川滇次级地块震源机制解类型与一致性参数

TYPES OF FOCAL MECHANISM SOLUTIONS AND PARA-METER CONSISTENCY OF THE SUB-BLOCKS IN SICHUAN AND YUNNAN PROVINCES

根据P波、S波的振幅并结合部分记录清晰的P波初动资料,求得1994—2005年川滇地区4个次级地块,即川青地块、雅江地块、川中地块和滇中地块2.5级以上有良好地震波记录的925次地震的震源机制解.结合已取得的中强地震的震源机制解资料,研究了上述4个次级地块的应力场特征及震源断层的错动类型.其P轴优势方位分布:川青地块为EW方向,雅江地块、川中地块、滇中地块为ESE或SE方位.根据大量震源机制解资料,编程计算了各地块的平均应力张量,即主应力σ1,σ2,σ3的方向.定义了单个震源机制解的力轴与平均应力张量的差异,或称震源机制解的一致性参数θ-,进而分析了川滇4个次级地块的-θ值和震源断层错动类型的分布及随时间的变化.通过次级地块大量区域小震震源机制解的测定,可以给出动态应力场和震源断层错动方式的变化信息.

Based on P- and S-wave amplitudes and some clear initial P wave motion, we calculated focal mechanism solutions of 928 M≥2. 5 earthquakes （1994-2005） in 4 subblocks of Sichuan and Yunnan Provinces, Combining these calculation results with those of the focal mechanism solutions of moderately strong earthquakes, we analyzed the stress field characteristics and dislocation types of seismogenic faults that are distributed in the 4 sub-blocks. The orientations of principal compressive stress are： 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 4 blocks. Meanwhile, we estimated the difference （also referred to as consistency parameter θ^-） between the force axis direction of focal mechanism solution and 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 de termination of focal mechanism solutions for each block, we present information on the variation in θ^-） value and dislocation types of seismogenic faults.