Focal mechanisms and seismogenic structures of the M_s4.7、M_s7.1 and M_s6.3 Yushu earthquakes of April.14,2010

Based on digital broad-band seismic records of Qinghai,Xizang,Sichuan regional seismic network and CSN,we inversed the focal mechanisms and possible centroid depth of the M_S4.7 foreshock,M_S7.1 mainshock and M_S6.3 aftershock of the Apr 14,2010 Yushu earthquake sequences using the "Cut and Paste"(CAP) method,and analyzed the seismogenic structures combining with the distribution of active faults near the epicenter and filed investigation of surface rupture zone.The Results show that the earthquake surface rupture of the M_S7.1 mainshock is 129°,84°and 17°for strike,dip and rake angles,respectively,the centroid depth is about 6 km and the moment magnitude is 6.8;the earthquake surface rupture of the M_S4.7 foreshock is 114°,67°and-5°for strike,dip and rake angles,respectively,the centroid depth is about 11 km and the moment magnitude is 4.2;The earthquake rupture surface of the M_S6.3 strong aftershock is 123°,89°and 9°for strike,dip and rake angles,respectively,the centroid depth is about 6 km and the moment magnitude is 5.7.The seismogenic structure of the Yushu earthquake sequences is the Ganzi-Yushu-Fenghuoshan fault;the focal mechanism is mainly left lateral strike slip type.The strike of the source rupture plane is basically consistent with the general strike of surface rupture of the M7.1 mainshock.Comprehensive study on the source character of the foreshock-mainshock-strong aftershock indicates that the dip of the seismogenic structure in shallow is vertical and gradually becomes flat in the deep part