How will we cope if several Southeast Asian ports close for more than 200 days because of a tsunami? This is one of the questions we should be ready to answer if we want to be ready for a major earthquake striking in the Manila Trench of the South China Sea – one that many call the Big One. It doesn’t even need to be the Big One for tsunamis to severely impact communities. Recent tsunamis, such as those generated by earthquakes in Kamchatka in July 2025 and offshore Mindanao in the Philippines in October 2025, attracted significant attention, prompted evacuations and raised questions about whether the tsunami risk might be changing in the region.
“For Singapore, our current models forecast tsunami waves that are generally less than one-metre high, so the tsunami hazard remains low,” said Professor Adam Switzer from the Asian School of the Environment and Earth Observatory of Singapore (EOS) at Nanyang Technological University Singapore. “Tsunamis in Singapore would likely lead to minimal coastal flooding, but they could generate strong currents which is vastly understudied.” In these models, such tsunamis would be coming from offshore the Philippines, where a major underwater fault called the Manila Trench can generate earthquakes of magnitude-8 and above.
Professor Adam Switzer explaining the tsunami hazard in Southeast Asia to a visitor (Source: Earth Observatory of Singapore)
Tsunamis would be small in Singapore for several reasons. To the west, the island of Sumatra shelters us from waves coming from the Sumatran Subduction Zone, an underwater fault where several major earthquakes such as the 2004 Great Indian Earthquake and Tsunami happened. To the east, where a South China Sea event would come from, it is the shape and shallow nature of the seafloor that plays a crucial role is reducing the tsunami waves coming from the Manila Trench.
Map showing two main subduction zones around Singapore, including the Manila Trench (Source: Earth Observatory of Singapore)
In contrast to Singapore, other Southeast Asian countries and their coastal infrastructure, such as ports, are more exposed to tsunami hazard. A 2024 study involving Prof Switzer and his team found that a large earthquake on the Manila Trench would significantly impact ports around the South China Sea and could damage 11 ports for tens or hundreds of days depending on the location. These damages would disturb shipping routes, impact other ports and cause major economic disruptions in the region.
Map showing results from the scenario where the greatest number of ports (11) are damaged by a Manila Trench Tsunami (here from Zone 2), including simulated maximum tsunami heights (Source: Figure 4 of the publication)
A lot is being done to reduce the tsunami risk around Southeast Asia, but a lot remains to be done. Scientists across the region are still pushing to better understand the tsunami hazard, which includes characterising where tsunamis could strike, how far they would reach inland, and would be the complex currents be affected.
A recent study by Prof Switzer’s team simulated the tsunami hazards in Manila Bay, Philippines, if a magnitude-8.8 earthquake were to strike along the southern Manila Trench. The researchers unraveled the complex sequence of multiple waves that would affect Manila Bay, with the highest waves occurring at the bay entrance headlands and southern coasts, and high current velocities affecting the entire coastline. These local studies are crucial to understand the hazards local communities need to prepare for.
But earthquakes are only one cause for tsunamis, A lot is also being done to investigate the tsunami hazard from other sources, such as eruptions or landslides from undersea volcanoes. A recent study led by Dr Andrea Verolino, a Research Fellow at EOS, reveals that several volcanoes in the South China Sea have the potential to generate small tsunamis for Singapore. Such studies on cascading hazards, a focus of the ‘Integrating Volcano and Earthquake Science and Technology’ research programme, are key to understanding the connections and complexities of the multiple hazards landscape the Southeast Asian region is facing.
Graphic showing different sources for tsunamis (Source: Earth Observatory of Singapore)
While preparing for the current tsunami risk is crucial, we also have to get ready for the risk of tomorrow. Among other factors, rising seas will affect the future tsunami hazard and risk because they will change how tsunamis flood coastal regions. Because of higher sea levels, regions not currently exposed to tsunamis will be exposed to tsunamis in a few decades. A 2024 study led by Prof Switzer’s team shows that rising seas will increase the number of ports affected by a Manila Trench tsunami to 15. Because sea-level rise will not be the same everywhere, studies looking at tsunami hazard and coastal flooding must be done at a local level, using local sea-level projections. This will be crucial to ensure the solutions continue to be adapted to the local context.
For all this research to have positive impacts on the ground, collaborations among scientists regionally and across sectors remain key. Scientists are increasingly aiming to make their research and tools publicly available to accelerate research efforts and bolster their use by a range of stakeholders. Recent publicly available tools to better understand tsunami hazards include the software used to produce tsunami maps for Manila Bay, with information about the height of multiple waves and the associated currents. For these tools to help reduce the tsunami risk of exposed and vulnerable communities, they need to answer questions that are relevant to stakeholders responsible for the preparedness and safety of these communities. The study on ports disruption discussed above provides results, such as how long ports would be damaged for, that stakeholders can use to adapt mitigation plans as appropriate.
A lot is being done to reduce the tsunami risk around Southeast Asia, but a lot remains to be done. Scientists across the region are still pushing to better understand the tsunami hazard, which includes characterising where tsunamis could strike, how far they would reach inland, and would be the complex currents be affected.