华北地区中小地震应力场的优势方向

根据华北地区61次中、小地震（3.0≤M≤5.5）和10次M≥6.0大地震的震源机制结果的统计分析,得到地震释能应力场的优势方向,主压应力轴为70°-80°,主张应力轴为340°-350°,它们的仰角基本上小于45°。这表明,华北地区处于以北东东向水平压应力和北北西向水平张应力为主的现代构造应力场中。指出了这一地区6级以上地震和震源深度大于17公里的中、小地震应力场方向一致性较好,可能更接近构造应力场方向。华北地区一致性应力场的南缘,可能在秦岭、大别山及长江下游一带。

DOMINANT DIRECTIONS OF STRESS FIELD FROM MINOR EARTHQUAKES IN NORTH-EASTERN CHINA

Based on the results of focal mechanism solutions and statistical analysis for 61 minor earthquakes （3.0≤M≤5.5） and 10 major earthquakes （M≥6.0） in northeastern China, the dominant directions of the earthquake generating stress field are found as follows:the directions of the compressive and tensile principal stress axes are NE 70°-80° and NW 10°-20°respectively, whereas the plunge angles are less than 45°. This shows that, in north-eastern China, the tectonic stress field is primarily represented by the NEE horizontal compressive stress and the NNW horizontal tensile stress. The stress field direction from major earthquakes and from minor earthquakes in depths more than 17 km appears to be closer to the direction of tectonic stress field. The southern ridge of the uniform stress field for north-eartern China probably lies in the zones of Chinling-Dabie Mountain and the lower reaches of the Yangtze River.