Particle Size Analysis of Japan Trench Sediments from IODP Expedition 386
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Date
2025-05
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The Ohio State University
Abstract
The Japan Trench is a submarine trench located off the northeastern coast of Japan in the North Pacific Ocean. Due to its location on a subduction zone, seismic activity is high, resulting in frequent earthquakes which include the devastating Mw 9.1 Tohoku-Oki earthquake which occurred in 2011. The aftermath of this earthquake revealed the importance of understanding the recurrence interval of massive events within the Japan Trench. The goal of International Ocean Discovery Program (IODP) Expedition 386 is focused on paleoseismic studies of this region. Grain size distributions of 144 ocean sediment samples from depths of ~0.5 – 40 meters below seafloor from Sites M0081F, M0082D, M0083D, M0084F, M0085D, M0086B, M0087D, M0088D, M0090D, M0091D, M0092D, M0093D, and M0095B of IODP Expedition 386 were determined through laser diffraction. A Horiba Partica LA-960V2 Laser Scattering Particle Size Distribution Analyzer, which analyzes how grain size relates to how a particle scatters light, was used to perform this research. For the purposes of this study, most samples are fine-grained muds as sand-rich layers and presumed event-beds were avoided during sample selection. This sample set thus provides background grain size information. The overall mean grain size values show dominance of clayey silts with little, if any, systematic variation with depth at any one site. Average grain size of the near-seafloor sediments increases with proximity to the main canyons along the margin (the Ogawara to the north and the Nakaminato to the south). In the central sites that are farthest from these canyons, mean grain size is smaller.
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Keywords
IODP, Grain Size, Japan Trench, Marine Sediment