Abstract: 49 sets of in-situ stress measured during 1966～1984 in North China have been used to calculate the effective stress ratio on active fault plane near measuring site. A certain relation was found between the variation of the ratio of effective normal stress to shear stress with time and seismicity. Because of the difference of seismicity at various sections, the corresponding effective stresses are different, even if along the same fault in the same time period. It can be thought from the analysed data that for the effective stress less than 0.5, the seismicity along the fault is weak and the fault is stable, and on the contrary, it is not stable.

Key words: North China, Active fault, Stress state, Seismicity, Instable mechanism

摘要： 采用我国华北地区1966～1984年原地应力测量数据49组,结合各测点附近主要活动断裂的几何要素进行了分析,发现地壳浅部断裂面上的有效正应力和剪应力的比值随时间变化与断裂附近地震活动存在某种对应关系。即使在同一断裂上同一时域内,由于不同地段地震活动性的差异,所对应的有效应力比值亦有不同的变化。分析认为,当断裂面上有效应力比值在0.5以下时,断裂附近地震活动微弱,断裂呈现稳态,大于此值时,地震活动增强,断裂失稳。

关键词: 华北, 活动断裂, 应力状态, 地震活动, 失稳机制