Impact of rising sea levels on future Nankai–Tonankai earthquake tsunamis: a case study of Osaka, Japan

ABSTRACT The present study aims to clarify the impact of future sea level rise (SLR) on the anticipated Nankai–Tonankai earthquake tsunami, using Osaka, Japan as the study area. A total of 110 simulations were performed, incorporating 11 tsunami source models, five sea levels and the presence or absence of coastal defences. The simulated results indicated that while maximum nearshore tsunami heights would increase by almost the same magnitude as the rising sea level, changes in the maximum inundation depth, depth-velocity product and momentum flux over land did not reveal simple relationships to sea levels. In addition, if Osaka’s seawalls immediately failed due to the ground shaking transmitted by the earthquake, it was estimated that around 38,000 buildings and 58,000 people would be affected by the tsunami at present (for SLR +0 m), rising to around 120,000 buildings and 150,000 people in the future. In contrast, if they survived the ground shaking, the number of affected buildings and people were shown to be significantly lower, with 7,000 buildings and 18,000 people for SLR +1.0 m. It is thus essential for Osaka to maximise the resilience of the current coastal defence system and property maintain them into the near future.