利用多个震源机制解求东大别地区平均应力场

Determination of mean stress field in eastern Dabie region from focal mechanism solution analysis

利用地震的震源机制解资料,得到应力张量在地理坐标系下的表达式,进而可计算平均应力张量.通过求平均应力张量的本征向量,即可得到其主轴方向,并由此推断区域应力场方向.利用东大别地区219次地震的震源机制解资料,比较了不同相似程度和不同起算震级资料得到的主轴方向,认为该方法计算结果非常稳定,主轴方位角的误差小于5°,倾角的误差小于10°.计算结果表明,东大别地区最大主压应力轴σ1的方位角为267°,倾角为5°;最小主压应力轴σ3的方位角为358°,倾角为4°.表明该地区受东西向的水平挤压和南北向的水平拉张作用.

By stacking focal mechanism parameters of a group of earthquakes we present an expression of mean stress tensor for a region in geographic coordinates. We calculated average stress tensor and its eigenvectors to get the directions of principal axes, which may represent the directions of regional principal stress axes. By analyzing focal mechanism parameters of 219 moderate and small earthquakes we have inferred mean principal stress directions for this region. Results of testing this method by sampling different data sets indicate that this method is simple in use and the results are stable. The error of azimuth of principal axes is estimated to be less than 5°, and that of plunge is less than 100. The mean regional stress parameters we obtained are as follows： The azimuth of maximum principal （compressive） stress axis （compression axis）, σ1,is 267°and its plunge is 5°; azimuth of minimum principal （compressive） stress axis （tension axis）, σ3, is 358°and its plunge is 4°. This indicates that the eastern Dabie region is horizontally compressed nearly in E-W direction, and its relative horizontal extension is nearly in N-S.