5:15 PM - 6:45 PM
[MIS20-P08] the tsunami simulation of ishigaki island
Keywords:Ishigaki Island, tsunami simulation, tsunami deposits
The Meiwa Tsunami was a massive tsunami that occurred on April 24, 1771, in south-southeast of Ishigaki Island, part of the former Ryūkyū kingdom and now part of present-day Okinawa, Japan. This tsunami caused extensive damage to many islands; however, the magnitudes, extents, and slip length of the wave-source fault parameters of the 1771 Meiwa tsunami have not yet been unknown. The Meiwa tsunami wave height was estimated to be up to 30 meters based on how far the tsunami boulders were from the shore. Nakamura (1998) then proposed a model to reconstruct the wave height of the Meiwa tsunami. The tsunami deposits, however, have recently been discovered in the caves on Ishigaki Island. The radiometric ages indicated that most of them were formed about 200 years ago, meaning they were formed when the Meiwa tsunami inundated this region. It should be noted that the ground elevation of some caves reaches up to 40 meters, which is much higher than the previous results of 30 meters, indicating that the previous result of 30 meters may be erroneous. Therefore, in this study, the tsunami simulation model Jagurs was used to reconstruct the 1771 Meiwa tsunami that inundated Ishigaki Island based on the newly reported distribution of the tsunami deposits in the caves. Based on the fault parameters, including the width, length, and slip, were changed, and the calculated tsunami inundation areas were compared with the distribution of the caves where the tsunami deposits were discovered. The current results show that when the wave-source fault was more than 40 km in width, 190 km in length, and 40 m in slip length, the tsunami reached all the caves. In future research, sediment transport modeling will be used to search for tsunami conditions that will allow water and large amounts of coastal sand to reach the caves.