The M_S7.1 Yushu earthquake surface rupture and large historical earthquakes on the Garzê-Yushu Fault

As revealed by field investigations,the co-seismic surface rupture zone of the 2010 MS7.1 Yushu earthquake,Qinghai is a characteristic sinistral strike-slip feature consisting of three distinct sinistral primary ruptures,with an overall strike of 310°-320° and a total length of 31 km.In addition,an approximately 2-km-long en-echelon tensile fissure zone was found east of Longbao Town;if this site is taken as the north end of the rupture zone,then the rupture had a total length of ～51 km.The surface rupture zone is composed of a series of fissures arranged in an en-echelon or alternating relationship between compressive bulges and tensile fissures,with a measured maximum horizontal displacement of 1.8 m.The surface rupture zone extends along the mapped Garze-Yushu Fault,which implicates it as the seismogenic fault for this earthquake.Historically,a few earthquakes with a magnitude of about 7 have occurred along the fault,and additionally traces of paleoearthquakes are evident that characterize the short-period recurrence interval of large earthquakes here.Similar to the seismogenic process of the 2008 Wenchuan earthquake,the Yushu earthquake is also due to the stress accumulation and release on the block boundaries resulting from the eastward expansion of Qinghai-Tibet Plateau.However,in contrast with the Wenchuan earthquake,the Yushu earthquake had a sinistral strike-slip mechanism resulting from the uneven eastward extrusion of the Baryan Har and Sichuan-Yunnan fault blocks.