【摘要】 依据2002—2006年的中小地震资料,利用格点尝试法分析计算了华北北部4个应力小区的平均主应力轴.讨论了华北北部地区的现今应力场特征.在此基础上,对1977—1998年研究区内的单个地震震源机制解进行了进一步的分析计算,并结合以往的研究结果.研究了华北北部地区现今应力场随时间的变化特征,结果印证了唐山地震前后,唐山震源区及其邻近地区应力场主应力方向出现的转动和变化的现象:1976年唐山发生7.8级地震后,唐山震源区及其邻近的北京地区和邢台地区震源机制解的平均P轴可能顺时针转动了约15°—30°.北京地区和邢台地区近期(2002—2006年)的平均主应力轴与唐山地震前的综合断层面解较为一致,这两个地区应力场似乎转回到唐山地震前的状态.而唐山区震源机制解的平均P轴在地震后则一直稳定在EW向上.位于张家口—渤海断裂带西段的京西北地区,其现今应力场则相对比较稳定。唐山地震前后主应力方向没有太大变动.鉴于数据资料等方面的原因,本文的研究结果仅仅是初步给出了华北北部地区应力场近几十年来一种可能的调整变化图象.更多还原

【Abstract】 From focal mechanism solutions of the earthquakes in northern part of North China during the period of 2002-2006,the directions of principal stress axes in 4 stress sub-regions are analyzed using a grid test method.The charac- teristics of present crustal stress directions is discussed.Based on this result and on the focal mechanism solutions calculated for some events in the period of 1977-1998,in combination with some other study results,the temporal varia- tion of the present crustal stress directions in northern part of North China is in- vestigated.The results confirm that the direction of crustal principal stress in some regions had somewhat rotated after the 1976 Tangshan M7.8 earthquake. The mean P axes of the focal mechanism solutions rotated clockwise not only in Tangshan sub-region,but also in Beijing and Xingtai sub-region after the Tang- shan earthquake.In Beijing and Xingtai sub-region the orientations of principal stress axes in the period of 2002--2006 are consistent with that before the Tan- gshan earthquake,implying that the stress orientations has rotated back to the state before the Tangshan earthquake in these two sub-regions.The directions of the mean P axes are nearly E-W in Tangshan sub-region since the M7.8 earthquake.The present stress field in the sub-region northwest to Beijing,or in western part of the Zhangjiakou-Bohai fault zone,is relatively stable during the time period concerned in this study.Because of the limitation of data,this paper only states a possible variation of the stress field in northern part of North China in recent decades.更多还原