17:15 〜 18:30
[MIS15-P09] Comparison of Observations and Numerical Simulations of Sediment Transport Using the 1707 CE Hoei Tsunami Source Model: Application to Kanigaike Pond in Kochi Prefecture, Japan
キーワード：1707年宝永地震、津波堆積物、津波土砂移動
The Nankai Trough subduction zone have repeatedly produced large earthquakes with tsunamis (e.g., Ando, 1975; Ishibashi, 2004). The 1707 CE Hoei Nankai earthquake and tsunami caused serious damages to the southwestern coast of Japan. Its damages have been described many historical documents and its tsunami deposits have been found from the coastal lowlands from Kyusyu to Tokai (e.g., Cabinet Office, 2011; Kitamura and Kobayashi, 2014). Therefore, it is considered that the 1707 CE Hoei earthquake was a M9-class event on the Nankai Trough subduction zone. The source models have been proposed based on its tsunami heights and its tsunami deposits (e.g., Furumura et al., 2011; Sugawara et al., 2019). However, they are still not enough. In this study, we examine the sedimentary process of the tsunami deposits from the comparison of observation and numerical simulation of tsunami sediment transport using the revised 1707 CE Hoei tsunami source model (Furumura et al., 2011).
Study site is a coastal pond (Kanigaike pond) in Kochi Prefecture, Japan. The sand movements were computed using a coupled numerical model of tsunami inundation and sediment transport developed by Takahashi et al. (1999). The saturation concentration of suspended sediments.was also adopted (e.g., Sugawara et al., 2014; Yamashita et al., 2016). The mean grain size of the sand was set to be 0.267 mm and grain-size dependent parameters (i.e., the coefficients of bedload rate and exchange rate, settling velocity, and critical shear stress) were provided by Takahashi et al. (2011).
Our results showed a sand deposition of ~1 m near the shoreline. However, few sand deposition took place in the pond. According to the tsunami deposit survey performed by Kochi University and Okamura and Matsuura (2012), the 1707 CE Hoei tsunami deposits were ~50 cm in thickness. Our results did not match the observations, suggesting the need of reevaluation with different slip amount and width of the subfaults.
We concluded that the 1707 CE Hoei tsunami source model should be reexamined based on geological evidences, although there are several uncertainties in tsunami sediment transport modeling (Jaffe et al., 2016; i.e., incompleteness of the theory, topographic and bathymetric changes, parameter setting). Further studies would lead to further understanding of the Nankai Trough megathrust earthquakes.
Study site is a coastal pond (Kanigaike pond) in Kochi Prefecture, Japan. The sand movements were computed using a coupled numerical model of tsunami inundation and sediment transport developed by Takahashi et al. (1999). The saturation concentration of suspended sediments.was also adopted (e.g., Sugawara et al., 2014; Yamashita et al., 2016). The mean grain size of the sand was set to be 0.267 mm and grain-size dependent parameters (i.e., the coefficients of bedload rate and exchange rate, settling velocity, and critical shear stress) were provided by Takahashi et al. (2011).
Our results showed a sand deposition of ~1 m near the shoreline. However, few sand deposition took place in the pond. According to the tsunami deposit survey performed by Kochi University and Okamura and Matsuura (2012), the 1707 CE Hoei tsunami deposits were ~50 cm in thickness. Our results did not match the observations, suggesting the need of reevaluation with different slip amount and width of the subfaults.
We concluded that the 1707 CE Hoei tsunami source model should be reexamined based on geological evidences, although there are several uncertainties in tsunami sediment transport modeling (Jaffe et al., 2016; i.e., incompleteness of the theory, topographic and bathymetric changes, parameter setting). Further studies would lead to further understanding of the Nankai Trough megathrust earthquakes.