Study On The Interseismic And Coseismic Deformation Of The Northeastern Tibetan Plateau Based On Spatial Geodetic Data

Since the Cenozoic era,the collision and continuous pushing of the Indian plate to Eurasia at a rate of 36-40 mm/yr has made the Tibet Plateau rise to the highest altitude in the world and become one of the regions with the strongest lithosphere deformation in the world.The northeastern margin of the Tibet Plateau is the front edge area of the Tibetan Plateau extending into the mainland,and play a key role to understanding the mechanism of uplift and deformation of the Tibet Plateau.A thorough and detailed study on the structural deformation characteristics of the northeastern margin of the Tibet Plateau is not only helpful to clarify the uplift deformation mechanism of theTibet Plateau,but also of great significance to understand the process of continental strong earthquake preparation,continental dynamic evolution and plate tectonic theory.Based on the space geodesy(GNSS,InSAR),we simulated the interseismic and coseismic deformation in the northeastern margin of the Tibet Plateau.The results will greatly improve our understanding of some key issues including the structural deformation model,strain distribution mechanism and seismic risk in the northeastern margin of the Tibet Plateau.A total of 27 SAR data frames from four ascending and four descending of Sentinel-1 satellite spans from 2014 to 2021,were processed using SB AS time series analysis to obtain the LOS velocity field at the northeast Tibet Plateau over an area of nearly 720,000 km2.High-precision and high-resolution interseismic 3D velocity fields at the northeastern margin of the Tibetan Plateau in the Eurasian reference frame were aquired through velocity fusion with 270 GNSS stations within the SAR image coverage.The east-west velocity field is controlled by tectonic activity and is in good consistency with the major active faults,especially in the East Kunlun Fault Zone and the Haiyuan Fault Zone,which exhibit significant cross-fault velocity steps.The vertical velocity field is mainly controlled by factors other than tectonic activity,including subsidence in the Qilian Mountains permafrost zone,and possible subsidence due to groundwater extraction in several areas.Based on the obtained velocity field,the slip rate and its spatial variation characteristics of the East Kunlun fault from Tuosuo Lake segment to Maqin-Maqu segment and Qilian-Haiyuan fault are studied.The fault slip rate of the East Kunlun fault shows a non-monotonic decrease from Tuosuo Lake segment to the east,including Tuosuo Lake segment is 6.61～8.12 mm/yr,Tuosuo Lake-Anyemaqen Shan segment is 4.42～4.85 mm/yr,Anyemaqen Shan Extrusion Step Area is 2.72mm/yr and the Maqin-Maqu segment gradually decreases from 4.74～5.93 mm/yr eastward to 2.66 mm/yr.This decreasing slip rate may due to the adjusted by the mountain uplift of Anyemaqen Shan and the slip of the secondary fault on the south side of the East Kunlun fault.The postseismic effect of the 2001 Kokoxili Earthquake has negligible influence on the east of Tuosuo Lake along the East Kunlun fault.The slip rate of the Qilian-Haiyuan fault increases rapidly from 0.70 mm/yr to 3.58 mm/yr in the western of the Tuolaishan fault,3.84～4.11 mm/yr in the middle to eastern segment of theTuolaishan fault,3.10～4.66 mm/yr in the Lenglongling fault,4.99 mm/yr and 3.10 mm/yr in the Jinqianghe and Maomaoshan faults,respectively,3.15 mm/yr and 1.96 mm/yr in the western and eastern segment of the Laohushan fault,2.14 mm/yr and 2.47 mm/yr in the western and middle parts of the Haiyuan fault,respectively,and 0.67～2.52 mm/yr for the Gulang-xiangshan-Tianjingshan fault.The slip rate of Qilian-Haiyuan fault increases rapidly from the west segment of Tuolaishan fault to the east,and then,the slip rate is stable at 3～5 mm/yr until Laohushan segment.From Jinqianghe segment to the east,the slip rate gradually decreases,which may be decomposed into the slip on Gulang-Xiangshan-Tianjingshan fault.Based on the coseismic deformation field of the 2021 Madoi earthquake derived from GNSS and InSAR interferograms,we inverted for the slip distribution.The result showed that the Maduo earthquake was dominated by a left-lateral strike-slip.The coseismic rupture length on the main seismogenic fault is 170 km.The maximum slip was 4.4 m.The estimated total seismic moment is 1.61×1020 Nm,corresponding to a magnitude of Mw 7.4.The seismogenic fault is the Kunlun Pass-Jiangcuo fault.There are 4 asperities ruptured by the earthquake on the main segment,and the Maduo earthquake is an asymmetrically bilateral rapture event.The recurrence period of Maduo earthquake is 2200 years.The recurrence period of Menyuan earthquake is 833 years.The coseismic Coulomb stress changes shows that the stress on the Maqin segment of the East Kunlun fault was enhanced,indicating that there is the possibility of strong earthquakes in this region in the future.InSAR is used to obtain the coseismic deformation field of Menyuan earthquake from Sentinel-1 satellite images.The maximum displacements along the line of sight(LOS)are 0.75 m.Based on the co-registration of optically sensed images and correlation,the E-W coseismic deformation field was obtained from the multi-temporal Sentinel-2 data,and the maximum displacement was 2.5 m.Based on the coseismic deformation field derived from InSAR interferograms,we inverted for the slip distribution.The result showed that the Menyuan earthquake was dominated by a sinistral strike-slip.The coseismic rupture length on the seismogenic fault is 26 km.The maximum slip was 3.25 m.The estimated total seismic moment is 1.07×1019 Nm,corresponding to a magnitude of Mw 6.6.The seismogenic fault of the Menyuan earthquake is the Lenglongling fault,which caused the eastern segment of Tuolaishan fault to rupture.The coseismic Coulomb stress changes shows that the stress on the eastern segment of the Lenglongling fault and the western segment of the Tuolaishan fault was enhanced,implying that there is the possibility of strong earthquakes in this region in the future.