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Identification of 1771 Meiwa Tsunami deposits using a combination of radiocarbon dating and oxygen isotope microprofiling of emerged massive Porites boulders |
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| Authors: | Atsushi Suzuki Yusuke Yokoyama Hironobu Kan Kayo Minoshima Hiroyuki Matsuzaki Nozomu Hamanaka Hodaka Kawahata |
| Institution: | aGeological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba 305-8567, Japan bDepartment of Earth and Planetary Sciences, School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan cInstitute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan dFaculty of Education, Okayama University, Okayama 700-8530, Japan eGraduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan fDepartment of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan gGraduate School of Frontier Sciences, The University of Tokyo, Nakano, Tokyo 164-8639, Japan hOcean Research Institute, The University of Tokyo, Nakano, Tokyo 164-8639, Japan |
| Abstract: | The Meiwa Tsunami, one of the largest tsunamis recorded in historical documents in Japan struck Ishigaki Island and neighboring islands of the Ryukyu Arc in April 1771 AD, killing more than 12 000 people. An enormous number of massive Porites coral boulders are scattered on the shore and in the reef moat of eastern Ishigaki Island. Although these boulders likely were cast ashore by the Meiwa Tsunami, a detailed examination has not yet been conducted. When the marine reservoir effect is taken into account, one of mode values of calibrated radiocarbon dates possibly corresponds to the time of the 1771 event. However, the range of calibrated radiocarbon ages indicates that the transport of the boulders cannot be ascribed solely to the tsunami. Oxygen isotope microprofiling, which indicates sea-surface temperature variation, was therefore conducted to further investigate the mechanism of transport. The results suggest that the skeletal growth of most coral colonies was interrupted in summer or autumn; hence, tropical storms and typhoons are also very likely to be agents of transport. Thus, by combining radiocarbon dating with oxygen isotope microprofiling to investigate Porites coral boulders, it is possible to separate paleotsunami boulders from those transported by storm events as far as tsunamis occurred during the non-storm season. |
| Keywords: | Coral skeleton Oxygen isotope Tsunami Meiwa Tsunami Storm Typhoon Ishigaki Ryukyu |
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