5:15 PM - 6:30 PM
[MIS15-P10] Uncertainty of geological information used in identification of tsunami deposit - Preliminary assessment –
Keywords:Tsunami deposit, Identification method, Probabilistic assessment
Tsunami deposit can provide important information about the local history of tsunamis. The geological record of tsunamis has been used to improve hazard maps in coastal cities and to develop the countermeasures against tsunamis in important facilities, such as nuclear power plants. However, the identification of tsunami deposit has uncertainties inherent in geological analysis. To consider the uncertainties in the identification, the authors presented probabilistic identification method for deposit made by natural hazards including tsunami [1]. In this method, deposit with little geological information on its formation is attributed to potential several natural hazards. To utilize this identification method, we must assess the uncertainties of geological information obtained from deposit.
In this study, we assessed the uncertainties of the information obtained from diatom analysis, which is widely used to identify tsunami deposit. We analyzed tsunami deposits formed by the 2011 Tohoku-oki earthquake tsunami [2]. The result showed that the 31% of the tsunami deposit has no marine diatom and more than half of tsunami deposit has marine to brackish diatom (>10% in the total diatom assemblage). The only 8% of the tsunami deposit has no marine to brackish diatom. These results indicate that the fraction of marine to blackish diatom can be the useful proxy to infer the source of deposit. Although choice of better proxy helps reducing uncertainties in geological information inferred from the deposit, we still must take account of the persisting uncertainty on geological information.
[1] Yoshii, T., Tanaka, S., Ito, Y., Hamada, T., Matsuyama, M., Identification method of event deposits caused by natural hazards, JpGU meeting 2019, 2019.
[2] Yoshii, T., Hamada, T., Sasaki, T., Matsuyama, M., Tanaka, S., Ito, Y., Watanabe, M., Okuzawa, K., Sedimentological features of tsunami deposit caused by the 2011 Tohoku-oki earthquake tsunami, JpGU meeting 2014, 2014.
In this study, we assessed the uncertainties of the information obtained from diatom analysis, which is widely used to identify tsunami deposit. We analyzed tsunami deposits formed by the 2011 Tohoku-oki earthquake tsunami [2]. The result showed that the 31% of the tsunami deposit has no marine diatom and more than half of tsunami deposit has marine to brackish diatom (>10% in the total diatom assemblage). The only 8% of the tsunami deposit has no marine to brackish diatom. These results indicate that the fraction of marine to blackish diatom can be the useful proxy to infer the source of deposit. Although choice of better proxy helps reducing uncertainties in geological information inferred from the deposit, we still must take account of the persisting uncertainty on geological information.
[1] Yoshii, T., Tanaka, S., Ito, Y., Hamada, T., Matsuyama, M., Identification method of event deposits caused by natural hazards, JpGU meeting 2019, 2019.
[2] Yoshii, T., Hamada, T., Sasaki, T., Matsuyama, M., Tanaka, S., Ito, Y., Watanabe, M., Okuzawa, K., Sedimentological features of tsunami deposit caused by the 2011 Tohoku-oki earthquake tsunami, JpGU meeting 2014, 2014.