Some scientists have been puzzled by the lack precursors to the 8.0-magnitude earthquake that devastated southwest China on May 12. However, other experts believed there had been signs a major seismic event was about to take place.

"There were no foreshocks, and there weren't many minor quakes around the epicenter for quite some time before the earthquake," deputy director of the China Seismological Bureau (CSB) Xiu Jigang said.

He said there were none of the other typical precursors usually used to predict major quakes before the recent disaster, such as anomalies in wildlife behavior and groundwater levels.

According to Zou Wenwei, director of the publicity and education department at Beijing earthquake bureau, earthquakes are still too complicated to forecast, especially because they are so abrupt.

"Human beings have not completely grasped the rules governing earthquakes, and quake forecasting is still globally regarded as a difficult task," he told China Daily.

China's earthquake prediction program was developed when CSB was founded in 1971.

Chinese seismologists successfully predicted a 7.3-magnitude quake near Haicheng, Liaoning province, on Feb 4, 1975. But only a year later, experts failed to forecast the disastrous Tangshan earthquake of July 28, 1976.

Zou explained that it was because the two earthquakes came in different patterns. While the major Haicheng earthquake was preceded by smaller quakes, the quake that devastated Tangshan, like the one that devastated Wenchuan last week, wasn't, as far as anyone could tell.

Some pointed to strange cloud formations as warning signs that the quake was about to take place, and many people said that on May 9, the countryside of Mianzhu, a city near Wenchuan, was besieged by tens of thousands of toads. People also recalled noticing other strange animal behavior at zoos before the quake.

"It is certain that there would be abnormal animal behavior before an earthquake, but abnormal behavior doesn't necessarily always point to an earthquake," said Zou, who is responsible for publicizing earthquake education. "Both weather changes and environmental changes could also cause animals to behave strangely. So when animals begin acting abnormally, it's not easy to figure out why."

Zou believes the same of abnormal behavior among animals in zoos. "People say they saw strange clouds after every quake," he said. "But cloud formations are even more unpredictable."

He Yongnian, an expert with the CSB, said the cloud formation prediction method was first put forward by Japanese scientists, but, like many other methods, it is not yet sophisticated enough to make accurate forecasts.

A Taiwan satellite recorded a sharp drop in ionospheric density above Sichuan before the Wenchuan earthquake, according to a Taiwan newspaper.

(Xinhua News Agency May 21, 2008)