著者

古村 孝志 武村 俊介 早川 俊彦

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.3, pp.576-587, 2007-08-25

参考文献数

15

被引用文献数

5 9

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Large and prolonged shaking with long-period ground motions having periods of about 7 sec were observed in central Tokyo during the Off Niigata-ken Chuetsu, Japan, M6.8 earthquake on 16 July, 2007. The observed ground motions from a dense nationwide strong motion network (KNET and KiK-net) demonstrate clearly that the long-period ground motions consist of Rayleigh waves, which developed at the northern edge of the Kanto Basin and were induced by conversion from the S waves radiating from the earthquake source. The amplitude and the duration of the long-period surface waves were enhanced dramatically as they propagated in the Kanto Basin, which has a thick cover of sedimentary rocks overlaying rigid bedrock. Observed ground motions of long-period signals at the center of Tokyo from the 2007 Off Niigata-ken Chuetsu event correlated well with observations from the Chuetsu earthquake on 23 Oct. 2004 (<I>M</I> 6.8). By analyzing waveform data from the main shock and aftershocks of the 2007 Off Niigata-ken Chuetsu earthquake and the Chuetsu earthquake in 2004, it is found that the long-period surface wave having a dominant period of about 7 sec at the center of Tokyo is developed efficiently by a large earthquake with a magnitude greater than about M6.5-7, but it is not developed by small earthquakes of less than about <I>M</I>6.5.