Development and Validation of a Tsunami Numerical Model with the Polygonally Nested Grid System and its MPI-Parallelization for Real-Time Tsunami Inundation Forecast on a Regional Scale

We have developed a new numerical model suitable for rapid and wide-area estimation of tsunami inundation and damage. The model is based on the world-renowned TUNAMI code solving the two-dimensional nonlinear shallow water equations, and enables one-stop simulation of the initial tsunami distribution based on a fault model, tsunami propagation and inundation, and damage estimation. It extends the configuration of the grid system from conventional rectangular regions to polygonal regions so that deployment of high-resolution grids can be confined to the coastal lowland, resulting in remarkably improved efficiency in computation and better precision. For the purpose of real-time implementation of tsunami inundation simulation using a high-performance computing infrastructure, vectorization and MPI parallelization have also been conducted. Moreover, the model was verified and validated through several benchmark problems that the National Tsunami Hazard Mitigation Program, organized by federal agencies and states in the U.S., developed as the quality standards for simulating and assessing tsunami hazard and risk. The newly-developed model is named “Real-time Tsunami inundation (RTi) model,” and its computational performance was examined using the SX-ACE, a vector supercomputer installed at Tohoku University. The results show that it requires only 128 cores of the SX-ACE for implementing six-hour tsunami inundation simulation with a 10-meter grid resolution within 10 minutes for the 700 km long coastline of Kochi Prefecture, Japan. This means that the RTi model is over 10 times more efficient as the conventional tsunami model with the rectangular domains, and it can be inferred that 2,451 cores of the SX-ACE are the overall computational resources needed for real-time tsunami inundation forecast on the whole coastal regions along the Nankai Trough subduction zone, corresponding to the computational performance of 170 Tflop/s. The resources required are equivalent to 24% of all the SX-ACE resources at Tohoku University, indicating the feasibility of real-time tsunami inundation forecast on a regional scale by using the RTi model. Since the Disaster Information System operated by the Cabinet Office of the Japanese Government adopted a function of tsunami damage estimation using the aforementioned numerical model, at the end of this paper, a brief overview of the subsystem for rapidly estimating tsunami damage on a regional scale is described.