Surface rupture characteristics,rupture mechanics,and rupture process of the Yushu earthquake(Ms7.1),14/04/2010

On 14 April 2010,an earthquake(Ms7.1) happened in the Yushu region,Qinghai Province,causing large casualties and property losses.After the earthquake,we carried out a detailed investigation of the earthquake surface rupture zone,and accurately measured co-seismic displacements.Based on our field investigation and measurements,the characteristics of the Yushu earthquake surface ruptures and coseismic displacements and their distribution pattern were analyzed.The earthquake rupture mechanism and the rupture process were discussed.According to our research,the following understandings were obtained:(1) The Yushu earthquake produced two surface ruptures along the northwest section of the Xianshuihe fault(Ganzi-Yushu fault).The western surface rupture is located in the Longbao lake pull-apart basin near the micro-epicenter,and is about 19km long.The eastern surface rupture is located along the hillsides south of Zhaqu river and the west of the Batang river,and is about 31km long.There is a ～15km gap between the former two segments of the surface rupture zone.(2) Field measurements show that the maximum coseismic displacement for the Yushu earthquake is 2.3m,located at the center of the eastern surface rupture,near the Guoyangyansongduo village.(3) The characteristics of the surface rupture as well as field tectonic geomorphology indicate that the ruptured fault is developed in transtensional setting.Tension normal fault developed during the sinistral strike-slip process of the fault.(4) Seismic data invertion result and the distribution of the surface rupture show that the Yushu earthquake consist of two sub-events,which formed the Longbao lake surface rupture zone and Zhaqu river-Batang river surface rupture zone,respectively.The valley west of Yushu City and the Longbao Lake are both pull-apart basins formed during the transtension activity of the fault.