会泽5·3级和文山5·3级地震序列震源参数研究

Study on the Source Parameters of the Huize M_S5.3 and Wenshan M_S5.3 Earthquake Sequences in 2005

利用云南区域地震数字台网记录到的2005年8月5日云南会泽Ms5．3地震和8月13日文山Ms5．3地震的数字地震波形记录，在对S波观测记录位移谱进行传播路径、场地响应和仪器响应等校正后，根据Brune圆盘震源模型，利用遗传算法估算了这两个地震序列的震源参数。结果表明，两个序列的地震矩M0均在10^12-10^14N·m之间，与近震震级有很好的线性关系，与震源半径呈线性关系；应力降与近震震级无明显的依赖关系；拐角频率和地震矩之间有明显的依赖关系，但拐角频率的实际计算值fc与在给定地震矩条件下得到的估计值fa之差及应力降随时间的变化表现出了不同的特征：会泽地震序列的拐角频率差值和应力降在ML3.1余震前有一个由高到低的变化过程，反映了余震区应力场增高一下降的过程；文山地震序列拐角频率差值和应力降在ML≥3．1余震前均会出现高值或低值异常。

On August 5 and 13,2005 respectively occurred the Huize Ms5.3 and Wenshan Ms5.3 earthquakes in Yunnan. The Yunnan Regional Digital Seismic Network recorded them. By removing propagation, site and instrument effects from the displacement spectra of the S-wave recordings, we obtain the source parameters of the Huize and Wenshan earthquake sequences based on the Brune disc model and Genetic algorithm, namely, the seismic moment M0, stress drop Ao- and comer frequency ft. The results show that there is a good linear relation between M0 （10^12-10^14 N · m） and local magnitude ML; between M0 and rupture radius r is also a linear correlation; Ao- seems independent on ML; fc increases with M0 decreasing. According to the fc-Mo relation, we can give estimated comer frequency fo. As for the two earthquake sequences, their comer frequency differences （fc- fa ） and stress drops vary with time differently. The Huize earthquake sequence shows the change from high value to low value before the aftershocks with ML ≥3.1, which reflects the process of the stress field in the aftershock region varying from increase to decrease; whereas, the Wenshan earthquake sequence has the feature of high value or low value before the aftershocks with ML ≥3.1.