Study On The Fault Rupture And Seismogenic Structure Of NIMA Earthquake In 2020 Based On InSAR Technology

The continuous collision and extrusion between the Indian and Eurasian plates led to the intense deformation and uplift of the Tibet plateau.It is precisely because of this continuous inter-plate interaction that the Tibet has become one of the regions with high frequency,wide distribution and frequent strong earthquakes in the world.Studying the causes of small earthquakes in the Tibet is of great significance for understanding the deformation mechanism of the Tibet and monitoring the current state of motion,meanwhile it provides a research basis and enlightenment for studying the causes of earthquakes in the Tibet rift.On July 23,2020,an Mw6.3 earthquake occurred in Rongma Nima County,Naqu City,located in the northern Tibet Plateau.We processed the Sentinal-1 SAR data of the ascending and descending track covering the earthquake area were obtained from ESA with D-In SAR technology.It is found that the deformation field is dominated by subsidence: the maximum subsidence in the LOS direction of the 12 track is ～29cm and the maximum uplift is ～9cm;the maximum subsidence of the 121 track is ～27cm and the maximum uplift is ～2cm;the maximum subsidence of the 19 track is ～27cm and the maximum uplift is ～2cm.In order to further analyze the characteristics of the coseismic deformation field of the Nima earthquake,we based on the deformation field data of the 12 track and the 121 track,ignored the north-south deformation,the threedimensional deformation field of the Nima earthquake was solved,then it was found that the three-dimensional deformation field of the Nima earthquake was dominated by subsidence.The maximum settlement is about 37 cm.The Bayesian method is used to establish a uniform fault model to invert the geometric parameters of the seismic fault.Then,based on the fault geometry parameters obtained by the uniform fault model,the distributed fault model was established by using two sampling methods of uniform and quad tree,and the fine sliding distribution of two different tendencies of seismic faults was inverted.From the perspective of data fitting,the fault geometry of the Nima earthquake cannot be inverted by relying solely on In SAR measurements.The coulomb stress disturbance of the 2008 change earthquake on the 2020 Nima earthquake was analyzed,and it was found that from the perspective of stress triggering,the Gaize earthquake did not cause an impact on the Nima earthquake.Based on the established fault model,the special seismic structure of Nima was analyzed,which is a shallow source earthquake that occurs in the special geological structure of the graben,then causing the overall subsidence of the Yibuchaka graben.By analyzing the dynamic environment of the Nima earthquake,it is believed that the Nima earthquake is a stress accumulation in the Step-over band between the two sinistral strike-slip of the Yibuchaka-Riganpeicuo fault and the Jiangaizangbu fault,then under the background of east-west stretching and north-south extrusion of the Tibet Plateau,a stress release event related to graben activity is generated because of the long-term stress accumulation.The effect of Nima earthquake on regional fault stress disturbance was analyzed,and the results showed that Nima earthquake had unloading stress on regional faults.