利用2008—2019年云南及其邻区3 121次M≥2.5地震的震源机制解资料,采用叠加应力场反演方法反演了不同时段云南地区应力张量方差空间变化和2014年3次强震震区的时间变化,分析了强震前后震源机制一致性参数的时空演化特征。结果 表明:3次强震震中位于应力张量方差低值区域或其边缘,各震源区震前空间演化存在明显的区域差异性,地震发生后应力张量方差快速回升,同时在滇西和滇南—滇西南地区形成2个低值区域; 3次强震前3～5年震源区应力张量方差变化过程总体呈正“V”字型,下降过程持续2年左右后开始转折并趋势回升,在正“V”字型形成过程的趋势回升阶段发生地震,回升至发震的时间间隔为1～3年。初步分析认为,3次强震前震源区的震源机制趋于一致是孕震过程中应力增强的一种表现,随着时间推移应力张量方差趋势下降后发生转折,表明发生强震的危险性增强。
Using the focal mechanism data of 3 121 earthquakes ML≥2.5 in Yunnan from 2008 to 2019,the spatial variation of the variance of the stress tensor and the temporal variation of the three strong earthquakes in 2014 were inversed by using the method of superposition stress field inversion,the temporal and spatial evolution characteristics of focal mechanism parameters before and after strong earthquakes were further analyzed.The results show that the epicenters of the three strong earthquakes are located in the region or the edge of the low variance of the stress tensor,and there are obvious regional differences in the spatial evolution before the earthquakes in each seismic region.The variance of stress tensor rises rapidly after earthquake,at the same time,two regions with low variance of stress tensor are formed in Western and south-southwest Yunnan.Change process about variance of stress tensor in the focal region generally showed a positive “V” shape in the three to five years before the three strong earthquakes,the descending process lasted for about two years and then began to turn and trend to rise again,the earthquake occurred in the rising phase of the “V” shape forming process,and the time interval between the rising and the occurrence of an earthquake is 1 to 3 years.The preliminary analysis shows that the focal mechanism of the source region before the three strong earthquakes tends to be the same,which is a manifestation of the stress enhancement in the seismogenic process.The turning point of the stress tensor variance after the decreases with time indicates that the urgency of strong earthquake is increased.
