HR: 0800h
AN: OS31A-0159    [Abstracts]
TI: Aperiodic recurrence of Holocene tsunamis in eastern Hokkaido, Japan
AU: * Sawai, Y
EM: yuki.sawai@aist.go.jp
AF: Geological Survey of Japan, AIST, Site C7 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Kamataki, T
EM: kamataki-takanob@oyonet.oyo.co.jp
AF: OYO Corporation, Daitakubo 2-2-19, Minami-ku, Saitama, 336-0015, Japan
AU: Shishikura, M
EM: m.shishikura@aist.go.jp
AF: Geological Survey of Japan, AIST, Site C7 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Nasu, H
EM: nasu_hiroo@soken.ac.jp
AF: The Graduate University for Advanced Studies, Shonan Village, Hayama, 240-0193, Japan
AU: Okamura, Y
EM: okamura-y@aist.go.jp
AF: Geological Survey of Japan, AIST, Site C7 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Satake, K
EM: kenji.satake@aist.go.jp
AF: Geological Survey of Japan, AIST, Site C7 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Thomson, K H
EM: K.H.THOMSON@durham.ac.uk
AF: Durham University, South Road, Durham, DH1 3LE, United Kingdom
AU: Matsumoto, D
EM: dandan@kueps.kyoto-u.ac.jp
AU: Yamaguchi, M
EM: masaaki.yamaguchi@aist.go.jp
AF: Geological Survey of Japan, AIST, Site C7 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Fujii, Y
EM: fujii@kenken.go.jp
AF: Building Research Institute, 1 Tatehara, Tsukuba, 305-0802, Japan
AU: Komatsubara, J
EM: j.komatsubara@aist.go.jp
AF: Geological Survey of Japan, AIST, Site C7 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Aung, T T
EM: aung-than@aist.go.jp
AF: Geological Survey of Japan, AIST, Site C7 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AB: Sandy deposits provide evidence for 15 tsunamis between 200 and 6,000 years ago at a muddy lagoon (Mochirippu) and a peaty beach-ridge plain (Kiritappu) 15 km apart along the Pacific coast of eastern Hokkaido. Additional sand beds at the lagoon probably represent historical tsunamis of A.D. 1843 and 1894. We observed the sequences of sandy deposits in continuous slices 2-4 m deep. Some of the deposits consist of just a single sand bed, while others contain multiple units of sand, mud, and plant detritus. We bracketed the ages of most the inferred tsunamis by a historical tephra (B-Tm: AD 947) and AMS radiocarbon dating of detritus from pre- and post-tsunami beds of mud and peat. The main materials dated are seeds and leaves at the lagoon and charcoal from the beach-ridge plain. Tsunami dates computed from the bracketing ages commonly have uncertainties, at two standard deviations, that span two to four sidereal centuries. Within these uncertainties the inferred sequence of 15 prehistoric tsunamis at the lagoon, beginning almost 6,000 years ago, can be matched tsunami by tsunami with the inferred history at the beach-ridge plain 15 km away. The intervals between the inferred tsunamis average nearly 400 years and range from as little as a century to as much as a millennium.
DE: 1115 Radioisotope geochronology
DE: 1145 Tephrochronology (8455)
DE: 4564 Tsunamis and storm surges
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting