关键词: 华北, 活动断裂, 应力状态, 地震活动, 失稳机制

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