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-

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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.