Abstract: On 13, April, 2010, a great earthquake of M_W7.0 occurred in Yushu County, Qinghai Province, which is another big one in China since 2008 Wenchuan earthquake. And with seismic wave data, InSAR data and field investigations, many researchers studied the focal mechanism and source rupture process of this earthquake and many valuable results were obtained. However, there are some arguments on the rupture velocity. Some think that this earthquake is a super-shear rupture event, and some insist on opposite opinion. In order to explore whether it is a super-shear rupture event or not, this study chooses the teleseismic wave data recorded by 33 seismic stations with epicentral distances between 30～90 degrees, good azimuth coverage and high signal-noise ratio to reexamine the rupture process using Yagi's program. By comparison of different given rupture velocities in the range of 2.5～5.5km/s, it is found that rupture velocity of 4.7km/s yields the smallest normalized misfit between the observed and synthetic waveforms. And the inversion result is more in accordance with field observation. The relationship between subfault dimension, rise time and rupture velocity is discussed, which shows that the rupture velocity is not so dependent on the two parameters. And by teleseisemic analyses using an envelope deconvolution method with an empirical Green's function, the location and timing of the high-frequency event also show a rupture velocity of 4.7 to 5.8km/s, which is apparently greater than the shear wave velocity in this region. By comprehensive analyses, it can be concluded that the super-shear rupture exists in this earthquake. According to our inversion result, the strike, dip, and rake angle of this earthquake separately is 300, 88 and 4. Beach ball shows the seismogenic fault is of strike-slip type, which is consistent with the Ganzi-Yushu Fault. And the rupture extended to the surface on the northwest and southeast segments of the Yushu Fault with the length of 19km and 31km. Due to the existence of pull-apart Longbao Basin, the central part where the epicenter is did not rupture. By comprehensive analysis, super shear rupture is one of the main reasons that caused serious damage to Yushu County.

Key words: source rupture process, super-shear rupture, high frequency P wave envelope

摘要： 为探讨玉树地震是否为超剪切破裂事件，利用Yagi的方法重新进行了此次地震震源破裂过程的反演。通过给定不同的破裂速度进行对比，发现当破裂速度为4.7km/s时，理论与实际观测结果拟合残差最小，且反演结果更符合实际。另据P波高频辐射能量包络反演，破裂传播速度在4.7～5.8km/s范围内，而该地区的剪切波速度则为3.0～3.6km/s，从而证明了此次地震超剪切破裂现象的存在。反演结果表明，此次地震在玉树段的NW和SE段形成了19和31km的地表破裂，而震中所在的中段由于隆宝湖拉分盆地的存在，造成了15km的未破裂区。超剪切破裂是造成SE段玉树县城遭受严重破坏的原因之一。

关键词: 震源破裂过程, 超剪切破裂, P波高频辐射能量包络