Present Crustal Deformation Characteristics In The Northeastern Tibetan Plateau Detected With Time-series InSAR

The Tibetan Plateau,roof of the world,is formed by the collision of the Indian plate and the Eurasian plate.Its formation and evolution is one of the greatest geological events in the history of the earth.The northeastern margin of the Tibetan Plateau is the convergence zone of the active Tibetan Plateau,the stable Alxa block,the stable Ordos block and the stable South China block.As the front part of the Tibetan Plateau extending into the mainland,the topography of the northeastern margin of the Tibetan Plateau is pretty complex,and its structural deformation is particularly significant with active seismic activities.It is of great scientific significance to explore the current crustal deformation characteristics of the northeastern margin of the Tibetan Plateau.In this study,we collected almost 3800 Sentinel-1 SAR images,which covered the northeastern margin of the Tibetan Plateau from October 2014 to October 2020.Combined PS-InSAR technique and GNSS velocity data in this area,we jointly calculated the current three-dimensional velocity field of this area.Then we used the three-dimensional block back-slip model provided by the Tdefnode program to acquire the slip rate and locking ratio of major fault zones,such as the Haiyuan fault,the Liupanshan fault,and the northern margin of west Qinling fault.We used different types of data to constrain the inversion model: a)GNSS horizontal velocity field,b)GNSS horizontal velocity and InSAR line-of-sight velocity,c)three-dimensional velocity field calculated by GNSS and InSAR,and compared their result.Furtherly,we analyzed the seismic risk.The main work and conclusions are as follows:(1)Collected about 3800 Sentinel-1 C-band SAR data covering the northeastern margin of the Tibetan Plateau from October 2014 to October 2020.Based on the open source software ISCE and Sta MPS,time-series interference processed to obtain the average line-of-sight deformation rate field and the PS point time series results in the study area.The GNSS velocity field was introduced to merge adjacent track and correct the slope trend to obtain a large-scale InSAR line-of-sight deformation rate field in the study area.The results show that most part of the study area is in a stable state,but it has clear velocity change crossing some segments of faults.(2)Combined the InSAR corrected line-of-sight deformation velocity field and the GNSS horizontal velocity field,the equations are constructed to perform least squares adjustment iteration to obtain the dense three-dimensional deformation field of the study area.The results show that,relative to the Ordos block,the vertical movement of the northeastern margin of the Tibetan Plateau is generally subtle,some mountains are uplifted,and the subsidence caused by non-structural(coal mining,groundwater mining,etc.)is widely distributed;the lithosphere of the study area moves northeast relative to the Ordos block,and there is a large-scale dextral shear;the deformation velocity difference between two sides of large faults in the region is much obvious.Through profile analysis of the three-dimensional deformation field in the study area,it can be seen that the Haiyuan earthquake rupture zone has a left-lateral strike-slip rate of about4mm/yr,which is in a postseismic deformation state,the Liupanshan fault is compressed and shortened at about 4mm/yr,and the northern margin of the West Qinling fault is left-handed,whose strike-slip rate is about 0.5mm/yr.(3)Using different data to constrain the inversion model,combined with the geometric kinematics parameters of the active fault in the study area,the negative dislocation model of faults was used to inversely simulates the three-dimensional distribution of the slip rate,locking ratio and slip deficit of the main fault zones.The results show that introducing InSAR data to inversion has improved its results.The inversion results of the three combined methods are relatively consistent.The middle section of the Baidunzi fault,the eastern section of the Haiyuan Fault Zone(Lenglongling-Jin Qianghe-Maomaoshan subsegment),the middle section of the Liupanshan fault,the middle section of the northern margin fault of the west qinling(Zhangxian-Wushan-Gangu subsegment)are in a locked state,and the seismic risk is much greater than other areas on the northeastern margin of the Tibetan Plateau.