By Bill Smith, DPA,
Beijing : No significant precursory seismic activity was detected that could have allowed the Chinese government to issue a clear warning before the devastating earthquake in the south-western province of Sichuan, a leading international seismologist said.
“I had nothing unusual at all that you would regard as precursory,” Gary Gibson of the Seismology Research Centre at Monash University in Melbourne, Australia, told DPA by telephone Friday.
“There were not even moderate events,” Gibson said of the period before Monday’s quake, which international seismologists have upgraded to 7.9 on the Richter scale.
Some Chinese and foreign media reports have focussed on a 2002 report by Chen Xuezhong, a researcher with the China Earthquake Administration, who warned of the “virtual certainty” of an earthquake of at least 7.0 on the Richter scale in the area within the following few years.
A Chinese scientist said in his blog this week that semi-retired seismologist Geng Qingguo, who is known in China for accurately predicting the 1976 Tangshan earthquake, had also predicted the Sichuan earthquake.
Other reports claimed that cloud formations and an exodus of toads were clear precursors that government experts should have recognised.
Gibson visited China several times and studied the 7.8-magnitude quake that killed at least 240,000 people around the northern city of Tangshan in 1976. Controversy remains about whether Chinese leaders or top seismological officials, who were sidetracked by fierce infighting within the ruling Communist Party, ignored predictions by Geng and other experts of a major quake in Tangshan.
In the political turmoil following the end of the 1966-1976 Cultural Revolution, state media did not even report the Tangshan quake for three years.
“Retrospectively, there was enough data,” Gibson told DPA in an earlier interview on Tangshan. “Precursors were recorded but not recognised.”
In 1976, seismologists still made significant use of ancient techniques for earthquake prediction, such as monitoring ground water and analysing the behaviour of wild animals.
“That’s losing favour everywhere, but it’s still not totally (gone),” Gibson said of the observation of animal behaviour in earthquake prediction.
Gibson, who has met many contemporary Chinese seismologists at international conferences, believes they are generally “very good”.
“The best of them are certainly world leading standard,” he said.
He said that some ancient earthquake-forecasting techniques were still scientifically useful.
Unusual water levels in wells, for example, could be “directly a result of stress changes” in underground rock formations, he said.
Monday’s earthquake in Sichuan occurred as a result of ongoing pressure from the Indian sub-continent, which is pushing up the Himalayas as it presses northwards into the Eurasian tectonic plate at a speed of about 50 millimetres per year.
Most of Sichuan lies on the edge of the Tibetan plateau to the northeast of the Himalayas.
The epicentre of the devastating quake Monday, which is estimated to have killed more than 50,000 people, was in Wenchuan County along a well-monitored fault in Sichuan’s Longmen Mountains.
Senior researcher Zhang Guomin Friday defended the China Earthquake Administration’s record on Wenchuan, saying its predictions were based on risk analysis.
Warnings could only be issued when there was “evidence of a highly probable earthquake”, state media quoted Zhang as saying.
Zhang rejected rumours that the government deliberately withheld information on the possibility of an earthquake to avoid influencing preparations for the Beijing Olympics in August.
“This is absolutely groundless, earthquake forecasting is based on strict scientific analysis,” he said of the rumours.
A Taiwanese satellite recorded a sharp drop in ionospheric density above Sichuan before the Wenchuan earthquake, adding to growing evidence that seismic activities have electrical effects on the atmosphere, the Taiwan-based China Times reported Friday.
The newspaper said that Taiwan’s Formosa-3 satellite recorded ionospheric density in the atmosphere of 1.2 million electrically charged particles, in some 1,000 sq km around Wenchuan, six to 15 days before the May 12 earthquake.
On May 11, the eve of the quake, the ionospheric density had dropped by half to 600,000 charged particles, it said.
“There’s absolutely no doubt that there are electrical precursors,” Gibson said, citing previous evidence of the effect of seismic activity on low-frequency radio signals used in submarines.
But he said the satellite recording of ionospheric changes may not be practical to use in earthquake forecasting.
“I don’t think you could do it reliably,” he said. “It would be difficult to do it quickly.”
“There will never be a black-white yes, there will be an earthquake of this magnitude at this place at this particular time, “Gibson said.