Collaborative Research - Sediment pathways, sedimentation processes, and structural growth along the Tohoku segment of the Japan subduction margin: Role of megathrust earthquakes

虽然构造活动、气候、海平面波动和人类活动最常被认为是控制沉积物运移和沉积的重要因素，但地震作为活动边缘沉积物扩散和聚集的因素所起的作用可能被低估。2011年发生在日本海沟的东北地震是本世纪最大的巨型断裂之一。由于日本俯冲系统的仪器特别好，记录了地震前、同震和震后条件的数据前所未有地丰富，这为量化大地震造成的环境变化提供了第一个机会。该项目将结合对2011年地震破裂区域收集的现有沉积岩心和地球物理数据的分析，揭示同震沉积对日本海沟斜坡地层学的贡献。日本海沟是日本一项协调的长期研究计划的重点，这项研究的结果将有助于未来的调查，并加强现有的国际合作。日本同事已经向首席调查员提供了最近获得的地球物理数据，并邀请其中一人参加两次取心巡航。该项目将促进水下古地震学的发展，与陆地古地震学相比，这是一个新兴领域。这项研究的结果将具有高度的社会相关性，因为它们预计将有助于评估日本海沟的地震危险。它们还将适用于其他海沟的地震危险性评估，包括GeoPRISMS的三个重点地点(卡斯卡迪亚海沟、阿留申海沟和新西兰海沟)和波多黎各海沟深处。由于之前获得了NSF的快速拨款，主要调查人员已经开始与日本科学家合作调查2011年的事件。2013年，其中一名首席调查员乘坐R/V Natsushima号参加了两次前往日本海沟的沉积物采样考察。对通过海沟坡度收集的31个活塞岩芯的初步分析表明，其中一些是从2011年事件和之前的事件中采集的沉积物。对多波束测深数据的仔细检查还表明，沿海沟的沉积物特征的变化与小前锋棱柱的形态变化系统地相关，该特征位于海沟下坡，吸收了大部分构造变形。本项目旨在进一步探索这些成果。具体来说，联合分析将解决以下两个问题：--横跨海沟斜坡的大地震的沉积特征是什么？-海底形态和构造结构如何影响同震沉积物的扩散和沉积？通过分析过去地震的沉积记录及其与海底形态和构造结构的关系，该项目将同时对地球科学的两个截然不同的领域做出贡献：活动边缘的同震沉积过程的特征和海底古地震学。

While tectonic activity, climate, sea-level fluctuations, and anthropogenic activity are most often cited as important agents that control sediment transport and depositions, the role of earthquakes as agents of sediment dispersal and accumulation at active margins may be underappreciated. The 2011 Tohoku earthquake at the Japan Trench was one of the largest megathrust ruptures this century. Because the Japanese subduction system is exceptionally well instrumented, an unprecedented wealth of data are accumulating that document pre-seismic, co-seismic, and post-seismic conditions, providing the first opportunity to quantify environmental changes resulting from a megathrust earthquake. This project will integrate the analysis of existing sediment cores and geophysical data collected in the rupture area of the 2011 earthquake to unravel the contributions of coseismic sedimentation to the stratigraphy of the Japan Trench slope. The Japan Trench is the focus of a coordinated, long-term research program in Japan, and results from this study will contribute usefully to future investigations as well as strengthen an existing international collaboration. Japanese colleagues have already provided the Principle Investigators with recently acquired geophysical data and invited one of them to participate in two coring cruises. This project will further the development of underwater paleoseismology, an emerging field compared to land-based paleoseismology. Results from this study will be highly societally relevant as they are expected to contribute to the assessment of seismic hazards at the Japan Trench. They will also be applicable to the assessment of seismic hazards at other oceanic trenches, including three GeoPRISMS's focus sites (Cascadia, Aleutian, and New Zealand trenches) and the deep Puerto Rico Trench.The Principle Investigators have already initiated collaboration with Japanese scientists to investigate the 2011 event, due to a previously funded NSF-RAPID grant. One of the Principle Investigators participated in two sediment sampling expeditions to the Japan Trench in 2013 aboard the R/V NATSUSHIMA. The preliminary analysis of 31 piston cores collected across the trench slope suggests that some of them sampled deposits from the 2011 event and from prior events. Close inspection of multibeam bathymetric data also suggests that variations in sediment characteristics along the trench are systematically correlated with variations in the morphology of the small frontal prism, the feature at the lower trench slope that absorbs most of the tectonic deformation. This project aims to further explore these results. Specifically, the combined analysis will address the following two questions:- What are the sedimentary signatures of great earthquakes across a trench slope?- How do seafloor morphology and tectonic structures affect coseismic sediment dispersal and deposition?By analyzing the sedimentary record of past earthquakes and their relation to seafloor morphology and tectonic structures, this project will contribute simultaneously to two distinct fields of geoscience: the characterization of coseismic sedimentary processes at active margins and submarine paleoseismology.