Analysis Of Seismogenic Structure And Genetic Mechanism Of Ms7.0 Earthquake In Jiuzhaigou,Sichuan

At 8:19:46 on August 8,2017,a magnitude 7.0 earthquake occurred in Jiuzhaigou County,Aba Prefecture,northern Sichuan Province.The Jiuzhaigou earthquake is the third major earthquake that occurred in the active tectonic belt on the eastern edge of the Bayan Hara block in the past decade.The other two were the 2008 Wenchuan M8.0earthquake and the 2013 Lushan M7.0 earthquake.The field investigation did not find obvious co-seismic surface rupture,so there is no unified understanding of the seismogenic fault and the genetic mechanism of the Jiuzhaigou earthquake.Based on field investigation,this paper studies the seismogenic fault and genetic mechanism of the Jiuzhaigou earthquake,by comprehensively analysing the coseismic deformation field and seismic fracture geometric parameters acquired by InSAR technology,remote sensing data,coseismic landslide distribution data,historical seismic data,and predecessor data.This paper mainly gets the following points:1.Based on the Sentine-l radar image data,the co-seismic deformation field of the Jiuzhaigou 7.0 earthquake in 2017 was obtained by D-InSAR technology,and the fault sliding distribution was inverted.The results show that:?1?the maximum lift of LOS is15.2 cm and the maximum settlement is 21.0 cm.?2?the maximum slip of the earthquake is 1.06 m,the total moment of earthquake release is about 6.82×10¹⁸ Nm,and the magnitude of the moment is Mw6.46;?3?the seismogenic fault of Jiuzhaigou earthquake is the northern segment of the Huya fault.2.Based on the combination of field geological survey and remote sensing interpretation,the distribution characteristics of the coseismic landslides in Jiuzhaigou earthquake are analyzed.The results show that?1?there are two coseismic landslide-intensive development areas in the earthquake zone,and the distribution characteristics of the landslides are in good agreement with the distribution of the seismogenic faults;?2?The distribution of the earthquake-induced landslides in Jiuzhaigou earthquake has obvious fault effects,including distance effect,direction and slope effect,and intensity effect.3.Comprehensive analysis of historical seismic data,geophysical data,InSAR inversion results,characteristics of Huya fault and kinematic characteristics of Bayan Har block,this paper believes that the occurrence of the Jiuzhaigou earthquake is related to three types of seismogenic conditions:?1?the northern section of the Huya fault is a fault section?seismic empty area?where no rupture occurs,which is the background conditions for a major earthquake.?2?The Huya fault with a high dip angle is a left-lateral strike-slip fault,which is the fault condition for the Jiuzhaigou earthquake;?3?The lower crust flow is the dynamic condition for the earthquake in Jiuzhaigou.Driven by the lower crust flow,the Bayan Har block interacts with the South China block,causing the northeast corner of the Bayan Har block to be extruded in the northeast direction.In the process,it is blocked by the Qinling Mountains,causing the Huya fault to become stress concentration area.