In the Kanto basin, long-period ground motions are often generated by large earthquakes due to the strong amplification of surface waves in thick sediments overlying a rigid basement. Such long-period ground motions cause significant resonance with large-scale constructions such as high-rise buildings and large oil-storage tanks. Thus, it is important to understand the generation properties of long-period ground motions in large basins of populated cities, in order to mitigate and reduce the effects of potential disasters such as from future Nankai Trough earthquakes. The generation and propagation properties of long-period ground motions in central Tokyo from earthquakes at different locations are examined. For this purpose, ground motions generated by the 2004 Mid-Niigata (M 6.8) and the 2011 Fukushima-Hamadori (M 7.0) earthquakes are compared using data obtained by a strong motion network and finite-difference method simulations of seismic wave prop-agation with a heterogeneous subsurface structural model of the Kanto basin. It is shown that radiation of Rayleigh waves from the source and amplification of ground motions in the 3D heterogeneous structure of the Kanto basin produce strong directional variations of the developing strength of long-period ground motions as observed during the Mid-Niigata and Fukushima-Hamadori earthquakes. The results of simulations and their visualized wavefields based on particle motion and wave gradiometry analyses demonstrate the peculiar multi-path and focusing effects of long-period ground motions at central Tokyo interacting with a heterogeneous subsurface structure. Such phenomena are associated with earthquakes occurring north and southwest of Tokyo. On the other hand, such propagation of long-period ground motions do not occur with earthquakes northeastern of Tokyo. These results support weaker long-period ground motions observed in Tokyo during the 2011 Off the Pacific Coast of Tohoku (Mw 9.0) earthquake relative to those of larger and lengthy long-period ground motions developed by the 1944 Tonankai (M 7.9) earthquake.
雑誌名
東京大学地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
93
号
2-4
ページ
31 - 48
発行年
2018
ISSN
00408972
書誌レコードID
AN00162258
著者版フラグ
publisher
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
関東平野における長周期地震動増幅の特徴的方位依存性とその要因
IHO93203_02.pdf
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