Remobilization of surficial slope sediment triggered by the A.D. 2011 Mw 9 Tohoku-Oki earthquake and tsunami along the Japan Trench

摘要: The A.D. 2011 Tohoku-Oki M w 9 earthquake ruptured the megathrust up to Japan Trench with a large displacement and caused a catastrophic tsunami. This study is first use short-lived radioisotopes, including those emitted by damaged nuclear reactors at the Fukushima Daiichi power plant (Japan), document the remobilization of upper few centimeters sediment as highly significant process triggered its aftershocks. Targeting post-earthquake environment allowed characterization of sedimentary signature this event for better understanding of paleoearthquakes in other tectonically active boundary areas. results stem from 23 piston cores recovered 2013 expedition NT13-19 Agency Marine-Earth Science and Technology. We submarine homogeneous muddy flow deposits that were ground motion 2011. They are highly enriched excess (xs) xs 210 Pb, requiring only centimeters-deep sediment remobilization over areas seafloor. Some contain 134 Cs 137 radioisotopes derived nuclear reactors, indicating sedimentation persisted at least 30 days after main shock. found these deposits all sampling sites in an ∼5000 km 2 area seafloor 4000–6000 m water depth. The study extends ∼260 parallel strike trench. The thickness "Tohoku layer" (3–200 cm) increases toward the zone maximum megathrust slip, where thickest. These results demonstrate shaking above megathrust ruptures near trench remobilized surficial unconsolidated sediment hundreds kilometers. characteristics these deposits may typify resulting fault slips like that of earthquake, but also deposits, contributing their identification record globally.