A tsunami originating from a major earthquake at the Manila Trench could potentially cause widespread and lengthy east Asian port closures, scientists have discovered. There would also a greater disruption to ocean freight shipping than any earthquake-induced tsunami than ever seen before, they also found.
Up to 11 ports – including some ports that are vital in the global economy – could be badly damaged by the most devastating tsunami that could originate from a Manila Trench earthquake. Each of the ports would likely be hit by a tsunami several metres high. The ports particularly at risk of high levels of damage are:
- Batangas (Philippines), 25 days closed
- Chu Lai, Vietnam, 99 days closed
- Danang, Vietnam, 14 days closed
- Hong Kong, China, 31 days closed
- Huizhou, China, 19 days closed
- Kaohsinug, Taiwan, 53 days closed
- Manila, Philippines, seven days closed
- Palawan, Philippines, 62 days closed
- Qui Nhon, Vietnam, 69 days closed
- Subic Bay, Philippines, 60 days closed
- Zhuhai, China, 41 days closed.
Lengthy closures of ports like Hong Kong, Kaohsiung, and Huizhou would clearly pose a significant disruption risk to global shipping. But, it should be noted, there were several other Manila Trench earthquake induced tsunamis that could affect ports in different ports of the South China Sea. Each tsunami would have different effects. But, as the researchers noted: “Ports in the southeastern coasts of China i.e. Hong Kong and Zhuhai, as well as Kaohsiung port (south Taiwan) are amongst the most vulnerable in a Manila Trench tsunami. Hong Kong and Zhuhai are consistently damaged in all scenarios, whereas Kaohsiung port is damaged in tsunamis [in other scenarios]. With Kaohsiung and Hong Kong ports being amongst the world’s 50 busiest ports, a Manila Trench tsunami can have dire consequences for maritime trade and the local economy in these ports”.
Under sea-level rise conditions out to 2100, the researchers concluded that the damage would likely be more widespread with the eleven ports as listed above very likely being badly damaged alongside the ports of Kota Kinabalu, Malaysia; Miri, Malaysia; Quanzhou, China; and Xiamen, China.
Commenting on the risk, the researchers wrote that: “a comprehensive picture of the potential risks across the domains – from individual ports to the entire port network, is necessary for the different stakeholders i.e. port authorities, port operators, shipping and logistics companies to work together to minimise the impacts of port disruptions”.
Manila Trench – why it could generate an ocean-wide tsunami
A Manila Trench mega-earthquake is particularly relevant to ports and shipping because tsunamis can travel an awfully long distance away from their point of origin, there are many major ports surrounding the south China Sea – many of which are in low-lying coastal areas, and there’s more than a little bit of shipping that relies on ports in the region. Geoscientists and historians have long known that the Manila Trench area is capable of producing big earthquakes.
The Manila Trench, as its name suggests, is a deep oceanic trench located to the north-west of the Philippines, near the capital city of Manila. It’s about 5,400 metres deep, which is roughly as deep as the Ritacuba Blanco mountain, located in the Andes mountains of Colombia. The Manila Trench exists because of the actions of the movements of the plates of the Earth – one of the plates is sliding below another just to the north west of the Philippines. And so the area is already associated with earthquakes. There have been six quakes recorded since 1924 that have had a score equal to or greater than 6.4 on the “moment magnitude scale”. It’s a logarithmic scale, so each unit is a multiple of a base (i.e. a scale that runs 10, 100, 1000 is an example of a logarithmic scale as opposed to a scale that runs 1, 2, 3, 4, 5 etc which is a linear scale).
An earthquake at a scale of six would result in moderate property damage while a quake at scale seven would result in loss of life and billions of dollars of property damage.
Working out the scale of the threat to ports and shipping: the 2011 Tohoku tsunami
The scientists noted that earthquake-induced tsunamis caused extensive disruption to shipping and ports in the past but they also noted that there isn’t a full understanding of the phenomenon. Observing that the 2011 Tohoku tsunami caused around USD$12 billion in damage to port facilities and ships, and that the subsequent port disruption caused losses in seaborne trade of about $3.4 billion a day, the researchers commented that “the impact of a tsunami on ports has considerable economic consequences beyond physical damage… [there is a] large disparity between the primary and secondary effects of a port damage,” while adding that the impact of tsunami-induced disruptions on ports is lacking. As there is a shortage of knowledge owing to the infrequency of tsunamis, there is a lack of observations on how tsunamis interact with modern port infrastructure. Even though there have been several large tsunamis in the last few decades, the researchers found that there are few publicly available records of port / port infrastructure response to tsunamis.
But there is at least one good case study.
“The 2011 Great East Japan (Tohoku) earthquake-tsunami serves as a great starting point for us to understand the response of port structures to tsunami impacts, due to the extent and severity of the damage observed as well as the large ensemble of observational data documented post-tsunami,” the researchers wrote, adding that the 2011 tsunami demonstrated that inundation greater than 2.5 metres creates a greater than 90% probability of damage to port structures. In the 2011 Japanese tsunami, 13 out of 19 ports sustained damage and lost their functionality when tsunami heights exceeded 3.3m.
Simulations, simulations, simulations
The scientists carried over 100 simulations and there were eight potential sources of earthquakes from three different segments of the Manila Trench that were identified as being capable of generating tsunamis across the South China Sea. The the likely effects on the global liner shipping industry were estimated using mathematical analysis on data presented in previous academic studies where those earlier papers used Alphaliner-sourced data. They based their analysis on 966 ports and 16,533 shipping routes.
Simulations were modelled at present-day sea levels (remember: the higher the sea level, the greater the size of the tsunami and the greater the damage to port infrastructure) and also where planetary climate change leads to higher global temperatures between 33.3 to 5.7 degrees Celsius and higher sea levels.
Several different areas of the Manila Trench were considered as being capable of generating highly-damaging tsunamis. The researchers focused on an area they labelled “Z2B”, which is the area of the Manila Trench that runs along the coast of north western Luzon (the very large northern Philippine island) from a latitude roughly level with Santiago Island to a latitude approximately level with the northernmost tip of Luzon island.
Researchers, journal and citation
Research was carried out by Chua, C.T., Otake, T., Li, T. et al of the International Research Institute of Disaster Science at Tohoku University, Japan, alongside Switzer, A. of the Earth Observatory of Singapore, Nanyang Technological University, Singapore, in “An approach to assessing tsunami risk to the global port network under rising sea levels,” in the journal of Natural Hazards (npj Nat. Hazards 1, 38 (2024)) doi.org/10.1038/s44304-024-00039-2.
