Japan Geoscience Union Meeting 2016

Presentation information


Symbol H (Human Geosciences) » H-CG Complex & General

[H-CG26] Interdisciplinary approach to earth's changing surface

Sun. May 22, 2016 1:45 PM - 3:15 PM 105 (1F)

Convener:*Naofumi Yamaguchi(Center for Water Environment Studies, Ibaraki University), Hajime Naruse(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Koji Seike(Atmosphere and Ocean Research Institute, University of Tokyo), Hideko Takayanagi(Institute of Geology and Paleontology, Graduate School of Science, Tohoku University), Masayuki Ikeda(Shizuoka University), Chair:Naofumi Yamaguchi(Center for Water Environment Studies, Ibaraki University)

2:30 PM - 2:45 PM

[HCG26-04] Sedimentary process of event deposits along the southern Ryukyu forearc and the southern Ryukyu Trench

*Kazuko Usami1, Ken Ikehara1, Toshiya Kanamatsu2, Masayuki Miyazaki2, KanHsi Hsiung2, Taku Ajioka1 (1.Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology, 2.JAMSTEC)

Keywords:earthquake, Ryukyu forearc, Ryukyu Trench , turbidite, subaqueous debris-flow

We conducted piston coring with bathymetric and sub-bottom profiling surveys, along the southern Ryukyu forearc and the southern Ryukyu Trench, for understanding sedimentary process of event deposits in this area. Our final objective is to explore the recurrence record of large tsunami and earthquake archived as deep-sea event deposits along the Ryukyu arc.
Many event deposits considered as turbidites, including many biogenic carbonate-rich very fine-medium sand layers are identified in the piston cores, recovered from a submarine fan located in the southwest of Ishigaki Island. The averaged intervals of the turbidites from two cores recovered from different part of the fan are estimated to be 500–1000 years.
The cores obtained from the forearc basin are intercalated by turbidites including biogenic carbonate-rich very fine-coarse silt, and massive clay layers with gray color almost composed of lithic fragments. The latter sections are possibly originated from the Taiwan region. Lower part of one core recovered from the deepest part of the forearc basin in the south of Ishigaki Island is composed of carbonate-rich very coarse- very fine sand layers considered to be attributed to subaqueous debris-flow. The piston cores obtained from the Ryukyu Trench floor, the coring sites locate behind the natural levee of the channel, are composed of gray silty clay intercalated with numerous coarse silt layers. Most of the coarse layers are <1 cm in thickness.
Araoka, D., Y. Yokoyama, A. Suzuki, K. Goto, K. Miyagi, K. Miyazawa, H. Matsuzaki and H. Kawahata, 2013. Tsunami recurrence revealed by Porites coral boulders in the southern Ryukyu Islands, Japan. Geology 41, 919–922.
Ujiie, H., T. Nakamura, Y. Miyamoto, J.-O. Park, S. Hyun and T. Oyakawa, 1997. Holocene turbidite cores from the southern Ryukyu Trench slope: suggestions of periodic earthquakes. Jour. Geol. Soc. Japan 103, 590–603.