2018 Fiscal Year Final Research Report
Cosmogenic nuclide dating to determine timings of huge tsunami using boulders derived from a dike of quartz porphyry in Hashigui-iwa facing the Nankai Trough, Pacific side of central Japan
| Project/Area Number |
16K01223
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Geography
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| Research Institution | Hosei University |
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Principal Investigator |
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| Research Collaborator |
SHISHIKURA Masanobu
NAMEGAYA Yuichi
ECHIGO Tomoo
YOKOYAMA Yusuke
MIYAIRI Yosuke
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | 南海トラフ / 南海地震 / 巨大津波 / 宇宙線照射年代 / 津波漂礫 |
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| Outline of Final Research Achievements |
We carried out field surveys at Hashigui-iwa in October 2014 to take rock samples from the surface of the boulders for cosmogenic nuclide dating. We also took some samples from volcanic dike itself to compare ages with those of the boulders. We used electric disk grinder with diamond blade to take off rock surfaces thinly less than two centimeters in thickness. We took rock samples more than ten kilograms at each place because expected age must have been younger than a few thousand years BP. We finally took six samples for cosmogenic nuclide dating there.Cosmogenic nuclide dating can be used to determine timing of huge tsunamis. We supposed to use beryillium-10 which occur in minerals in rocks, such as quartz, however, could not determine the cosmogenic dates due to a serious dating machine trouble. The result of tsunami ages was reported using alternative dating method such as radio carbon dating at the AGU the Fall Meeting 2018.
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| Free Research Field |
自然地理学
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| Academic Significance and Societal Importance of the Research Achievements |
南海地震に伴う津波は、東日本大震災以来社会的に注目されており、被害想定など国をあげて取り組んでいる。本研究は南海地震が近海で頻発してきた紀伊半島南端部の串本町において、海岸の岩棚上に散らばっている巨礫に注目し、それらの巨礫を運搬した力は過去の大津波であると推定し、その発生年代について、宇宙線照射年代測定法を用いて求めようとした。結果的には機器のトラブルで研究期間内に結論は出なかったが、もし過去の大津波の発生年代や間隔がわかれば、津波災害の減災に役立ち、社会的意義は大きいと考えられる。また、津波堆積物を直接宇宙線照射年代測定した研究はまだほとんどなく、学術的にも挑戦的な研究だと考えている。
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