Why is there no precursory anomaly in Wenchuan earthquake?

At present, it is impossible to accurately predict earthquake disasters, but long-term observation and research show that there will be some signs before earthquakes, such as animal anomalies and groundwater anomalies. This has a certain effect on earthquake prevention.

On May 2008 12 and 14: 28, an earthquake of magnitude 7.8 occurred in Wenchuan, Sichuan (east longitude 103.4 degrees, north latitude 3 1.0 degrees). The earthquake affected most parts of the country. Many netizens are questioning why today's earthquake was not predicted. However, when the reporter checked the information on the Internet, he found that many phenomena indicated that there would be an earthquake.

On May 9th, some netizens posted on Baidu Post Bar: 19: 15. I saw a large earthquake cloud in Linyi. I wonder where a strong earthquake of magnitude 6 or above will occur today and tomorrow.

On the same day, people's pictures released news that tens of thousands of small toads suddenly appeared on Dongfeng Bridge in Taizhou City, Jiangsu Province. It is understood that "recently, the river was short of oxygen, and a large number of small toads had to move collectively in order to find new living space".