Statistical analysis of pre-seismic anomalous characteristics of subsurface fluids in Yunnan region

Based on the information collected from the Earthquake Cases in China from 1966 to 2006, this paper carries out a statistical analysis of the subsurface fluids precursory anomalies of M_S≥5.0 earthquakes in Yunnan Province. The results showed that: ① More than 70% water level and water temperature anomalies were observed rising before the earthquakes, and radon and water level anomalies appeared much earlier than temperature anomaly. ② The larger the earthquake magnitude, the larger the corresponding anomaly area of the fluid. ③ Most pre-seismic fluids anomalies persist until the earthquake occurs, indicating that they were related to pre-earthquake crustal activity, and a set of empirical boundary equations were obtained in an attempt to assist in the future earthquake prediction. Five types of groundwater anomaly were identified according to the summary of the abnormal morphology of groundwater, including trend turning class, period class, mutation class, threshold class and synthesis class, and typical cases, as well as possible reasons for each type were presented. The results of this paper could be helpful for understanding the abnormal characteristics of fluid and improving the application of fluid anomaly in the Yunnan region.