一种矩张量反演新方法及其对2008年汶川M_S8.0地震序列的应用

A new technique for moment tensor inversion with applications to the 2008 Wenchuan M_S8.0 earthquake sequence

本文利用全球地震台网(GSN)的宽频带与长周期地震波形资料,采用矩张量反演的新方法,反演得到了2008年5月12日四川省汶川县MS8.0地震及其7个较大余震(MS5.0—6.0)的矩张量解与震源时间函数等震源参数.文章首先简要叙述矩张量反演新方法的理论背景和技术途径,并以汶川大地震的一个余震为例阐述了具体的实现过程;然后给出包括主震在内的8次地震的矩张量解和震源时间函数;最后分析探讨这些结果的构造意义.本文提出的矩张量反演新方法,不但与全球矩心矩张量(GCMT)一样,可以给出点源矩张量解,而且还可以给出点源的震源时间函数.反演得到的汶川大地震的7个较大余震的震源时间函数表明,即使是中等强度的地震也可能有复杂的震源过程;汶川大地震的多数余震发生在以逆冲为主、兼具小量走滑分量的龙门山断裂带的主断裂上,但很可能有些余震则发生在主断裂附近的次级走滑断裂上.

A Ms8.0 earthquake occurred in Wenchuan County, Sichuan Prov ince, on May 12, 2008, and subsequently, numerous aftershocks followed. We obtained the moment tensor solutions and source time functions （STFs） for the Wenchuan earthquake and its 7 larger aftershocks （Ms5.0 6.0） by a new technique of moment tensor inversion using the broadband and long-period seismic waveform data from the Global Seismographic Network （GSN）. Firstly, the theoretical background and technical flow of the new technique was briefly introduced, and an aftershock of the Wenchuan earthquake sequence was employed to illustrate the practical procedure for inverting the moment tensor; then, the moment tensor solutions and STFs of the 8 events, including the main shock, were presented; and finally, the interpretation of the results was made. The agreement of our results with the GCMT results indicates that the new technique is efficient and feasible. By using this technique, not only the moment tensor solution can be obtained but also the STF can be retrieved; the inverted STFs indicate that the source rupture process may be complicated even for the moderate earthquakes. The inverted focal mechanisms of the Wenchuan earthquake sequence show that most of the aftershocks occurred in the main faults of the Longmenshan Fault Zone with predominantly thrusting with minor right-lateral strike-slip component, but some of them may have occurred in the subfaults with strike-slip faulting in the vicinity of the main faults.