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Tsunami recurrence revealed by Porites coral boulders in the southern Ryukyu Islands, Japan

Daisuke Araoka, Yusuke Yokoyama, Atsushi Suzuki, Kazuhisa Goto, Kunimasa Miyagi, Keitaro Miyazawa, Hiroyuki Matsuzaki and Hodaka Kawahata
Tsunami recurrence revealed by Porites coral boulders in the southern Ryukyu Islands, Japan
Geology (Boulder) (June 2013) 41 (8): 919-922


Information about past tsunami hazards, such as their recurrence interval and magnitude, is needed for future disaster prediction and mitigation. We examined radiocarbon ages of the surfaces of massive coral boulders cast ashore by past tsunamis in the southern Ryukyu Islands, Japan, where few historical and geological records of past tsunamis are available. We selected only non-eroded Porites coral boulders along the shoreline, because their characteristics make it possible to determine the probable timing of their deposition by tsunamis, and we applied a dating method that uses the cumulative probability distributions of large numbers of radiocarbon measurements of those boulders to determine the timing of past tsunamis. The results demonstrate that the southern Ryukyu Islands have repeatedly experienced tsunami events since at least 2400 yr ago, with a recurrence interval of approximately 150-400 yr. The largest Porites tsunami boulder that we studied (long axis, 9 m), which is probably the largest single-colony tsunami boulder in the world, was displaced by the A.D. 1771 Meiwa tsunami. Although the 1771 Meiwa tsunami was likely the largest event in at least the past 700 yr, calculations of current velocity show that all identified tsunamis occurring before 1771 were probably large enough to cause considerable damage to human-built structures and loss of life. This study demonstrates that by reliably dating large numbers of selected coastal boulders it is possible to ascertain the timing, recurrence interval, and magnitude of past tsunamis in a location where few adequate survey sites of sandy tsunami deposits exist.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 41
Serial Issue: 8
Title: Tsunami recurrence revealed by Porites coral boulders in the southern Ryukyu Islands, Japan
Affiliation: University of Tokyo, Graduate School of Frontier Sciences, Tokyo, Japan
Pages: 919-922
Published: 20130620
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 19
Accession Number: 2013-054383
Categories: Quaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2013256
Illustration Description: illus. incl. sketch map
N24°00'00" - N25°00'00", E124°00'00" - E125°45'00"
Secondary Affiliation: AIST, Geological Survey of Japan, JPN, JapanTohoku University, JPN, JapanJapan Meteorological Agency, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201333
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