[M-GI28] 地球掘削科学

[MGI28-P01] Holocene–Upper Pleistocene event deposit stratigraphy along the Japan Trench: Initial results from IODP Expedition 386 “Japan Trench Paleoseismology”

*池原 研¹、Strasser Michael²、板木 拓也¹、里口 保文³、長橋 良隆⁴、金松 敏也⁵、石澤 尭史⁶、Huang Jyh-Jaan⁷、Everest Jeremy⁸、前田 玲奈⁵、IODP Expedition 386 Science Party (1.産業技術総合研究所地質情報研究部門、2.インスブルック大学、3.琵琶湖博物館、4.福島大学、5.海洋研究開発機構、6.東北大学、7.国立台湾大学、8.英国地質調査所)

キーワード：地震履歴、タービダイト、日本海溝、IODP

Hadal oceanic trenches are the deepest places on our planet. They act as terminal sinks for sediment and particulate and dissolved organic carbon, and form high-resolution archives to unravel the history of subduction zone processes including the giant earthquakes that occur along the trench. Short historical and even shorter instrumental records limit our perspective of earthquake maximum magnitude and recurrence, and thus are inadequate to fully characterize Earth’s complex and multiscale seismic behavior and its consequences. Motivated by the mission to fill the gap in long-term paleoseismic records of giant (Mw 9 class) subduction zone earthquakes, such as the Tohoku-Oki earthquake in 2011, International Ocean Discovery Program (IODP) Expedition 386 successfully collected 29 Giant Piston cores at 15 sites (total core recovery 831.19 meters), recovering up to 37.82-meter-long, continuous, upper Pleistocene to Holocene stratigraphic successions of 11 individual trench-fill basins that are expected to have recorded past earthquakes. Preliminary expedition results document event-stratigraphic successions comprising numerous event deposits and initially characterize their different types, facies, properties, composition and frequency of occurrence, which show spatial variations along the Japan Trench. The occurrence of several tephra beds, radiolarian biostratigraphic events and characteristic paleomagnetic secular variations reveals high potential for establishing robust age-models in the Holocene to Upper Pleistocene sequence. In the central Japan Trench, our initial results reveal (1) good correlation of the three marker event beds in the uppermost stratigraphic intervals with the established paleoseismic record of the last 1500 years, (2) good correlation of older thick event deposits with the predicted event-stratigraphy from high-resolution sub-bottom profiles, (3) occurrence of several tens older thick event deposits comprising similar characteristics as event deposits from major historical earthquakes, and (4) no major differences in general sedimentary facies and lithostratigraphy between Holocene and Upper Pleistocene sequences, suggesting that little influence of eustatic sea-level changes for formation of event deposits. Our ~24 kyr paleoseismic record in the central Japan Trench enables new perspectives for the discussion on long-term recurrence patterns of megathrust earthquakes.

IODP Expedition 386 Science Party: Piero Bellanova; Morgane Brunet; Zhirong Cai; Antonio Cattaneo; Katharina Hochmuth; Kanhsi Hsiung; Takashi Ishizawa; Takuya Itaki; Kana Jitsuno; Joel Johnson; Toshiya Kanamatsu; Myra Keep; Arata Kioka; Martin Kölling; Christian Maerz; Cecilia McHugh; Aaron Micallef; Luo Min; Dhananjai Pandey; Jean Noel Proust; Troy Rasbury; Natascha Riedinger; Rui Bao; Yasufumi Satoguchi; Derek Sawyer; Chloe Seibert; Maxwell Silver; Susanne Straub; Joonas Virtasalo; Yonghong Wang; Ting-Wei Wu; Sarah Zellers