Tsunami Duration on the South Coast of Shikoku from Large Earthquakes along the Nankai Trough

Sea level fluctuation over 12 hours was recorded on tide gauge in Tosashimizu Bay at the time of the 1944 Showa Tonankai Earthquake tsunami. To clarify the characteristics of tsunami duration on the south coast of Shikoku from Nankai trough earthquakes (which consists of four segments: Tokai, Tonankai, and two Nankai segments), numerical tsunami simulations were carried out. The results showed that two phenomena are responsible for the long duration: shelf seiche of Tosa Bay and edge wave repeatedly propagating between Kitanada Bay and Cape Muroto. Tsunami from Tokai segment generates shelf seiche only, while tsunami from Tonankai and Nankai segments generate both shelf seiche and edge wave.