Abstract: In order to study the spatio-temporal evolution of the precursory anomalies 10 years before the 2008 Wenchuan M_S8.0 earthquake, the epicentral distance of the precursory anomalies is calculated by using the geometric center of the rupture region and the elliptical centerline of the aftershock region. The result shows that precursor anomalies gradually increase about 2 years before the Wenchuan earthquake. The ratio of abnormal items is greater than 25% in the near the source area (about 2 times the source scale). The ratio of abnormal items is 17～24% (about 3～5 times the source scale) in the remote area. There are three different stages of spatio-temporal evolution of precursory anomalies: during the α stage (including α₁ and α₂, 700 to 3000 days before the main earthquake) the anomalies are mainly distributed in the southwest and the northwest area of the Wenchuan aftershocks area. It is shown that the precursors of the far source region and the near source area have the characteristics of outward expansion. During the β stage (300 to 700 days before the main earthquake), the anomalies are distributed in the southwest and northern regions of the aftershock region, showing a large range of anomalies. During the γ stage (Including γ₁ and γ₂, 300 days before the main earthquake), the range of anomaly distribution is wide, and the anomalies are distributed in the Southwest and Northeast of the aftershock area. The anomalies contract to the epicenter (γ₁) in the far source region and extend outward (γ₂) in the near source region. Through the experimental study and mechanical analysis of earthquake preparation process, the results indicate that the three-stage characteristics of precursory anomalies in the process of earthquake preparation may be controlled by the seismogenic body, which is a form of expression in the process of earthquake preparation and a universal feature during the earthquake preparation process.

Key words: The 2008 Wenchuan M_S8.0 earthquake, Precursory anomaly, Spatio-temporal Evolution