永善－大关7．1级地震序列震源区应力场分析

ANALYSIS OF THE STRESS FIELD IN SOURCE REGION FOR THE YONGSHAN-DAGUAN,EARTHQUAKE SEQUENCE WITH MAINSHOCK MS 7.1

由云南永善－大关Ｍｓ７．１级地震序列中的１１个Ｍｓ≥４级地震的震源机制解和９８个小震震源机制解，分析了震源区应力场的基本图象和变化形态。结果表明，震源区应力场的基本图象和构造应力场的方向相符。Ｍｓ７．１级主震未对震源区应力场的方向产生可觉察的改变。大量小震机制解的空间取向的优势方向与主震机制解一致。取向离散的小震机制解多出现在序列的前期，至序列末期则很少发现。小震机制解由较离散向集中过渡，显示了震源区应力场动态调整的过程。因此，小地震在强震序列中也做出不可忽略的贡献。

On the basis of the focal mechanisms of 11 evevts with Ms≥4 and 98 small events in the Yongshan-Daguan,Yunnan,earthquake(Magnitude of the mainshock is Ms 7.1)sequence,the general patterns and variation of the stress field in source region have been discussed.The results show that the stress field in source region corresponds to the tectonic stress field.The orientation of the stress field in source region didn't change obviously when the mainshock(Ms 7.1)took place.The dominant orientation of the focal mechanisms of many small events accord with that of the mainshock.The small events with scattered orientation of the focal mechanisms appeared mostly in the earlier period,and seldom in thelater period,of the sequence.The orientations of the focal mechanisms of the small events vary from scattering to concentration.Judging from this . a contribution made by a host of small earthquakes can not be ignored.