用P波、S波初动和振幅比计算中小地震震源机制在云南地区的应用

THE APPLICATION OF FOCAL MECHANISM DETERMINATIONS OF MODERATE-SMALL EARTHQUAKES IN YUNNAN PROVINCE USING THE FIRST MOTION AND AMPLITUDE RATIO OF P AND S WAVE

利用云南数字地震台网记录的区域波形资料，用P、S波初动和P、S波的振幅比联合计算了发生在云南省内的91次中小地震的震源机制。通过与矩心矩张量法和P波初动法的结果对比分析，认为用P、S波初动和振幅比求解震源机制的方法是可行可靠的，用这种方法不仅可以得到5级以上地震的震源机制，也可以计算台网分布较好地区的3—4级地震的震源机制。另外，用91个地震的震源机制资料得到了云南地区震源机制类型、主压应力轴的平面分布及其统计图，结果表明云南地区以走滑型地震为主，主压应力轴优势分布方向为NNE向，这些结果与利用哈佛得到的结果是一致的。

In this paper,focal mechanisms of 91 moderate-small earthquakes occurred in Yunnan are calculated using digital seismic wave data from Yunnan digital seismic network based on the program of focal mechanism determinations combing the first motion of P, SV and SH waves with their amplitude ratio. Compared with the results using centroid-moment-tensor and first motion of P wave, our result is more reasonable. The method can not only be used to calculate focal mechanisms of earthquakes bigger than ML5.0, but also can be used to calculate focal mechanisms of moderate-small earthquakes. Additionally, the focal mechanisms types ,horizontal distribution and statistical diagram of maximum stress orientations in Yunnan has been calculated using focal mechanisms of 91 moderate-small earthquakes, the results show that the focal mechanisms are mainly slip faulting and orientations of maximum stress mostly are in the NNE direction in Yunnan, which are accordant with the results using Harvard data.