Abstract: The authors mainly analyzed the focal mechanism solution of small and moderate earthquakes, their system cluster and stress field inversion along middle-east segment of northern Tianshan region. The result shows that the rupture characteristics of small and moderate earthquakes in research area were mainly the inverse faulting in nature. The main fracture of earthquakes is basically distributed along NWW or near EW. It is consistent with the regional tectonic belt of NWW. In research area, the main compressional stress P axis is near NS, and the inclination angle is small. The inclination angle of the main tensile stress T axis is big. It indicates that the region stress field is mainly under action of the level extrusion of NS. The result of the stress field inversion in divisional area shows that, in middle and west part of research area, the maximum principal stress is near NS, and it is consistent with the tectonic stress field along western segment in northern Tianshan region.

Key words: Small and moderate earthquakes, Focal mechanism solution, System cluster, Inverse of stress field, Middle-eastern segment of northern Tianshan Range