图21  京津唐渤张东区地震活动性参数随时间的变化^［11］

Fig.21  Variation of seismologic activity parameters with time in the east area of         Beijing-Tianjin-Tangshan-Bohai-Zhangjiakou

① M_L≥3.0 级地震频度;  ② 2.0＜M_L＜3.0地震频度;  ③ 1.5≤M_L≤2.0地震频度