[S-SS13] Strong Ground Motion and Earthquake Disaster

[SSS13-P11] Estimation of Site Amplification Characteristics in Kumamoto plain by Spectral Separation Analysis Using Aftershock Records of the 2016 Kumamoto Earthquake

*Tomomi Iida¹, Hiroaki Yamanaka¹, Kosuke Chimoto¹, Daiki Shinoyama⁸, Seiji Tsuno⁵, Masahiro Korenaga⁵, Nobuyuki Yamada⁷, Hiroe Miyake⁶, Tatsuo Kanno³, Michiko Shigefuji³, Masayuki Yoshimi², Shinichi Matsushima⁴, Hiroshi Kawase⁴, Kimiyuki Asano⁴, Tomotaka Iwata⁴ (1.Tokyo institute of Technology, 2.National Institute of Advanced Industrial Science and Technology, 3.Kyushu University, 4.Kyoto University, 5.Railway Technical Research Institute, 6.The University of Tokyo, 7.Kochi Unicersity, 8.Central Research Institute of Electric Power Industry)

Keywords:Spectral inversion technique, the 2016 Kumamoto Earthquake, Site Amplification

The 2016 Kumamoto earthquake contains a foreshock with an Mj of 6.5 on April 14 and the main shock with an Mj of 7.3 on April 16. The earthquakes generated ground motions with a seismic intensity of 7 on the Japan Meteorological Agency scale twice in Mashiki, Kumamoto, Japan and many wooden houses were collapsed. In this study we estimated site amplification characteristics in Kumamoto plain by using ground motion records at strong motion stations of K-NET, KiK-net, seismic intensity-meters stations by local governments and aftershock observation stations by Yamanaka et al. (2016) through a spectral inversion technique. We choose the OITH08 station as the referential site in the inversion. The estimated frequency dependent Q and the source characteristics by the spectral inversion technique show similar features to those from previous studies (e.g. Somei et al, 2018). The site amplifications in the alluvium plain show large values in a frequency range of 0.5-2.0Hz. At high frequency the site amplifications of the mountain are larger than those of the plain area. We estimated S-wave velocity structures in Kumamoto plain by an inverse analysis of the site amplifications. The sediments are large in central area of the Kumamoto plain.
Acknowledgements: This work was conducted as a part of the Comprehensive Study on the Futagawa-Hinagu fault zone after the 2016 Kumamoto earthquake, MEXT.