Abstract: Through the method developed by Snoke, which uses the ratio of initial motion and amplitude of P, SV and SH waves, we calculated the focal mechanism solution to 83 M_L≥2.5 earthquakes since 2008 in eastern Qinling—Dabie region. Based on these focal mechanisms, we inverted direction characteristic of the mean stress field using the FMSI method. The result shows that Qinling—Dabie eastern region is horizontally compressed in nearly E-W direction and horizontally dilated in nearly N-S direction, which is in accord with statistical results of focal mechanism parameters. We analyzed the variation information of the mean stress field direction through the consistency parameter of focal mechanisms, and the result shows that the focal mechanisms show a process from change in disorder and deviation from the mean stress field, to change in order and tendency to the mean stress field, then to change in disorder and deviation from the mean stress field. Consistency parameter of focal mechanisms in the studied region was in a continuous low value state before the significant earthquakes. Moreover, we calculated the apparent stress of 93 M_L≥2.5 earthquakes since 2008 in Qinling—Dabie eastern region, and fitted the relationship between apparent stress and magnitude, analyzed the time variation characteristic of the difference apparent stress that eliminated the effect of magnitude and reflected the variation of stress magnitude in the study area. The result shows that apparent stress in studied region showed a distinct process of first rising and then decreasing before significant earthquakes, and the significant earthquakes occurred during the process of decreasing. Finally, we analyzed the stress state in the study region by using consistency parameter of focal mechanism and difference apparent stress, and the result showed that regional stress field enhanced apparently before significant earthquakes. At present, the consistency parameter of focal mechanism in the study area is high, and difference apparent stress is low, so the regional stress level is low.

Key words: Focal mechanism solution, Stress field, Apparent stress, Stress state, Qinling—Dabie eastern