*Takatoshi Yanagisawa¹, Megumi Akashi², Yuji Tasaka³, Ataru Sakuraba⁴ (1.Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 2.Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf, 3.Faculty of Engineering, Hokkaido University, 4.School of Science, The University of Tokyo)