Abstract: This paper studied wen'an earthquake with M_S5.1, occurred in Hebei Province on July 4, 2006. Before the earthquake occurrence, the precursory anomalies, such as water mercury of Wang3 well and Wang4 and groundwater level of Panzhuang and Gaocun wells, all showed irregular manifestation. The study results show that the subsurface fluid around the epicenter area has obvious precursory anomalies before earthquakes, but they are not uniform and continuous in space. The same observed item of wells situated in different tectonic location has different anomaly patterns of the subsurface fluid. From the appearing time of those anomalies, the anomalies are mainly concentrated on short-impending stage. The nearer the earthquake occurred, the more anomaly amount was. The anomalies appear earlier in hot water well than the cold one, especially for those wells, situated in geothermal anomalous region. They are more sensitive to the precursory anomalies.

Key words: Wen'an earthquake, Anomaly characteristics, Tianjin region, Subsurface fluid