利用小震震源机制解研究宁夏南部及邻区构造应力场
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摘要
利用垂直向Pg和Sg波振幅比方法计算了2003年1月至2009年10月间宁夏南部及邻区的40个中小地震的震源机制解,然后对计算所得的40个地震的震源机制解进行系统聚类及应力场分析,利用格点尝试法研究灵武—吴忠地区(I区)和宁夏南部地区(II区)的平均震源机制解。结果表明:该区域主要受北东东向压应力作用而形成右旋走滑型断层,同时又带有张性分量;I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;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东向发生压缩,北北西向发生相对扩张。
Firstly,we calculated the focal mechanism solutions of 40 small and moderate earthquakes in southern Ningxia and its adjacent areas from Jan. 2003 to Oct. 2009 by the amplitude ratio method of Pg and Sg waves in vertical direction and did the system clustering of the calculated focal mechanism solutions to analyze the stress field. Secondly,we studied the average focal mechanism of Lingw u-Wuzhong region( I) and southern Ningxia region( II) by grid testing method. The results show that it is easy to develop dextral strike slip fault with stretching component in the study area under the compressive stress in NEE. The direction of principal compressive stress of tectonic stress field in I and II region is mainly horizontal. The structure deformations in the focal region caused by earthquake are compression in NE and expansion in NW in I region,and are compression in NEE and expansion in NNW in II region.
引文
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