中文摘要：

已有研究表明，与一般性小震群相比，前震序列的震源机制更趋于一致．鉴于小地震的震源机制不易求解，本文利用谱振幅相关分析法研究小地震震源机制是否相似的问题，以探讨小震群序列类型判定的可能性．选择小震群活动频繁的云南西北部作为研究区域，计算发生在该地区的五个震群的谱振幅相关系数．结果显示，2001年施甸Ms5．9级及2001年永胜Ms6．0级强震震前的小震群序列谱振幅相关系数平均值分别为0．88、0．93；2002年漾濞、2003年洱源、2005年宾川三个一般性小震群的谱振幅相关系数平均值分别为0．48、0．68和0．63．表明，强震前的小震群序列与一般性小震群序列相比，谱振幅相关系数明显较大，接近于1．0，说明其震源机制相似性更为显著．本文针对小震群类型判定所作的理论推测与所研究震例实测结果基本相符合，初步表明，谱振幅相关分析法可能是判定小震群类型的物理意义较为明确的方法，具有实用价值，值得进一步深入研究．

英文摘要：

Study shows that the focal mechanisms of foreshock sequence are more consistent than those of general small earthquake swarm. Due to the intricacy of calculating the focal mechanism of small earthquakes, we use correlation coefficient of spectral amplitude to study the consistency of focal mechanism of small earthquakes, so as to analyze the possibility of determining the type of small earthquake swarm. We apply the method to five earthquake swarms in the northwest of Yunnan Province where small earthquake occurs frequently. The results show that the mean correlation coefficient of spectral amplitude of foreshocks of the Shidian MsS. 9 earthquake in 2001 is 0.88, the Yongsheng Ms6.0 earthquake in 2001 is 0.93, while the general small earthquake swarms in Yangbi （2002）, Eryuan （2003）, Binchuan （2005） is 0.48, 0.68, and 0.63 respectively. Theresults suggest that the correlation coetticient ot spectral amplitude ot toreshock sequence is larger, closer to 1.0 than that of general small earthquake swarm, which leads to more similarity of focal mechanisms of foreshock sequence. In this paper, the theoretical expectations conform to the actual calculated results in these earthquake cases. This feature preliminarily implies that the correlation analysis of spectral amplitude could serve as a method that has clear physical significance and practical utility in determining the type of the earthquake swarm, and thus be worthy of further study.