Research on Qianguo M5.8 earthquake swarm on October 31，2013

On October 31, 2013, M5.5 and 5.0 earthquakes occurred successively in Chaganhua Town Qianguo County Jilin province. After no more than 1 month, three earthquakes occurred again at the same epicenter on November 22 and 23, 2013, the magnitude of which were 5.3, 5.8 and 5.0. All these earthquakes made up swarm. The earthquake swarm occurred in the central depression area of the Songliao fault zone in the Northeast fault block area, and the long axis of the meizoseismal area was along the northwest direction. 1 356 earthquakes were recorded in this earthquake swarm, including 5 earthquakes with magnitude larger than 5.0. Seismic sequence was recorded completely. The epicenters of aftershocks were densely distributed as strip along NW. The result of focal mechanism solution shows that the dislocation type of seismogenic fault is thrust with slip. The earthquake swarm may be affected by northeast ward Fuyu—Zhaodong fault and northwest ward Chaganpao—Daozijing fault, and the fracture direction is along the northwest. The result of analysis on existing data suggests that the seismogenic structure may be a NW trending thrust fault buried in the deep basement of the epicenter area (Chaganpao-Daozijing fault). Before M5.8 Qianguo earthquake swarm, there were some seismic anomalies, but the precursory anomalies were more abundant, which gradually approached the epicenter from surrounding area. After the swarm, precursory anomalies diffused from epicentral area to surrounding area. From the time point of view, precursory anomalies were medium-term at first, characterized by breaking yearly change from 2010, then gradually transformed into short-term anomalies, at last imminent-earthquake anomalies characterized by transiting to accelerating decease.