利用小震震源机制解研究宁夏北部及邻区构造应力场

利用垂直向和波振幅比方法计算了2003年1月至2009年10月间宁夏北部及邻区的31个中小地震震源机制解，然后对计算所得的31个地震震源机制解进行系统聚类及应力场分析，并利用格点尝试法研究阿拉善区域（I区）和银川盆地及以北地区（II区）的平均震源机制解。结果表明：31个中小地震中走滑型地震占了近77％，显示出宁夏北部及邻近地区地震错动方式以近走滑为主；I区域地震产生的震源区构造变形是近南北向发生压缩，近东西向发生相对扩张；II区域构造应力场主压应力方向以水平作用为主，地震产生的震源区构造变形是北东向发生压缩，北西向发生相对扩张。

CHARACTERISTICS RESEARCH OF TECTONIC STRESS FIELD ON NINGXIA NORTHERN REGION AND NEIGHBORING AREAS

In the paper, we calculated focal mechanism solutions of 31 small and moderate earthquakes occurring in Ningxia and neighboring areas from Jan. 2003 to Oct. 2009 based on amplitude ratio of and of vertical records. Then, we analyzed the stress field by system clustering and average focal mechanism of Alashan region （I） and Yinchuan basin and its northern region （II） by grid testing method. The results show that 77% of 31 earthquakes are strike-slip earthquakes and seismic dislocation mode is mainly strike-slip mode in Ningxia northern region and neighboring areas. Principal compressive stress direction of tectonic stress field of region II is mainly horizontal directions. Structure deformations of focal region caused by earthquake occurring in region I are nearly NS compression and nearly EW expansion, and that in region II are NE compression and NW expansion.