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

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.