A new technique for moment tensor inversion with applications to the 2008 Wenchuan M S8.0 earthquake sequence

A M _S8.0 earthquake occurred in Wenchuan County, Sichuan Province, China, 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 seven larger aftershocks (M _S5.0∼6.0) by a new technique of moment tensor inversion using the broadband and long-period seismic waveform data from the Global Seismic 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 real procedure for inverting the moment tensor; secondly, the moment tensor solutions and STFs of the eight 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 the new approach is efficient and feasible. By using this approach, 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 the most of the aftershocks occurred in the main faults of the Longmenshan fault zone with predominantly thrustingwith 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. Contribution No. 08FE3006, Institute of Geophysics, China Earthquake Administration.