Uncertainty of Identifying Tsunami Deposit based on Various Analyses at the 2011 Tohoku-Oki Tsunami
Abstract
The 2011 Tohoku-oki earthquake triggered various tsunamis in many coastal area from Tohoku to Boso region in northeastern Japan extended over 500 km. Many tsunamis left behind tsunami deposit, mainly composed of sand, which has been studied intensively by many authors so far. Here we collected 2011 Tohoku-oki tsunami deposits from 19 coastal areas from north to south along pacific coast of northeastern Japan and conducted various analyses, such as grain size, diatom species, chemical elements and organic matter in order to evaluate uncertainty of identifying tsunami deposit based on large quantities of data.
We evaluated results of chemical elements and organic matter together with grain size and diatom analysis for the wide range of tsunami deposits formed almost at the same time. We found analytical values of chemical elements varied greatly at each point according to local source of tsunami deposit. For example, Sr, which has been reported to be abundant in tsunami deposit, is rich at some points and vice versa at other areas. The signatures of organic matter determined by C/N ratio and δ13C in particle organic matter in seawater and in most beach sand showed marine origin, and these parameters in soil sample beyond inundated area showed terrestrial origin. Nevertheless, those parameters varied in tsunami deposits. They show marine origin in some areas, while terrestrial origin tend to appear, especially in the inundated area formally covered with woods. These results show that each proxy has uncertainty and thus probabilistic approach is necessary to identify tsunami deposit with high reliability.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMNH41C1020Y
- Keywords:
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- 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDSDE: 4333 Disaster risk analysis and assessment;
- NATURAL HAZARDSDE: 4341 Early warning systems;
- NATURAL HAZARDSDE: 4564 Tsunamis and storm surges;
- OCEANOGRAPHY: PHYSICAL