中文摘要：

利用云南省地震局流动台网记录的2段余震序列的P波初动资料,采用改进的格点尝试法对这2段余震区进行应力场反演,得到大姚地区2个余震发生时段的应力场方向参数。采用应力量值求取方法,结合2003年10月16日地震的剪切应力降和该地震发生深度处的静岩压力估计获得震源区的应力量值,2003年10月16日主震前最大、中间和最小主应力分别为164.07,158.71和153.10 MPa,投影到10月16日主震前断层面上的正应力和剪切应力分别为157.41和5.24 MPa;震后投影到主震断层面上的正应力和剪切应力分别为158.69和0.01 MPa。研究结果表明：震前剪切应力大于震后剪切应力,且其差基本对应着应力降。震后正应力增大,表明摩擦阻力可能导致了破裂的终止。虽然地下的压应力很大,但差应力却很小。这些结果可为地球动力学模拟提供了基础应力场信息。

英文摘要：

Using the P wave first motion information of two aftershocks sequence recorded by temporary stations and the new version of grid points test method, we study the stress field in the aftershock zone and get the stress field directions in Dayao region in the two occurrence time periods of the two aftershock sequences. Using the stress value calculation method, we get the underground stress value in the focal area： Before the earthquake, the maximum, intermediate and minimum principal stress is 164.07, 158.71 and 153.10 MPa respectively. The normal stress and shear stress projected on fault plane is 157.41, 5.24 MPa respectively. The normal stress and shear stress projected on fault plane after the earthquake is 158.69, 0.01 MPa respectively. The results show that the pre-seismic shear stress is larger than that of post-seismic, and their difference corresponds to the stress drop approximately. The increasing of normal stress maybe cause the termination of the rupture on the seismic fault. The underground compressive stress is very large, but the differential stress is small. It provide fundamental stress field information for the geodynamic process simulation.