| Known as the "roof of the world" because of the collision of the Indian and Eurasian plates,the Tibetan Plateau has long been the focus of geologists’ attention and exploration.The study of deformation characteristics and mechanisms in and around the Tibetan Plateau is of great scientific significance for understanding the motion characteristics of related faults and the characteristics of seismic periodic deformation.The rapid development of Interferometric Synthetic Aperture Radar(InSAR)and abundant SAR image data provide important support for the deformation characteristics and the movement mode of faults in the peripheral region of the Qinghai-Tibet Plateau.In this paper,the Sentinel-1A SAR image data and InSAR technology are used to study the deformation characteristics and deformation mechanism of typical earthquakes in and around the Tibetan Plateau.The main research work and achievements are as follows:(1)On July 23,2020,a Mw6.3 earthquake occurred in Nyima region of Tibet,located in the central Qiangtang Block.Aiming at the atmospheric errors in the conventional differential InSAR co-seismic deformation field,this paper proposed a method of weighted superposition of multiple co-seismic interferogram to weaken the atmospheric errors.In other words,the multi-view Sentinel-1A orbital ascent and descent data from July to December 2020 were used.The Generic Atmospheric Correction Online Service for InSAR(GACOS)was used to remove some atmospheric influences,and the weighted superposition calculation of multiple co-seismic deformation fields after atmospheric correction was carried out.The results show that:The maximum line-of-sight displacements in the co-seismic deformation field of the ascending and descending rails are 0.31m and 0.24m,respectively.The multi-interferogram weighted average method can effectively improve the accuracy of the co-seismic deformation field,and the accuracy of the rise and fall of the orbit in the non-deformation area far away from the source area is increased by 44%and 52%,respectively.It can be seen that the multi-interferogram averaging method plays an important role in obtaining the reliable co-seismic deformation field of Nima earthquakes.(2)The Mw 6.6 earthquake occurred on January 8,2022 in Qinghai Gate,which is located in the northeastern margin of the Qinghai-Tibet Plateau.The occurrence of the earthquake is very important for the study of fault movement characteristics in this area.We obtained the interseismic and co-seismic deformation fields of the 2022 earthquake using the Sentinel-1A satellite SAR images from 2019-2021.We further estimated the slip rate,coupling depth and co-seismic slip model of the seismo-induced fault,and analyzed the motion characteristics of the seismo-induced fault.The results show that:1)the fault is mainly sinistral strike-slip,and the maximum displacement of the line-of-sight co-seismic deformation field observed by InSAR reaches 50cm;2)The fault that caused the 2022 event rupted the middle part of the Qilian-Haiyuan fault(LLLF)with a strike of 108.0° and a dip Angle of 83.6°.The slip was concentrated at a depth of 20km and above,with a maximum slip momentum of 2.3m.3)The pre-seismic fault is strongly locked,the fault slip rate between gate source earthquakes is 7mm/yr,the locking depth is 21.49km,and the locking depth is high.The earthquake released the deformation accumulation of about 300 years,and these characteristics are closely related to the occurrence of strong earthquakes.(3)The source mechanism of the February 23,2023 Tajikistan Mw6.8 earthquake given by different institutions is quite different,which is still controversial.In order to better understand the surface deformation pattern and source characteristics of the earthquake,the co-seismic deformation field was obtained by using Sentry No.1 data of the raised and lowered orbit based on the traditional two-track differential interferometric synthetic aperture radar(InSAR)technology.Through nonlinear and linear model inversion,the co-seismic source model of this earthquake is obtained,and the possible coulomb failure stress(CFS)migration is further analyzed.The results show that:1)The earthquake ruptured a left-side blind strike-slip fault with a strike of 28.1°,with a maximum slip of 1.53m and a geodetic seismic moment of 1.99×1019N·m(Mw6.83).2)The seismogenic fault is the secondary fault of Sarez-Karakul fault;3)The 2015 Mw 7.2 earthquake in Sarez may have acted as a trigger for the 2023 Tajikistan earthquake.The seismic risk of the Sarez-Karakul fault system and the Sarez-Murghab thrust system is enhanced due to the Coulomb stress of the earthquake loading in Tajikistan. |
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