A Study On Crustal Deformation Based On GPS Data In The Northeastern Margin Of The Qinghai-Tibetan Plateau

The study on the deformation of the Qinghai-Tibatan Plateau show thatnorth-south compression and crustl thicking in the vertical existsreally. It shows that driven by the northward indentation of the Indianplate, it is not assured that the deformation of a lots large-scalestrike-slip faults and plates in the Tibetan plateau and its vicinityareas is dominant.The northeastern margin of the Qinghai-Tibetan Plateau is the frontposition of the whole plateau,this area developed several large scaleactive tectonics which are very active durying the last Quaternary.Because the tectonic deformation of the faults are very complicated, itis not assured that the contemporary slip rates and methods in some faults.The key reason is how to make certain the slip rates.the difference theabove-mentioned prove will decide the slip rates in the inner of thePlateau and the shortening rates. If there is hundreds of kilometres slipnumber, it will prove that "the extrusion of the continent"is dominant.Whereas ,the crustal thicking will do.In the last decade GPS technology has gained rapid development, manyobeservations and researches have been done by lots of departmets in thisarea. As one of them, "Crustal Movement Observation Network of China",has about 260 GPS stations with three peroidic observationdata(1999,2001,2004). All of these data are good constraints to inverseand acquire the slid rates of the main active faults.In this paper, 3-D geometric model in sections was establishedaccording to the previous geological and geophysical achievements. Andthen, the reliable and quantitative crust movement speed is acquiredbased on the data which comes from "Crustal Movement Observation Networkof China". In this way, we take the previous slide speed of the faultsections which is reliable as known information to application, use 3-Ddeep-fault dislocation model which fits the local GPS speed field toinverse the slide speed of the other fault nowadays. Furthermore, as forthese questionable slide speed of these faults which are not very activeor small scale, we get more detail slide speed of the inversion faults.In the end, the dynamic mechanism of the crust deformation reasons isdicussed through the ANSYS software on the basis of the GPS data.The work and conclusions fo this work are as follows:1. Based on date of the main active faults in the the northern marginof Tibet Plateau firstly, the three-dimensional geometric model "thedistribution of faults" is established;then with the constraint of thesliding speeds in some faults studied thoroughly, on the basis of about"Crustal Movement Observation Network of China"260 GPS stationsthrough the northern margin of Tibet plateau. the dense GPS velocityfield will be given with the" three-dimensional deep dislocationmodel". Then the velocity field of the Qinghai-Tibetan Plateau will begotten by the "Three-dimensional Deep Dislocation Model"。At the sametime,the sliding rate and thrusting rate will be given.2. Contrasted with the results given by Xuxiwei,the results gottenby the Altyn Tagh fault system team of China Earthquake Administrationare in accordance with the results gotten by "three-dimensional deepdislocation model" based on GPS data . The results show that there is2.15±2.3mm/a left-lateral slip . For middle of the faults, there is5.16±2.1mm/a thrusting rates in the segment of Heshanpu-Xiangshuihe .there is 4.36±2.1mm/a thrusting rates in the segment ofXiangshuigou-Sanzhuangzi. The results are in accord with the resultgiven by Dengqidong and far larger than the results given byXianghongfa who think that the left-lateral slip rates is 1～3mm/a innorth of the faults. There is 0.89mm/a thrusting rates in middle and southof the faults. For the North Margin of the Riyueshan faults, the ElashanFaults, the results gotten by the inversion are in accordance with thegeological results.3. On the basis of 12 GPS stations data through the HaiYuan Faultsand XiangShan-TianJingShan Faults and about 43"china crustal " GPSstations data added in this region。The more dense GPS velocity fieldwill be gotten. Then with Three-dimensions Deep Fault DislocationInversion, the more credible sliding rates of HaiYuan Faults andXiangShan-TianJingShan Faults will be given. The results show that thereis 6.6～10.0mm/a of left lateral slip rates in the HaiYuan Faults. Thereis 3.9～5.6mm/a left lateral slip rates in the GanTang-TongXin segmentof XiangShan- TianJingShan Faults ,there is 0.85～1.0mm/a of leftlateral strike rates and about 1.8mm/a of thrust rates in theShuangJingZi-TongXin segment.4. the contemporary sliping rates of the ZhangLangHe-MaxianShanFaults, which the slip rates are very low and the conventional geologicalmethods are difficult to be applied, are not assured. We can get thesliping rates by using the three-dimension deep fault dislocationinversion ,the results show that there is 1.4～3.0mm/a of thrust rateson MaXianShan North Faults and about 3.0mm/a of left lateral strike onthe middle of the faults;there is 0.6～1.2mm/a of thrust rates onZhuangLangHe Faults with unobvious left lateral strike, these resultsare in accordance with the geological results.5. Based on the GPS and geology data, numerical simulation of thespeed field has been done to the study area through the Finit ElementMethod. The simulation results provide that the difference among the theAltyn Tagh fault system,the east Kunlun faults,the changma-HaiyuanFaults is obvious. The speed field between or among these fault beltsis steedy both in azimuth and value.6. The results gotten by the Finite Element Method in 2-dimensionallylinear elasticity space accordance well with the velocity field of theTibet Plateau. But because the time is limited, there are still a fewproblems in the physical parameter choice of the model,the constraintof the displacement nodes ,etc. There are a little disparity betweenthe results gotten from simulation and the real observation.