Research In Three-dimensional Crustal Deformation In Northeastern Margin Of Qinghai-Tibet Plateau

The formation of Qinghai-Tibet Plateau is the result of the Indian plate subduction andextrusion north-east to Eurasian plate, Continuous force makes the Qinghai-Tibet blockconstantly expanding to mainland. In the force of north-east to Indian plate, the northeasternmargin of Qinghai-Tibet Plateau block becomes the latest and an important component ofQinghai-Tibet Plateau, and this region as the Qinghai-Tibet Plateau of the marginal materialeastward shift, formed with a number of major faults. Northeastern margin of Qinghai-Tibetblock having a unique geological structure, with complex natural environment, belong toearthquake-prone area.In this paper, modern geodetic techniques such as GPS data and high precision levelingdata are used for researching and analyzing detailedly the three-dimensional crustaldeformation of the northeastern margin of Qinghai-Tibet block. Focus on researching Qilianmountain fault zone, Haiyuan fault zone, Liupan mountain fault zone and the north edge ofwest Qinling fault zone which are located in the northeastern margin of Qinghai-Tibet block.Fitting the level rate observed by GPS and the vertical rate by leveling respectively in thenortheastern margin of Qinghai-Tibet block. In order to analyze detailedly each fault’scompression and strike-slip characteristics, making the rate chart of parallel to the fault andperpendicular to the fault respectively. Qilian mountain fault zone is primarily to levorotatoryand thrust, the strike-slip rate is about4mm/a, the crustal shortening rate is about6mm/a;Haiyuan fault zone’s sinistral and strike-slip rate is4mm/a, the crustal shortening rate is5mm/a; Liupan mountain fault zone’s crustal shortening rate is6mm/a, the strike-slip rate isnot obvious; the activities of the northern west Qinling fault zone is priority to levorotatoryand level twist, vertical activities for this fault showed that the western is strong and theeastern is weak,it is opposite to vertical activities, level activities showed that the eastern isstrong and the western is weak. Finally, using the least squares configuration model work outof this area’s stain rate field, the conclusion is that this region’s strain rate is unevendistribution and the largest principal strain region is Haiyuan fault and Qilian fault. In thispaper, the northeastern margin of Qinghai-Tibet block vertical crustal deformation also madea detailed analysis, this area’s vertical movement showed mainly the inheritance movementwhich the mountain rise and the basin decline. Relative to the Baoji, the maximum rate ofrisen in Liupan mountain region, the largest rte reach to2.5mm/a, Maximum rate of decline inthe Weihe basin, Longxi basin, Linxia basin area, the largest rte reach to-2mm/a. This paper based on the theory of dislocation model, using the particle swarm optimization algorithm toinverse the three-dimension slip velocity of the Qilian mountain fault, the results show thatQilian mountain fault zone is primarily to levorotatory and thrust with the trend of theextrusion movement. Finally, this paper make a preliminary analysis of the dynamicmechanism on the northeastern margin of Qinghai-Tibet block deep.