对1970年以来南北地震带北段6级以上地震前的M_L ≥ 3.0地震活动特征进行了分析，讨论了平静或增强现象的特征，并结合主震震源机制解和区域活动性差异，对6级以上地震的平静现象进行较为深入的分析。结果表明，主震前震中区M_L ≥ 3.0地震活动主要存在平静异常，各个区域的平静特征和时间有差异，震中区M_L ≥ 3.0地震平静持续时间的长短与其主震前活动水平密切相关。

In the northern section of the North-South Seismic Belt since 1970 activity characteristics of earthquakes with M_L ≥ 3.0 before M ≥ 6.0 earthquakes are analyzed,and discussed the calm or enhanced characteristics of the phenomenon. On the basis of the main seismic source mechanism and the differences of regional activity,the calm phenomena of M ≥ 6.0 earthquakes are analyzed in depth. The results show that there is clam anomaly of seismic activity of earthquakes in the epicentral area before main shocks. The calm characteristics and time of each region are different. The duration of the calm of earthquakes with M_L ≥ 3.0 in the epicentral area before main earthquake was closely related to the activity level before the main earthquake.

P315

宁夏回族自治区重点研发计划（科技惠民）项目"内蒙古阿拉善左旗5.8级地震后宁夏北部及邻区地震危险性分析"（2016KJHM135）资助