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[HCG26-04] Sedimentary process of event deposits along the southern Ryukyu forearc and the southern Ryukyu Trench
Keywords:earthquake, Ryukyu forearc, Ryukyu Trench , turbidite, subaqueous debris-flow
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.