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Title: 2003年十勝沖地震の最大余震による特異な地震動特性
Other Titles: Anomalous strong ground motion features of the largest aftershock of the 2003 Tokachi-oki earthquake
Authors: 前田, 宜浩1 Browse this author
高井, 伸雄2 Browse this author
笹谷, 努3 Browse this author
Authors(alt): MAEDA, Takahiro1
TAKAI, Nobuo2
SASATANI, Tsutomu3
Issue Date: 19-Mar-2010
Publisher: 北海道大学大学院理学研究院自然史科学部門(地球物理学)
Journal Title: 北海道大学地球物理学研究報告
Journal Title(alt): Geophysical bulletin of Hokkaido University
Volume: 73
Start Page: 217
End Page: 227
Abstract: The largest aftershock(Mw 7.3)of the 2003 Tokachi-oki earthquake(Mw 8.3)generates larger peak ground acceleration(PGA)values than the main shock in the western side of the epicenters despite their magnitude difference. We study the features of strong ground motions from the largest aftershock in detail using PGA values. Spatial distribution maps of PGA ratio between the largest aftershock and adjacent earthquake shows obvious azimuth dependency compared with the other earthquake pairs occurring around Japan. Attenuation relationship of the largest aftershock shows a large azimuth-dependent scattering at distances from 200 to 300 km compared with three smaller earthquakes occurring around the largest aftershock. Because this large scattering appears only in the largest aftershock, we conclude that the azimuth dependency is a peculiar feature of the largest aftershock. Fourier spectral ratios between the largest aftershock and adjacent earthquake at several stations show azimuth dependency at higher frequencies than 1 Hz, which is consistent with the azimuth dependency of PGA values. The azimuth dependency in high-frequency range cannot be explained simply by the source and path effects, and therefore, we make a hypothesis that the azimuth dependency is an apparent one generated by two earthquakes occurring simultaneously at different regions. Synthetic PGA distributions generated by two simultaneous events calculated by the empirical attenuation relationship are in agreement with the observed PGA distribution of the largest aftershock.
Type: bulletin (article)
Appears in Collections:北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University > 第73号

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