Research on the Precursor of Moderate Earthquakes before M.GEQ.5.0Seimic in the Northeast Region

In this paper,three parameters(E,T,and R) were used as tools to describe the activities of moderate earthquakes defined by statistical analysis of 11 earthquakes(M≥5.0) in the northeast region of China.The results showed that seismic activity in this area had obvious regional characteristics such that intense seismic activity of ML≥4.0 earthquakes was observed prior to all M≥5.0 earthquakes in Liaoning and to the west of the Nenjiang fracture.The final moderate earthquakes prior to the M≥5.0 earthquakes generally occurred within six months.The interval average was three months;the shortest period was 0.7 month in Liaoning Province.In addition,the interval ranged from two to nine months with a four-month average west of the Nenjiang fracture.However,intensive moderate earthquake activity was not observed prior to M≥5.0 earthquakes east of the fracture.The probability of the expected M≥5.0 earthquake occurring in the area of Yingkou-Haicheng-Xiuyan was more than 75%,which was accompanied by enhanced moderate earthquake intensity.If a foreshock sequence existed,its epicenter was located in the scope of 22 km near the larger earthquake.Essentially,the epicenter of M≥ 5.0 earthquake occurring to the west of the Nenjiang fracture was located in the vicinity of the initial or latest moderate earthquake area,at a distance of 11~67 km.Therefore,the ETR method has some significance in determining the epicenter of next M≥5.0 earthquake after the occurrence of moderate seismic activity.