Relocation Of Mainshock And Aftershock Of The M_s7.0 Sichuan Jiuzhaigou Earthquake

After the earthquake,it is usually accompanied by a large number of aftershocks.The spatio-temporal spread of the after-seismic results of the aftershocks is helpful for explaining the fault-seismic fault structure and studying the relationship between faults and seismic activity.We review the classical location method and introduce the Source-specific station terms method.This method is simpler than the double-difference method,and is suitable for event catalogue with a lot of event.It is suitable for various single-event positioning based on travel time,and it is easy to parallel computing.On August 8,2017,an Ms7.0 earthquake occurred in Jiuzhaigou,Sichuan Province,China.A total of eight counties in Gansu and Sichuan provinces were seriously affected.The local people felt a strong earthquake,and there were many casualties.The continued aftershocks also had a profound impact on tourism.Jiuzhaigou area is located in the northeast margin of Bayankala Block in China,and near the epicenter there are Tazang fault,Minjiang fault and Huya fault,etc.In order to understand the distribution of the earthquake and its aftershock as well as the seismogenic fault structure,We study the Jiuzhaigou earthquake and its aftershocks using the Source-specific station terms method(SSST method).The results show that the Jiuzhaigou main shock is located at approximately 19 km depth,and the aftershocks are mainly distributed in the range of 5-15 km;compared with the results of single-event location method,the distribution of the aftershocks is more consistent with the linear character of faults strike,and more likely to have plane character;compared with the results of double-difference method,the spatial coverage of events could be wider.The results of relocation show that:the complete fault is the northwest extension of Huya fault;according to the distribution of aftershocks and correction terms in the study area,it is considered that the seismogenic fault should be divided into two sections,north and south;The length of aftershock area is approximately 40 km,the width of northwest section is approximately 10 km,and the width of southeast section is approximately 6.5 km.According to the distribution of aftershocks and the information of SSST items recorded at Jiuzhaigou station,the strike range of the fault is 144°?153°and the dip range is 63°?84°.