自Global CMT和前人文献中搜索了1973~2015年间的34条中小地震震源机制解并进行分析，根据震级对每个地震震源机制解进行加权处理，采用网格搜索法反演了川滇菱形块体中部区域现今构造应力场。结果表明，川滇菱形块体中部区域整体以走滑断层类型为主，而西部呈现正断层类型；整个区域应力场受到近NW向挤压，NE向拉张，应力形因子为0.1。该区域应力场主张应力轴方向近水平，表明有横向的拉张作用。较低的应力形因子表明几乎处于NW-SE向和垂直向的双轴挤压及NE-SW向拉张的应力状态。这种应力状态来源于2种动力作用：①在青藏高原物质东流和华南块体阻挡作用下呈现NW-SE向挤压和NE-SW向拉张的走滑应力状态；②印度板块缅甸弧对该地区深部的NEE向低角度俯冲作用导致浅部地壳物质具有NEE-SWW向的拉张分量。这2种动力的共同作用导致该地区既出现走滑型地震，又出现正断型地震。

The 34 focal mechanisms are selected from Global CMT and publications during 1978-2016 and analyzed. After weighting each focal mechanism according to its magnitude,the present tectonic stress field in the central region of Sichuan-Yunnan blocks is inverted using grid search method. The results show:The focal mechanisms primarily show strike-slip types in the central region of Sichuan-Yunnan block,but normal fault type in the west. The regional stress field is nearly NW compression and NE extension;the stress shape factor is estimated to be 0.1. The extensional axis of the stress field is nearly horizontal,which shows lateral extension action in this area. Lower stress shape factor suggested nearly biaxial compressional stress in NW-SE and up-down direction and larger NE-SW extensional stress. The stress state results from two effects:(1)the NW-SE compression and NE-SW extensional strike slip stress state due to the Qinghai-Tibetan Plateau's material eastward flowing and the blocking of the Southern China Block.(2)NEE-SWW extension in the shallower crust resulted from the subducting in the depth of the Burma Arc. Both the effects contribute to the occurrence of strike-slip and normal faulting earthquakes.

P315

国家自然科学基金项目（41674055、41704053）、河北省地震局地震科技星火计划项目（DZ20170109001）共同资助