Historic earthquake activity in the north China region has been intense. However, no moderate earthquake has occurred in the last more than ten years in the region since the 1998 Ms6.2 Zhangbei earthquake. The quietness of moderate to strong earthquake is quite prominent in the region. In this paper, we use the small earthquake record between 1970 and 2009 to study the background seismic activity in the north China region. We presented the spatial distributions of seismic parameters including b-value, maximum magnitude and annual probability of occurrence of an earthquake equal to or larger than M6.0.Our results show that the regions with low b-value include the Yunchen region in the Shanxi rift, the Shuqian region located in the Tanlu Fault Zone and the Shijiazhuang region in the Taihangshan block. The analysis by synthesis shows that seismicity in the north China region is mainly affected by the regional dynamic factors in depth.%华北地区的历史强震活动非常频繁.然而,自1998年张北Ms6.2地震以来,该地区已经经历了10多年的地震平静期,中强震平静现象比较突出.本文利用1970年至2009年的小震资料,对华北地区的背景地震活动进行分析,给出了地震活动性参数b值、最大震级以及强震复发间隔和强震年平均发生概率的空间分布.b值空间分布表明,山西构造带的运城地区,郯庐断裂带的宿迁地区以及太行山块体内部的石家庄地区的b值较低.地震活动性参数的综合空间图像表明华北地区的地震活动主要受区域深部动力因素所控制.
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