Study On The Present-day Tectonic Activity Of Jiagang-dinggye Rift In Southern Tibet By Using GPS&InSAR

Due to the collsion of the Indian plate with the Eurasian plate,there are many unique tectonic features in the south Tibet,and the most representative one is the north-south tensile rift,which is closely related to the uplift of the Tibet,block movement and earthquake.However,due to the lack of geodetic survey and geological data,the role of rift zone in geological structure in the south Tibet is still limited.This paper take the Jiagang-Dinggye as the breaking point and combined with InSAR and GPS data to determine the seismic risk,locking depth,slip rate of this fault and the rotation speed and movement speed of the adjacent blocks,so as to explore the structural characteristics of the south Tibet region.The Xietongmen earthquake of Mw5.8 and the Dingri earthquake of Mw5.7occurred on the north and south sides of the Jiagang-Dinggye fault on December 24,2018 and March 20,2020,respectively.Due to the lack of near field data,the location of the epicenter of the earthquake and the seismogenic fault are still controversial.This paper uses the Sentinel-1 satellite orbit data to obtain the coseismic deformation field,and invert the coseismic slip distribution model of two earthquakes based on the homogeneous elastic half-space model.The seismogenic fault and earthquake risk are discussed.After that,taking the occurrence of Jiagang-Dinggye fault obtained as a reference,this paper takes the south Tibet's five north-south fault(the Palongcuo fault,the Longgeer fault,the Nima-Dingri fault,the Jiagang-Dinggye fault and the Yadong-Gulu fault)and the east-west Yarlung Zangbo suture zone as the object,divides the south Tibet into 10 blocks,uses the calculated GPS velocity data,based on the negative dislocation model inversion method,combined with the geological structure and previous studies,discusses the Jiagang-Dinggye and the South Tibet's structural characteristics.The conclusions are as follows:(1)The model shows that the average slip angle of two earthquake are close to-90°,indicating that two earthquakes are typical normal slip event.The main slip of the Xietongmeng earthquake is located within the depth range of 2-12 km,with the average slip of 0.02 m,the maximum slip of 0.10m,the focal depth of 6.58 km and the moment released about 5.056×10¹⁷Nm,corresponding to a magnitude of Mw5.7;The main slip of the Dingri earthquake is located within the depth range of 2-9 km,with the average slip of 0.03m,the maximum slip of 0.29m,the focal depth of 4.50km and the moment released about 6.751×10¹⁷ Nm,corresponding to a magnitude of Mw5.81.Based on the location of the epicenter and the slip mechanism of both earthquakes,we believe that the Jiagang-Dinggye fault's branch fault is the seismogenic fault.Furtherly,The seismic risk of the Xietongmen earthquake is discussed on the basis of historical earthquake statistics and stress analysis.(2)The studies find that the locking depth of the Jiagang-Dinggye's north section and the south section are 16km and 9km,respectively.In terms of slip rate,the five north-south faults in southern Tibet shows sinistral strike-slip and extension,and the extension in the southern segment is greater than that in the northern segment,while the Yarlung Zangbo suture zone shows destral strike slip and shortening.The overall extension rate of the Jiagang-Dinggye fault is 3mm/yr(the extension in the northern segment is 2.1mm/yr,the extension in the southern segment is 3.9mm/yr).Besides,the block rotation of the block(Block between the northern segment of the Jiagang-Dinggye fault and the the northern segment of the Nima-Dingri fault)and block,(Two blocks between the Yadong-Gulu fault and the Cuona-Qiongjie fault)have the highest rotation speeds,which are-2.166±0.247°/Ma,-2.765±0.062°/Ma,-2.004±0.028°/Ma,respectively,and the rest blocks are 0.2-0.7°/Ma.The block velocity are all about 20-30mm/yr,showing a north-east direction and gradually shifting from west to east,and the block velocity in the south of the Yarlung Zangbo suture zone is generally higher than that in the north.