Three factors combined to make earthquake forecasting one of the most difficult questions around the globe, according to Zhang Xiaodong, vice director of the China Earthquake Networks Center.

Zhang made the remarks at a press conference organized by the State Council Information Office on the afternoon of May 13.

These factors are: First, it is always hard to predict precisely what is going on underground simply by making observations on the surface.

Second: the formation of an earthquake is a very complicated process. Geographical conditions, historical time factors and magnitude all influence earthquakes.

Third: the low statistical probability of an earthquake occurring makes it even harder to forecast even though earthquakes occur every year around the world and some of them are very strong. But inside a single area, the interval between two earthquakes is so far apart chronologically that it is almost impossible to obtain an accurate statistics sample, which is of vital significance to earthquake predictions.

(China.org.cn by Xiang Bin, May 13, 2008)