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Volume 56 Supplement 3

Special Issue: Special section for the 2003 Tokachi-oki earthquake

Observation of aftershocks of the 2003 Tokachi-Oki earthquake for estimation of local site effects


Observation of aftershocks of the 2003 Tokachi-Oki earthquake was conducted in the southern part of the Tokachi basin in Hokkaido, Japan for estimation of local site effects. We installed accelerographs at 12 sites in Chokubetsu, Toyokoro, and Taiki areas, where large strong motion records were obtained during the main shock at stations of the K-NET and KiK-net. The stations of the aftershock observation are situated with different geological conditions and some of the sites were installed on Pleistocene layers as reference sites. The site amplifications are investigated using spectral ratio of S-waves from the aftershocks. The S-wave amplification factor is dominant at a period of about 1 second at the site near the KiK-net site in Toyokoro. This amplification fits well with calculated 1D amplification of S-wave in alluvial layers with a thickness of 50 meters. In addition to the site effects, we detected nonlinear amplification of the soft soils only during the main shock. The site effects at the strong motion site of the K-NET at Chokubetsu have a dominate peak at a period of 0.4 seconds. This amplification is due to soft soils having a thickness of about 13 meters. Contrary to the results at the two areas, site effects are not significantly different at the stations in the Taiki area, because of similarity on surface geological conditions.


  • Geological Survey of Japan, Digital geological maps of Japan 1:200,000, South Hokkaido, CD-ROM, 2003.

    Google Scholar 

  • Kobayashi, H., Damage of building in southern Hokkaido by earthquake of March 4, 1952, Zisin (Jour. Seism. Soc. Japan), 5, 151157, 1952 (in Japanese with English abstract).

    Google Scholar 

  • Koketsu, K., Y. Yamanaka, K. Hikima, M. Kikuchi, T. Furumura and K. Hatayama, The 2003 Tokachi Oki, Japan, earthquake: Source process and strong ground motions, EOS Trans. AGU, 84(46), Fall Meet. Suppl., Abstract S52L-02, 2003.

    Google Scholar 

  • Matsushima, T., T. Koyanagi, H. Okada, T. Moriya, T. Sasatani, K. Miyakoshi, M. Ikeda, S. Ling, An exploration method using mi-crotremors (7)—Deep geological structures in the Tokachi basin and their effects on seismic motion—, Proceedings of the 85th SEGJ (Society of Exploration Geophysicists of Japan) conference, 264–269, 1991 (in Japanese).

    Google Scholar 

  • Midorikawa, S., Nonlinearity of site amplification during strong ground shaking, Zisin (Jour. Seism. Soc. Japan), 46, 207–216, 1993 (in Japanese with English abstract).

    Google Scholar 

  • The Special Committee for the Investigation of the TOKACHI-Oki Earthquake, Report on the Tokachi-Oki earthquake Hokkaido, Japan, March 1952, pp. 1018, 1954 (in Japanese)

  • Wessel, P. and W. H. F. Smith, Free software helps map and display data, EOS Trans. AGU., 72, 441, 445–446, 1991.

    Google Scholar 

  • Yamanaka, Y. and M. Kikuchi, Source process of the recurrent Tokachi-oki earthquake on September 26, 2003, inferred from teleseismic body waves, Earth Planets Space, 55, e21–e24, 2003.

    Article  Google Scholar 

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Correspondence to Hiroaki Yamanaka.

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Yamanaka, H., Motoki, K., Etoh, K. et al. Observation of aftershocks of the 2003 Tokachi-Oki earthquake for estimation of local site effects. Earth Planet Sp 56, 335–340 (2004).

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