[M-IS09] [EJ] 津波堆積物

[MIS09-09] Magnetic fabric evidence for rapid, characteristic changes in the dynamics of the 2011 Tohoku-oki tsunami

*Balazs Bradak^1,2、Koichiro Tanigawa³、Masayuki Hyodo^2,4、Yusuke Seto⁴ (1.Research fellow of Japan Society for the Promotion of Science (JSPS)、2.Research Center for Inland Seas, Kobe University, Nada, Kobe, 657-8501, Japan、3.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Site C7 1-1-1 Higashi, Tsukuba 305-8567, Japan、4.Department of Planetology, Kobe University, Nada, Kobe, 657-8501, Japan)

キーワード：magnetic fabric , tsunami dynamics, 2011 Tohoku-oki tsunami

Magnetic fabric (MF) and rock magnetic measurements were applied to sediments deposited by the 2011 Tohoku-oki tsunami to reveal the dynamics of the tsunami run-up and the character of the sedimentation along the Misawa coast, Aomori Prefecture, northern Japan. Two main types of sedimentary environment are described: a higher energy, tangential stress-dominated environment with imbrication and traction/rolling transportation and a calmer, post-peak wave environment ruled by gravitational stress.
Rapid characteristic changes in the tsunami dynamics are also described. The tsunami began with erosion of the pre-tsunami surface caused by rapidly increasing energy. Bedload features such as ripple stratification were developed by the repeated accelerations and decelerations of the tsunami wave during run-up. The arrival of the peak wave was indicated by high-density flow, “slurry-like” sediments. Following the peak wave, the decreasing energy was marked by a change in MF.