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Stephen Chen


The risk of a major tsunami in the South China Sea has been underestimated, even ignored, by governments in the region, say scientists from the mainland, Taiwan and the Philippines.
The effect could be devastating, with the loss of hundreds of thousands of lives in coastal areas including Hong Kong.
One of the scientists involved, from the Chinese Academy of Sciences' Institute of Oceanology, said they desperately needed fresh data to gauge the potential tsunami's possible size and how soon it might occur. They need to go to the area to get it, but the current conflict over sovereignty prevents them from doing so.
Dr Qian Jin, a marine geologist with the institute in Qingdao , Shandong , said in an interview in June he used a new mathematical model to analyse historical seismic data collected by mainland research vessels along the Manila Trench.
The results unnerved him.
The trench stretches about 350km from southern Taiwan southward to the west coast of Luzon, the largest island of the Philippines. The trench's depth is about 5.4km, about 3.5 times the average depth of the South China Sea.
It's where the gigantic Eurasian Plate hit and dived under the ancient Philippine Sea Plate. The trench is also very close to the Scarborough Shoal, or Huangyan Island, which both China and the Philippines claim.
The Manila Trench has shown signs that it could experience a large earthquake. Scientists have shown concern, and Qian's analysis added to it.
Because the new modelling tool can measure the trench's geophysical structures with higher resolution, Qian discovered that the actual length of the trench's fault zone, which can trigger a tsunami, was "noticeably" longer than previously reported. That means the trench's ability to breed a large earthquake and tsunami might have been underestimated.
Though the exact size of the fault zone is still being calculated, Qian said he felt obliged to inform the public about the risk.
But he says a better job of analysing and predicting what will happen depends on getting new evidence. "The data we used was old, collected more than a decade ago," Qian said. "We want new data, but we can't go there any more. The area is full of trouble. We dare not get close to the Philippine side.
The Manila Trench has not produced a major earthquake for five centuries, which makes geologists edgy.
"The trench has been taking stress for a long time. An enormous amount of energy is trapped inside. If an earthquake occurs, it can be a huge one," Qian said.
Dr Tso-Ren Wu, an assistant professor at the Institute of Hydrological Science at the National Central University in Taiwan, said Taiwan was particularly vulnerable, not only because it was close to the northern tip of the trench, but also because there's a large nuclear power plant on the southern coast.
"If the earthquake reached certain magnitudes, even Hong Kong could be devastated. The situation could get worse if the nuclear plant at Daya Bay [in Shenzhen] was affected," Wu said.
Dr Renato Solidum, director of the Philippine Institute of Volcanology and Seismology, told local GMA News in April that a magnitude 8.2 earthquake in the Manila Trench could trigger tsunamis 10 metres high that would reach the Philippines' shores in five to 10 minutes, and Manila would flood in about an hour.
Wu said the most effective method to monitor the risk would be to lay down cables with sensors on the ocean floor. The sensors could collect accurate, real-time data on the trench's activities, which would allow scientists to measure and understand its movements.
Taiwanese authorities placed numerous buoys in various locations, but they became damaged.
Professor Mao Xianzhong , a tsunami risk researcher at Tsinghua University, said China had also deployed two state-of-the-art tsunami warning buoys, each costing more than US$10 million, near the Manila Trench, but they met the same fate. It's unclear whether they had been damaged intentionally.
Mao said their simulations showed earthquakes in the Manila Trench of magnitude 8 or above could bring disasters to southern mainland coastal areas with waves up to five metres high. Hundreds of thousands could be killed, he said.
"The governments must put aside political disputes and work together on the project as soon as possible."
Professor Sun Liguang and his team at the University of Science and Technology of China announced last year they had discovered evidence of a huge tsunami, likely from the Manila Trench, that devastated a coral reef in the Paracel Islands some 1,000 years ago.
There is also a theory that the Manila Trench has a big jolt every 500 years, and the last one was about 500 years ago.


Disputes over sovereignty hide quake and tsunami danger in Manila Trench

News

China

As countries clash over sovereignty in the region, scientists are unable to do crucial research on the quake-prone Manila Trench


The risk of a major tsunami in the South China Sea has been underestimated, even ignored, by governments in the region, say scientists from the mainland, Taiwan and the Philippines.
