10:00 AM - 10:15 AM
[MIS33-05] Spatial extent of sedimentation triggered by the 2011 Tohoku earthquake from short-lived radioisotope data, Japan Trench
Keywords:Sedimentation generated by Tohoku 2011 earthquake, spatial distribution and pulses of sedimentation, short lived radioisotopes track sedimentation, Mid-slope terrace, Japan Trench, detection of Fukushima signature in sediments, sedimentation relative to maximum megathrust slip
Very high activities in xs210Pb and concentrations of 137Cs were measured in the upper half-meter of the cores. Detection of 134Cs and enrichment of 137Cs provided a Fukushima signature that was found in the upper 15 cm of several cores. Together with x-ray fluorescence elemental analyses, these radioisotopes provide evidence for multiple pluses of sedimentation triggered by the Tohoku 2011 earthquake and possibly some of its aftershocks, and of older earthquakes that occurred as far back as the last hundred years.
Widespread shaking by the 2011 earthquake induced synchronous fluidization and resuspension of near bottom sediments for ~250 km along the strike of the Japan Trench. Sediment thickness seems to depend on its proximity to the zone of maximum megathrust slip, but could also depend on local topography and supply of unstable sediment. The sediment deposited as a result of the earthquake shaking is homogeneous and lacks bioturbation. The earthquake also generated turbidity currents as evidenced by sand-rich beds. Proximal to the area of maximum megathrust slip, and presumably disruption on the upper plate, the earthquake caused brecciation, dewatering and minor slumping of sediments. Re-suspended sediments were deposited on the seafloor for at least 30 days after the earthquake and likely for much longer.