中文摘要：

本文提出了一种基于恒定破裂速度和固定子事件震源时间函数的假定、利用远场地震波形资料获取大地震震源机制的时空变化图像的线性反演方法，并利用这种方法及全球范围内48个台站的长周期波形资料反演建立了2008年汶川Ms8．0地震的震源机制随时间和空间变化的图像．根据这个图像可知，汶川大地震断层的西南端震源机制接近于逆冲，随着破裂向东北方向延伸，震源机制的走滑分量逐渐增大，走滑分量超过逆冲分量的转折点在震中东北大约190km的位置．为了检验反演方法的有效性和反演结果的可靠性，我们特别设计了一个数值试验对反演结果进行了检验．检验结果表明，我们在本文中提出的反演方法是有效的，关于汶川大地震的反演结果也是可靠的（除长周期信号较弱的一段外）．通过比较发现，反演结果与震后野外考察的结果也相当吻合．

英文摘要：

A linear inversion technique based on assumption of constant rupture velocity and fixed source time functions of sub-events is proposed in this paper for inverting teleseismic waveform data to image spatio-temporal variation of source mechanism of large earthquakes, and applied to the 2008 Wenchuan Ms8. 0 earthquake, obtaining its image of the spatio-temporal variation of source mechanism by inverting 48 worldwide stations of long period waveform data. The image shows that the mainly thrust mechanism appeared in the southwest segment of the fault, and the strike-slip component was getting more and more with the fault extending northeastwards, with the turning point at which the strike-slip component became larger than the thrust-slip component appearing around 190 km northeast to the epicenter. In order to inspect the validity of the used method and reliability of the inverted results a specially designed numerical test was performed. The inspection indicated that the inversion method proposed in this paper was valid and the inverted results regarding the great Wenchuan earthquake were trustable （except those on one segment where the long-period component is weak）. A comparison shows that the inverted results were coincident with the field-investigation results.