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

By using focal mechanism solutions, we present the expression of stress tensor in geographic coordinates. And then calculate average stress tensor and its eigenvectors to get the direction of principal axis,which can be extrapolate the direction of regional stress field. According to the focal mechanism solutions of 219 earthquakes in East Dabie, the analysis result of directions of principal axis in different similarity and magnitudes are given. This method is simple and the result is stable, the error of azimuth of principal is less than 5 deg; and the plunge is less than 10deg;. The result shows that the azimuth of principal axis sigma;1 is 267deg;, the plunge is 5deg;; the azimuth of principal axis sigma;3 is 358deg;, the plunge is 4deg;. It can be indicated that the East Dabie is forced by horizontal compression in EW and horizontal extension in NS.