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

DESCRIPTION: 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: (1) What are the sedimentary signatures of great earthquakes across a trench slope? (2) 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.