图15  大同-阳高6.1级地震前后京西北-晋冀蒙交界地区地震b值图

（38°～42°N，111°～116°E，M_L ≥2．0）

Fig. 15  Curve of the accumulated b-values of the

          events in the northwest area of Beijing-

         border land of Shanxi province，Hebei

         province and Inner Mongolia before and

         after the M6.1 Datong-Yanggao earthquake