Provenance of sediments from IODP Expedition 358, (NanTroSEIZE Deep Riser Drilling: Nankai Seismogenic / Slow Slip Megathrust)

IODP 358 探险队的沉积物来源（NanTroSEIZE Deep Riser 钻探：南开地震/慢滑断层）

• 批准号: NE/S016295/1
• 负责人: Kevin Pickering
• 金额: $ 3.21万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FS016295%2F1
• 关键词: Provenance; sediments; IODP; Expedition; 358

Subduction zones, where one plate is forced beneath another, are the locations of the largest-magnitude earthquakes. Typically, these earthquakes occur on faults that are subsea, therefore there is also a hazard due to tsunamis. Recent examples include the Tohoku earthquake in 2011 offshore Japan, in 2004 offshore Sumatra, and in 2016 in southern Chile. Such tsunamigenic earthquakes are caused by slip events along the upper part of the subducting plate in the so-called "seismogenic zone". The material properties of the incoming plate and its sediment cover, referred to as "subduction inputs", play a critical role in the generation of tsunamigenic earthquakes. Therefore, drilling into and instrumenting an active interplate seismogenic zone is a high priority for understanding seismogenic earthquakes.Along SW Japan, the Philippine Sea Plate subducts NW beneath the Eurasian Plate, forming the Nankai subduction zone - one of the best convergent-plate margins to study such zones. The 1944 Tonankai earthquake, the presence of a cluster of a low-frequency seismic events, and the first tectonic tremor recorded in the accretionary prism, show that the area is very active seismically. The NanTroSEIZE is a multi-expedition drilling project built to improve understanding and characterisation of fault architecture, and fault and wall rock composition throughout an active subduction megathrust zone. These expeditions undertaken in the last 10 years, have resulted in >45 holes being drilled in 13 sites, with direct sampling, in-situ measurements, and long-term borehole monitoring data.The IODP Expedition 358 focusses on the deeper part of Site C0002 (Kumano forearc basin) and targets the penetration of the high-amplitude seismic reflector believed to be the main plate boundary fault at ~ 5,000 metres below sea floor (mbsf). Previous expeditions 338 and 348 have already drilled at Site C0002 to 3,058.5 mbsf with casing installed in that hole to 2,922.5 mbsf. These expeditions show that the Kumano forearc basin is mainly infilled by Quaternary deep-marine sediments (e.g., turbidites and hemipelagic muds 1), and that the upper part of the accretionary-prism sediments (~2,000- 3,000 mbsf) are bedded and well-lithified mudstones and sandstones, variably deformed and cemented.Results from previous IODP expeditions (322 & 333) in the Shikoku Basin suggest very oblique subduction (possibly associated with sinistral strike slip) took place during the late Miocene, such that terrigeneous sands may have been supplied to what is now part of the Nankai accretionary prism offshore Honshu-Shikoku from a sediment source in the East China Sea.Lithostratigraphy exerts a first-order influence over the material properties and tectonic behaviour of subduction zones. The 3-D location and proportion of coarse- versus fine-grained sedimentary environments, e.g., submarine channels or lobes, are appreciated among geotechnical engineers and geologists to affect coefficients of friction and permeability of the subduction inputs. This proposed research will contribute to the analysis of the sediment and their provenance in the lower-part of the accretionary prism (>3,000 mbsf), and help in understanding the plate-tectonic evolution of SW Japan, e.g., helping to constrain the hypothesis that oblique subduction associated with sinistral strike slip may have been important the western parts of the late Miocene Nankai subduction system such that early sediment routing to the Nankai system was from the East China Sea.

一个板块被挤压到另一个板块之下的俯冲带，是震级最高的地震发生地。通常，这些地震发生在海底的断层上，因此也有海啸的危险。最近的例子包括2011年日本近海的东北地震，2004年苏门答腊近海的地震，以及2016年智利南部的地震。这种海啸性地震是由所谓的“发震带”中俯冲板块上部的滑动事件引起的。进入板块及其沉积物覆盖层的物质特性，被称为“俯冲输入”，在海啸地震的产生中起着至关重要的作用。因此，对活跃的板块间发震带进行钻探和仪器测量是了解发震地震的首要任务。菲律宾海板块沿日本西南部向北俯冲至欧亚板块之下，形成南开俯冲带，是研究此类俯冲带的最佳板块边缘之一。1944年的托南开地震，出现了一组低频地震事件，并在增生棱镜中记录了第一次构造震动，表明该地区地震非常活跃。NanTroSEIZE是一个多远征钻井项目，旨在提高对整个活动俯冲逆冲带断层结构以及断层和围岩组成的理解和表征。在过去的10年里，这些考察在13个地点钻了45个孔，并进行了直接采样、现场测量和长期钻孔监测数据。IODP远征358集中在站点C0002 （Kumano弧前盆地）的较深部分，目标是在海底以下约5000米（mbsf）的高振幅地震反射器被认为是主要板块边界断层的穿透。之前的338号和348号探险队已经在C0002站点钻探了3058.5 mbsf，并在该井中安装了套管，达到2922.5 mbsf。这些考察表明，熊野弧前盆地主要被第四纪深海沉积物（如浊积岩和半深海泥浆1）所填满，而增生棱镜沉积物的上部（~ 2000 ~ 3000 mbsf）为层状、岩化良好的泥岩和砂岩，变形和胶结程度不一。先前在四国盆地的IODP考察（322和333）的结果表明，晚中新世期间发生了非常斜的俯冲（可能与左旋走滑有关），因此陆源砂可能从东海的沉积物源供应到现在本州-四国近海南开增生棱柱的一部分。岩石地层学对俯冲带的物质性质和构造行为具有一级影响。岩土工程师和地质学家认为，粗粒和细粒沉积环境（如海底通道或叶状）的三维位置和比例会影响摩擦系数和俯冲输入的渗透率。本研究将有助于分析增生棱镜下部（bbb30 000 mbsf）的沉积物及其物源，并有助于了解日本西南部的板块构造演化，例如，有助于限制晚中新世南开俯冲体系西部与左旋走滑相关的斜向俯冲可能起重要作用的假设，因为早期沉积路径来自东海。