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Based on P- and S-wave amplitudes and some clear initial P-wave motion data, we calculated focal mechanism solutions of 928 M≥2.5 earthquakes (1994~2005) in four sub-blocks of Sichuan and Yunnan Provinces, namely Sichuan-Qinghai, Yajiang, Central Sichuan and Central Yunnan blocks. Combining these calculation results with those of the focal mechanism solutions of moderately strong earthquakes, we analyzed the stress field characteris-tics and dislocation types of seismogenic faults that are distributed in the four sub-blocks. The orientation of prin-cipal compressive stress for each block is: EW in Sichuan-Qinghai, ESE or SE in Yajiang, Central Sichuan and Central Yunnan blocks. Based on a great deal of focal mechanism data, we designed a program and calculated the directions of the principal stress tensors, σ1, σ2 and σ3, for the four blocks. Meanwhile, we estimated the difference (also referred to as consistency parameter θ ) between the force axis direction of focal mechanism solution and the direction of the mean stress tensor of each block. Then we further analyzed the variation of θ versus time and the dislocation types of seismogenic faults. Through determination of focal mechanism solutions for each block, we present information on the variation in θ value and dislocation types of seismogenic faults.
Based on P- and S-wave amplitudes and some clear initial P-wave motion data, we calculated focal mechanism solutions of 928 M ≧ 2.5 earthquakes (1994 ~ 2005) in four sub-blocks of Sichuan and Yunnan Provinces, namely Sichuan-Qinghai , Yajiang, Central Sichuan and Central Yunnan blocks. Combining these calculation results with those of the focal mechanism solutions of moderately strong earthquakes, we analyzed the stress field characteris-tics and dislocation types of seismogenic faults that are distributed in the four sub-blocks. The orientation of prin-cipal compressive stress for each block is: EW in Sichuan-Qinghai, ESE or SE in Yajiang, Central Sichuan and Central Yunnan blocks. Based on a great deal of focal mechanism data, we designed a program and calculated directions of the principal stress tensors, σ1, σ2 and σ3, for the four blocks. Meanwhile, we estimated the difference (also referred to as consistency parameter θ) between the force axis direction of the focal mechanism s olution and the direction of the mean stress tensor of each block. Then we further analyzed the variation of θ versus time and the dislocation types of seismogenic faults. Through determination of focal mechanism solutions for each block, we present information on the variation in θ value and dislocation types of seismogenic faults.