11:00 〜 13:00
[HDS10-P11] 1771年明和津波の波源の再検討と人的被害評価
キーワード：古津波、津波数値計算、人的被害
The 1771 Meiwa tsunami caused great human suffering (about 12,000 people) along the Sakishima Islands, located in the southern part of the Ryukyu Islands, Japan. Based on historical and geological records of this tsunami, various source models have been proposed. However, the tsunami source has been controversial and high-resolution inundation modeling is required for proper evaluation. It is also important to integrate recent geological and historical results such as the fact that 1) tsunami occurred at periodic intervals of several hundred years (Araoka et al., 2013; Ando et al., 2018), and 2) there was evidence of strong ground tremor in Ishigaki Island (Yamamoto, 2008).
In this study, we re-examined the source of the Meiwa tsunami by conducting high-resolution inundation modeling to investigate the appropriate source model. We further evaluated human casualties of the Meiwa tsunami to contribute to the future regional disaster prevention.
As a result of the parameter study of tsunami source models, we found that an extremely large slip amount was required compared to the earthquakes observed so far, if only trench-type earthquake was assumed. Based on these results, we concluded that it would be more realistic to consider additional tsunami source(s). Okamura et al. (2018) reported huge submarine landslide near the trench axis and its location is close to the zone where extremely large slip was required to explain the tsunami inundation at southern part of Ishigaki Island. Therefore, the Meiwa tsunami may have been generated not only by a trench-type earthquake, but submarine landslide(s) might have been triggered by the earthquake and enhanced the tsunami size.
The mortality rate in relation to the flow depth of the Meiwa tsunami was higher than that of the 2011 off the Pacific coast of Tohoku earthquake tsunami at Sendai and Sanriku regions, but rather similar to that of the 2004 Indian Ocean tsunami at Banda Aceh City in Indonesia. The huge human suffering caused by the Indian Ocean tsunami is explained to be the lack of tsunami preparedness and tsunami awareness among the local people, because the predecessor was occurred about 600 years ago (Suppasri et al., 2016). The tsunami recurrence interval at Sakishima Islands is also estimated to be long about few hundred years in the recent studies (Ando et al., 2018; Fujita et al., 2020). Therefore, the situation of the Meiwa tsunami is thought to have been similar to that of the Indian Ocean tsunami.
In this study, we re-examined the source of the Meiwa tsunami by conducting high-resolution inundation modeling to investigate the appropriate source model. We further evaluated human casualties of the Meiwa tsunami to contribute to the future regional disaster prevention.
As a result of the parameter study of tsunami source models, we found that an extremely large slip amount was required compared to the earthquakes observed so far, if only trench-type earthquake was assumed. Based on these results, we concluded that it would be more realistic to consider additional tsunami source(s). Okamura et al. (2018) reported huge submarine landslide near the trench axis and its location is close to the zone where extremely large slip was required to explain the tsunami inundation at southern part of Ishigaki Island. Therefore, the Meiwa tsunami may have been generated not only by a trench-type earthquake, but submarine landslide(s) might have been triggered by the earthquake and enhanced the tsunami size.
The mortality rate in relation to the flow depth of the Meiwa tsunami was higher than that of the 2011 off the Pacific coast of Tohoku earthquake tsunami at Sendai and Sanriku regions, but rather similar to that of the 2004 Indian Ocean tsunami at Banda Aceh City in Indonesia. The huge human suffering caused by the Indian Ocean tsunami is explained to be the lack of tsunami preparedness and tsunami awareness among the local people, because the predecessor was occurred about 600 years ago (Suppasri et al., 2016). The tsunami recurrence interval at Sakishima Islands is also estimated to be long about few hundred years in the recent studies (Ando et al., 2018; Fujita et al., 2020). Therefore, the situation of the Meiwa tsunami is thought to have been similar to that of the Indian Ocean tsunami.