运动为主，其深层沉积层与长周期运动的增加有较好的相关性。估计这些地区的地面运动表明，对于长期使用的人造建筑物，如基础隔离建筑物和大型储油罐，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