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-

在这项研究的开始，目的是确定关东平原附近发生的8级地震引起的长周期强地面运动的基本特征。但是，1995年发生在本研究中途的神户-南方地震迫使我们改变了研究计划，将关东平原和大阪盆地之间评估的强地面运动进行了比较。我们对这两个地区的观测地震运动、地下深部结构进行了评估，并对预期的强地面运动进行了估计。最后，我们一致认为，1995年日本地震期间神户地区的强地面运动足以造成严重破坏，但主分量相当有限，在一到两秒的周期范围内。当我们讨论更长的周期范围时，关东平原应该比大阪盆地更脆弱，原因有两个。其一，关东平原附近有可能发生8级浅层地震。另一种是平原上的沉积层在地震运动中激发出数秒的长周期分量。

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.