Japan Geoscience Union Meeting 2015

Presentation information

International Session (Poster)

Symbol S (Solid Earth Sciences) » S-SS Seismology

[S-SS02] Frontier studies on subduction zone megathrust earthquakes and tsunamis

Mon. May 25, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Kyuichi Kanagawa(Graduate School of Science, Chiba University), Demian Saffer(Dept. of Geosciences, The Pennsylvania State University, USA), Michael Strasser(Geological Institute, Seiss Federal Insitute of Technology ETH Zurich), Yasuhiro Yamada(Depertment of Urban Management Engineering, Kyoto University), Shuichi Kodaira(Institute for Research on Earth Evolution Japan Agency for Marine-Earth Science and Technology), Ryota Hino(International Research Institute of Disaster Science, Tohoku University), Kohtaro Ujiie(Graduate School of Life and Environmental Sciences, University of Tsukuba), Yoshihiro Ito(Disaster Prevention Research Institute, Kyoto University)

6:15 PM - 7:30 PM

[SSS02-P08] Incoming materials for an erosional subduction zone, offshore Osa Peninsula, Costa Rica

*Jun KAMEDA1, Robert HARRIS2, Mayuko SHIMIZU3, Kohtaro UJIIE4, Akito TSUTSUMI5, Minoru IKEHARA6, Masaoki UNO7, Asuka YAMAGUCHI8, Yohei HAMADA9, Yuka NAMIKI5, Gaku KIMURA10 (1.Hokkaido University, 2.Oregon State University, 3.Japan Atomic Energy Agency, 4.University of Tsukuba, 5.Kyoto University, 6.Kochi University, 7.Tohoku University, 8.Univeristy of Tokyo, 9.Japan Agency for Marine-Earth Science and Technology, 10.University of Tokyo)

Bulk mineral assemblages of sediments and igneous basement rocks on the incoming Cocos Plate at the Costa Rica subduction zone were examined by X-ray diffraction (XRD) analyses on core samples. These samples are from Integrated Ocean Drilling Program (IODP) Exp. 334 reference Site U1381, ~ 5 km seaward of the trench, cored as part of the Costa Rica Seismogenesis Project (CRISP).
Drilling recovered approximately 100 m of sediment and 70 m of igneous oceanic basement. The sediment includes two lithologic units: hemipelagic clayey mud (unit 1) and siliceous to calcareous pelagic ooze (unit 2). The hemipelagic unit is composed of clay minerals (~50 wt.%), quartz (~5 wt.%), plagioclase (~5 wt.%), calcite (~15 wt.%) and ~30 wt.% of amorphous materials, while the pelagic unit is mostly made up of biogenic amorphous silica (~50 wt.%) and calcite (~50 wt.%). The igneous basement rock is composed of plagioclase (~50-60 wt.%), clinopyroxene (~>25 wt.%), and saponite (~15-40 wt.%). Saponite is more abundant in pillow basalt than in the massive section, reflecting the variable intensity of alteration. Fluid expulsion models shows that sediment compaction during shallow subduction causes the release of pore water while peak mineral dehydration occurs at temperatures of approximately ~100℃. The subducting sediment has the potential to generate fluid overpressure at distances of between 5 and 70 km landward of the trench.