Numerical simulation of the impacts of reflected tsunami waves on Pulo Raya Island during the 2004 Indian Ocean tsunami

The island is part of the Aceh Jaya district in Aceh Province, Indonesia. Prior to the 2004 Indian Ocean tsunami, Pulo Raya had three villages: Lhok Siron, Lhok Meu, and Ujung Manek, with a population of about 363 people. The tsunami waves destroyed many of the island's facilities, including a mosque, a school, and houses. The study investigates the hydrodynamic processes of reflected tsunami waves and their impact on Pulo Raya Island using a Cornell Multi-grid COupled Tsunami (COMCOT) model. The simulation confirms eyewitness accounts that it was not the initial runup, but the reflected waves that devastated the worst-hit areas of the island. The results provide basic information about the potential for reflected tsunami waves to destroy the lee side of coastal areas and serve to warn community members and governments of the need for further preparation for and awareness about damage on the lee sides of small islands during tsunami disasters. The COMCOT model, which consists of two Shallow Water Equations (SWEs), namely the Linear (LSWE) and Nonlinear (NLSWE), with a leap-frog explicit finite difference method, was used to simulate the tsunami wave runup and subsequent hydrodynamic processes. The NLSWE formulated in COMCOT is used in shallow conditions to solve convective inertia force and bottom friction terms. The model parameters and input data adopted in this research are elucidated as follows. The rupture area after the shock of the 2004 Indian Ocean earthquake extended about 1200 km from the epicenter in the western area of Aceh Province to Andaman Island. Based on the Global CMT catalog, the earthquake was indicated as thrust type faulting with focal mechanism namely strike, slip, dip about 329, 8, and 110, respectively. The rupture process was complex, and a multi-fault model was proposed to represent this event. The fault model was used to simulate the tsunami wave propagation and inundation at coastal areas. The numerical simulation of the impacts of reflected tsunami waves on Pulo Raya Island was conducted using the COMCOT model. The simulation results show that the reflected tsunami waves were amplified around the lee side of the island, resulting in a higher runup and more severe damage to the coastal areas. The results of this study provide valuable information for tsunami mitigation and preparedness on small islands, particularly in Indonesia, where many small islands are populated and vulnerable to tsunami disasters. The study area, Pulo Raya Island, is located in a region prone to tsunami disasters, and the results of this study highlight the importance of considering the impacts of reflected tsunami waves on small islands. The study's findings can be used to inform tsunami mitigation and preparedness strategies, including the development of early warning systems, evacuation plans, and infrastructure design. The results also emphasize the need for further research on tsunami dynamics and the development of more accurate models for simulating tsunami wave propagation and inundation.