By Sun Xiaohua (China Daily)
Updated: 2008-05-16 10:26

Neither the migration of toads nor unusual cloud formations were clear indicators of an impending earthquake, the country's seismological authority said on Thursday.

According to some media reports, forecasters ignored the warning signs, such as the mass migration of toads in Mianzhu, just three days before the earthquake happened.

Zhang Guomin, a senior researcher at the China Earthquake Administration, said on the government's website that predictions cannot simply be based on the movement of animals.

Earthquake predictions are based on risk analysis, and warnings can only be issued when there is evidence of a highly probable earthquake, he said.

Zhang Xiaodong, a scientist with the China Earthquake Networks Center, said it is difficult to predict earthquakes because they often take place deep underground where detection equipment cannot be placed, and their occurrence depends on the surrounding geological structure.

This makes it difficult to obtain meaningful samples to analyze, he said.

"Studies by Chinese scientists have yet to reach a definite conclusion on whether the abnormal behavior of animals is a result of environmental conditions, climate change or an earthquake," Zhang Xiaodong said.

"We are still studying the evidence."

Other media reports said unusual cloud formations were also a warning of an earthquake.

But Xiu Jigang, deputy director of the China Earthquake Administration, said cloud formations frequently change and therefore are not reliable in predicting tremors.

As for rumors that China withheld information on the earthquake because of the Olympics, Zhang Guomin said: "This is absolutely groundless. Earthquake forecasting is based on strict scientific analysis."