Abstract:The Wenchuan MS8.0 earthquake caused widespread attention. To determine whether earthquakes can be predicted and whether anomalies are present before earthquakes, several scholars have previously studied a summary of the precursory data of the Wenchuan earthquake. On the basis of such previous research, the present study analyzes the anomalies of underground fluid present before the earthquake. By using the methods of medium-term anomaly, short term and imminent abnormalities, co-seismic variation, and the adjustment after the earthquake, this study analyzes the data of water radon, water level, water temperature, and flow. Using the subordinate function extraction for recognition and extraction of the medium term anomaly proved to be effective. The Wenchuan MS8.0 earthquake, with intensity up to XI, caused inestimable human and economic losses in the affected areas involving 125,500 km2 in 247 counties, cities, and districts. 69,180 people died, 374,008 were injured, and 17,406 were reported missing. More than 10 million people were affected. 785.88 million houses collapsed, and 2,421.54 million were severely damaged. The direct economic damage could substantially exceed RMB 845.1 billion. This disaster occurred for four main reasons. First, the earthquake had a large magnitude, high energy, and shallow focus. Fracturing lasted up to 90 s, and the earthquake excitation was more powerful in the fracture zones. Second, because the fracture surface continued for several hundred kilometers through the town, the earthquake wreaked havoc on the buildings. Third, the earthquake occurred in the mountains. Fourth, secondary effects aggravated the disaster. Field investigation and the precursory data research by previous scholars revealed that the Wenchuan earthquake included macro-precursor abnormalities and seismic effects. This earthquake had the largest magnitude of those occurring in north-south seismic belt in recent years. Therefore, it is necessary to summarize the Wenchuan earthquake precursor anomaly.In recent years, China’s seismic monitoring network has become denser, and the observation scale has become greater. Data have been accumulated for moderate earthquakes. In addition, many achievements have been in fundamental theories, earthquake prediction methods, and the precursory mechanism. In the history of more than 40 years of earthquake monitoring and forecasting, 20 destructive events have been predicted with varying degrees of success. Despite some progress in the method of forecasting, it is quite difficult to predict earthquakes. Therefore, earthquake prediction is still in the primary stage. Although the Wenchuan earthquake was not predicted, some abnormal fluid phenomena appeared before the earthquake. By summarizing and analyzing data after the earthquake, some scholars detected 28 credible underground fluid anomalies within 1000 km in addition to 11 suspected abnormalities and 194 coseismic abnormalities. A month after the Wenchuan earthquake, the China Earthquake Administration subsurface fluid disciplinary technical coordination group found 39 suspected underground fluid abnormalities within 1,000 km from the epicenter. According to the Sichuan Seismological Bureau of Statistics, nine underground fluid anomalies may be related to the Wenchuan earthquake. Despite an exception, it is certain that subsurface fluid exists before the earthquake anomalies. The following exception is divided into short-term, short-Pro, and coseismic anomalies, which are discussed in this paper.
