Abstract: This paper analyzed the typical underground fluid anomalies and the focal mechanism of Wuwei M_L4.1 earthquake occurred on April 6^th, 2018. The results show that the anomalies appeared before the 2018 Wuwei earthquake scattered in the range of 64~233 km. According to the duration, it includes medium-term trend anomalies and short-term anomalies, and most of them are medium-term trend anomalies. These medium-term trend anomalies are abnormal the annual variation of water level. They also have certain regularity on spatial evolution. The medium-term anomalies are distributed along the fracture zone of the Yangtze River. The results of focal mechanism solution show that the direction of the nodal plane Ⅰ is NE and the nodal plane Ⅱ is NW. The P axis (principal axis) is NE70°, and the dip is 7°. The direction of the main compressive stress obtained by the focal mechanism solution of the Wuwei earthquake is as the same as the distribution of the underground fluid anomalies of the earthquake. It probably indicates that the underground fluid response is closely related to the regional stress loading in the seismogenic process.

Key words: the 2018 Wuwei M_L4.1 earthquake, Underground fluid, the Characteristic of anomalies, Focal mechanism