In this study, tsunami simulations are conducted by assuming an M8.5 earthquake generated along the Tonga Trench, including horizontal deformation effect, and using a depth of five kilometers aligned to the buried faults. We performed numerical tsunami simulations using the Tohoku University's Numerical Analysis Model for Investigation (TUNAMI) code for the linear or non-linear wave equations in a spherical coordinate system. We tested two bathymetry data of GEBCO and ETOPO for single grid computations. We used the GEBCO for bathymetry data and the SRTM data for the topography for the tsunami inundation simulations. We adopted the nesting grid system with four layers including the finer grid merging the GEBCO and SRTM data on the tsunami inundation area. We selected two study areas to focus on the inundation: Suva and Ono-i-Lau. We placed four output points along the Suva coastlines in FDB foreshore, Walu bay, Lami, and Draunibota. The computational result in the Suva study area shows that the maximum inundation height recorded was at Walu Bay, with a height of 3.06 meters, and the earliest wave recorded was at FDB foreshore, with a time of 103.8 minutes. For the second study area in Ono-i-Lau, the four output points are Nukuni, South Nukuni, North Matokana, and Doi. The results show that the maximum inundation height recorded was at South Nukuni, with a height of 1.61 meters, and the earliest wave recorded was also at South Nukuni, with a time of 62.5 minutes.
Keywords: Tonga Trench, Horizontal deformation effect, Buried faults, Tsunami inundation, Tsunami simulations.