2013年8月12日西藏昌都地区左贡县、芒康县交界发生6.1级地震，地震序列为前-主-余型，在主震发生前9h内发生了7次ML≥2.0中小地震，最大震级为ML4.7。本文采用体波谱振幅相关系数方法，基于区域测震台网记录的数字地震波形资料研究左贡－芒康6.1级地震序列震源机制变化过程。结果显示，主震前的中小地震相关系数较高，均值为0. 86，表明其震源机制相似程度较高，是具有震兆意义的小震序列;余震的相关系数较低，表明震源机制相似程度较低。

The MS6.1 earthquake is foreshock-mainshock-aftershock type which happened in boundary region between Zogang and Markam counties on August 12，2013． Within 9 hours before the main shock seven times more than the ML2． 0 earthquake occurred，in which the maximum magnitude is ML4． 7． In this paper，the earthquake focal mechanism changing process of Zogang-Markam MS6． 1 earthquake sequence is studied by calculating correlation coefficient of body wave spectral amplitudes，and the result shows that the correlation coefficients of spectral amplitude of foreshocks present high value fluctuation，the average value is 0． 86，what shows that the focal mechanism of foreshocks are similar; and the correlation coefficients of spectral amplitude of aftershocks present low value，what shows that the possibility of a large earthquake is not high after time．

四川省地震局地震科技专项项目(LY1302)、国家科技支撑计划项目(2012BAK19B02)共同资助