Medium term prediction before zhangbei M6.2 earthquake

Before the occurrence of Zhangbei M_s6.2 earthquake, anomalous characteristics were clearly showed in regional seismicity. In recent years, the authors have paid high attention to the changes of seismic trend within the area from northwestern Beijing to the boundary of Shanxi, Hebei and inner Mongolia, and have proposed that the danger of a strong earthquake existed in the northern part of North China based on the general variations of seismicity in Noth China area in the years passed. Particularly from October to November in the year of 1997, they made a medium term prediction for an earthqake of M_s6-7 which might occur in the end of March (with an uncertainty of 5 months) of 1998 in North China area. After emphasized the characteristics of multisource seismogeny in North China area, they suggested that "since some precursory anomalies of seismicity appeared earlier in time and long in duration within the area from northwestern Beijing to the boundary of Shanxi, Hebei and Inner Mongolia, attention must be paid for a strong earthquake which may first occur in this area.