An Examination on The Tsunami Suffered Risk by Nankai Earthquake for Shrines near Pacific Coast in Shikoku Island

The Pacific coast of Shikoku district facing the Nankai Trough has suffered major tsunami each time due to a trench type earthquake repeated at 100 to 150 years cycle. In the recent Showa-Nankai earthquake occurred in December 1946, there were severe damage such as 1,330 casualties, 11,591 houses in complete destruction, 2599 buildings burned, 2,991 vessels damaged and destroyed. A tsunami hit the coast from Shizuoka prefecture to Kyushu by this earthquake, and a large tsunami exceeding 6 m reached Shirahama, Wakayama Prefecture, Japan.

On the east and west of Shikoku Pacific Coast, Muroto Cape and Ashizuri Cape are extending respectively. In the vicinity of these Peninsula, the tsunami height is expected to increase due to the refraction effect from the topography. Therefore, it is expected there is a high possibility that the damage caused by the tsunami will increase. Damage prediction of the earthquake and tsunami is reviewed on a nationwide scale in response to the 2011 Tohoku Region Pacific Offshore Earthquake. The Cabinet Office forecasts that the probability of the occurrence of the next Nankai Earthquake within 30 years is about 70%.

In previous studies, we conducted a verification of the risk of the tsunami disaster that utilized the assumption result of the Nankai Trough massive earthquake of the Cabinet Office for shrines settled in the coastal 1 km area of ​​Awaji Island and Kii Peninsula. In a series of studies, we regarded the shrine as a temporary evacuation destination in the event of an emergency and limited the coverage to 1 km coastal area. In situations where evacuation can be sufficiently evident, we think that it is appropriate to head to the appropriate evacuation facility.

In this study, we examined the damage risk of the shrine in the shrine within 1km from coasts of Tokushima and Kochi prefectures, which account for most of the coast of the Shikoku region`s Pacific Ocean, and characterized its features.