Subsurface structure around Fukuoka using borhole data, Japan

Tuesday, 16 December 2014
Naoko Kitada1, Reizi Tanaka1, Naoto Inoue1 and Koichiro Watanabe2, (1)Geo-Research Institute, Osaka, Japan, (2)Kyushu University, Department of Geothechnology, Fukuoka, Japan
Fukuoka is located in the Kyushu area, southwest Japan. In 1999, Fukuokaken Seiho earthquake was occurred and damaged much lifeline and construction. Source fault of this earthquake is the same trend of Kego fault. Kego fault is one of the strike slip fault. This fault activity has a great deal to do with the history of Fukuoka plain. This research is funded by the integrated research project for the Uemachi active fault system in FY2011 by MEXT.

However, detail of Kego fault are not make clear, therefore, from 2011to 2013, the integrated research project for the Kego active fault system by MEXT were carried out. In this project, we are corrected geotechnical borehole data, and make subsurface model for strong motion analysis. Geotechnical borehole data such as preparation of construction are collected over 17000 data. Especially, more than 12000 borehole data were collected in the Fukuoka plain. Although Kego fault is the strike slip fault; we can observe vertical displacement in the plain. Shimoyama et al (2005) were carried out of the geological boring survey along Kego fault at Yakuin area. The result of this study, the maximum vertical displacement of Kego fault in the plain is about 50m at the top of the basement rock. We used these geological information for understanding of geotechnical borehole data.

The result of this study, the displacement of Kego fault on the top of basement rock can recognized from Uminonakamichi to Shimodairi. Subsurface model make each 250m mesh are reproducibly-observed.