日本地球惑星科学連合2018年大会

講演情報

[EE] Eveningポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS04] Nankai Trough Seismogenic Zone Experiment toward the final challenge

2018年5月22日(火) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:金川 久一(千葉大学大学院理学研究科)、Gregory F Moore (University of Hawaii at Manoa)、木下 正高(東京大学地震研究所、共同)、Keir Becker(University of Miami)

[SSS04-P03] Comparison of volcanic glasses from tephra deposits frontal prism and incoming sediments

*福地 里菜1熊 衎昕1Singleton Drake2山口 飛鳥3常 青1木村 純一1長橋 良隆4木村 学5 (1.国立研究開発法人 海洋研究開発機構、2.San Diego State University、3.東京大学、4.福島大学、5.東京海洋大学)

キーワード:テフラ、Core-Log-Seismic Investigation at Sea、南海トラフ

International Ocean Discovery Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), started from 2007, has explored evolutionary processes of deformation and accretion in shallower portion of the Nankai accretionary prism (e.g. Strasser et al; 2009) with understanding the tectonic and sedimentary backgrounds (e.g. Clift et al; 2013; Pickering et al., 2013). The first workshop entitled Core-Log-Seismic Integration at Sea (CLSI@Sea) held in January-February 2018, together with IODP expedition 380 as a part of NanTroSEIZE. The expedition 380 aimed to install a new Long-Term Borehole Monitoring System (LTBMS) in the toe of the Nankai accretionary prism, while the CLSI@Sea reanalyzed the legacy data from the same site acquired during previous expeditions. Lithology group of CLSI@Sea reviewed the previous lithological descriptions and ages including the sites C0006, C0007, C0011, and C0012, of incoming sediments and toe of prism sites to understand the depositional process of slope sediments and development of decollement and the branching thrusts forming the frontal prism.
At Site C0007 of NanTroSEIZE transect in off-Kumano region, present decollement lies in between Pliocene Shikoku Basin facies composed of mudstone and volcanic ash (Unit III) and Pleistocene Trench wedge/Axial channel facies (Unit IV). The sedimentary age of the bottom of Unit III (~5.32 Ma) is equivalent to that of the boundary of Unit IA and IB at C0011, Upper Shikoku Basin sediments. The Upper Shikoku Basin sediments include many tephra layers (e.g. Azuki (0.85 Ma), Pink (1.05 Ma), Habutaki (2.85 Ma), and Ohta (4.0 Ma) ashes). For better age constraint of Site C0007, we determine major and trace element compositions of volcanic glasses included in the tephra layers using LA-ICPMS. In this presentation, we report preliminary results of tephrachlonology and compare the results to that of the input sediments (Site C0011). The results will also be integrated to biostratigraphy, paleomagnetism, and detrital zircon U-Pb dating results (Clift et al., 2013). Updated high-resolution stratigraphic comparison has a potential to reconstruct the faulting/sedimentational history of the prism toe, where very-low-frequency earthquakes and slow-slip events occurs.