Studies on Evaluation of Long-Period Earthquake Ground Motion Related to Safety Planning of Huge Structures -Evaluation of Long-Period Earthquake Ground Motion for a M8 Hypothetical Kanto Earthquake and Its Problem-

本研究的出发点是确定发生在关东平原附近的8级地震所引起的长周期强地面运动的基本特征。但是，在本研究中途发生的1995年兵库县南部大地震，使我们不得不改变研究计划，对关东平原和大坂盆地的强地震动进行比较。我们对观测到的地震运动进行了评估，调查了地下深部结构，并对两个地区的预期强地震动进行了估计。1995年日本兵库县南部地震时，科比地区的强地面运动具有相当大的破坏力，但其主分量在1 ~ 2秒的周期范围内是相当有限的。当我们讨论更长的周期范围时，关东平原应该比大坂盆地更易弯曲，这是因为以下两个原因。一种可能性是在离关东平原很近的地方发生8级浅源地震。二是平原沉积层在地震运动中会激发出几秒钟的长周期分量。

At the beginning of this study, the objective was to make sure the basic characteristics of long-period strong ground motions due to a M8 earthquake which takes place near the Kanto plain. But the 1995 Hyogoken-Nanbu earthquake, that happened on the halfway of this study, forced to change our research plan to compare the evaluated strong ground motions between the Kanto plain and the Osaka basin.We have made evaluations of observed seismic motions, surveyed underground deep structures, and estimations of expected strong ground motions in both regions.In conclusion, we agreed that the strong ground motion in Kobe area during the 1995 Hyogoken-Nanbu earthquake was big enough for giving heavy damage, but the principal component was quite limited in the period range shorter than one or two seconds. When we discuss the longer period range, the Kanto plain should be more vulnerabkle than the Osaka basin because of the following two reasons. One is the possibility that a M8 shallow earthquake may take place very near from the Kanto plain. The other one is that the sedimentary layrs in the plain will excite long-period components with several seconds in seismic motions.