Source process of the 2010 Yushu, Qinghai, earthquake

The comprehensive waveform analysis of the Love waves and P waves shows that the Yushu M (S)7.1 (M (W)6.9) earthquake consists of two distinct sub-events. The first one occurred in the first 5 s releasing less seismic moment, and the second occurred in the later 11 s releasing more seismic moment. Spatially, the first sub-event surrounded the hypocenter, and the second, about 30 km away from the first, was much closer to the Yushu city and broke through the ground surface. In terms of the rupture velocity to which the peak values of the two sub-events correspond, the first sub-event propagated with an average rupture velocity of 1.6 km/s, however, the second propagated with an average rupture velocity of 4.0 km/s which is actually superior to the shear-wave velocity in the hypocentral region. The magnitude of the Yushu earthquake is in the lower margin of large earthquakes. The results obtained in this study indicate that the super-shear rupture possibly appears in earthquakes with magnitude of around 7.0, instead of only in the great earthquakes with magnitude around 8.0 [14, 15]. In addition, the energy focusing caused by the super-shear rupture should take key responsibility for the tremendous damage to the Yushu city as well as the ground-surface breakage related to the larger second sub-event.