Research On The GPS Crust Deformation Field Of The Northeastern Margin Of The Tibetan Plateau Afler Wenchuan Eatrhquake

The GPS technology has played an important role in the recognition of deformationfield caused by earthquake nucleation, the observation of the coseismic displacement fieldand the monitoring of the postseismic crustal movement and change since it was appliedwisely to the monitoring of crustal deformation. It has become one of main methods foranalyzing crust deformation field which is about earthquake. On May12,2008, the WenchuanMs8.0earthquake occurred. This must have a great influence on crust deformation fieldaround because the magnitude is large. Hence, it is necessary to study the characteristics ofthe postseismic crust deformation field using the GPS data. This paper studied thepostseismic crust deformation field of northeastern margin of the Tibetan Plateau zonebased on GPS data in different period. The main work of the paper as followed:1. The implication of the characteristic of postseismic short-term deformation innortheastern margin of the Tibetan Plateau zone was discussed based on the period1999～2007and2007～2009year.Analyzing the Zhuanglanghe fault and the middle and eastern Qilian fault with profileacross these two faults, the results showed that the slip rate of these two faults changeobviously before and after the Wenchuan earthquake; The coseismic displacement fielddistribution of the Wenchuan earthquake was established by spherical dislocation model,and it showed that major change did not come from coseismic influence, but postseismicinfluence though coseismic displacement have an effect on their slip rate; The deformationcaused by viscoelastic relaxation in one year after the earthquake was computed, but theresult showed it was so small that can be neglected; The slip distribution of afterslip ofthe Longmenshan fault was obtained by inversion, then the deformation in northeasternmargin of the Tibetan Plateau zone caused by this slip distribution was computed, and theresult showed it be neglected; Analyzing variety of the Oula vector of the block motionbefore and after the earthquake, the result showed, under the influence of coseismicdisplacement distribution, the differentiae of block motion adjustment has an importantinfluence on the form of crust deformation after the earthquake; The analyzing showed thatthe form of the characteristic of postseismic short-term deformation in northeastern marginof the Tibetan Plateau zone was not caused by postseismic deformation mechanics, but the differentiae of blocks motion adjustment made block boundary motion obvious in themulti-block system like the northeastern margin of the Tibetan Plateau.2. The characteristic of postseismic crustal surface deformation field in northeasternmargin of the Tibetan Plateau zone was study based on the period1999～2007,2007～2009and2009～2011year.The strain rate field (maximum shear strain rate field and surface strain rate field) ofthe northeastern margin of the Tibetan Plateau zone was obtained by the least squarecollocation method, and the characteristic of strain rate field was analyzed, the resultsshowed that the variety of the strain rate field was obvious during the period2007～2009year, and it was recovered during the period2009～2011year; The slip rate was computedby block Oula vector model, and the characteristic of crustal deformation at different scalefrom fault by profile across fault, the results showed that strike slip rate of the Tuolaishanfault, the Lenglongling fault and Jinqianghe fault was increasing obviously, deformation offaults was obvious especially across faults within50km, the slip rate of faults and profileacross fault during the period2009～2011year was similar to themselves compared with theperiod1999～2007year.3. Locking and the distribution of the slip deficit of the main faults and the varietyafter earthquake.To study the strain accumulation of the the main faults in northeastern margin of theTibetan Plateau zone using the GPS observation and the variety after Wechuan Earthquake,the locking and the distribution of the slip deficit of the faults was inversed based onnegative dislocation model, and the characteristic of strain accumulation of deep fault wasanalyzed, this showed that the locking degree of the Jinqianghe, Maomaoshan and thesouthern segment of Liupan Shan fault was the highest before earthquake and became morehigher during the period2007～2009year, the locking degree of the Tuolaishan fault, theLenglongling fault became more higher during the period2009～2011year, the variety ofthe locking degree of the Jinqianghe fault was small and it remained higher, the lockingdegree of others became weak, this may because the crustal deformation be effected byJapan9.0earthquake. The potential large earthquake of he Jinqianghe fault will be relative higher in the further by overall analyzing the the characteristic of the crustal deformationfield.