The Analysis Of Postseismic Deformation In Longmenshan Fault From GPS And InSAR

China is a region with frequently earthquake in the global continent,by the collision and compression of the Indian plate and the Eurasian plate,leading to the Tibetan Plateau circumferential region of intense seismic activity anomalies,with the complex geological structure and very active tectonic activity,showing the complexity and diversity of surface deformation,which become an ideal area for the study of seismogenic environment,as well as mechanism and evolution of the Earth.Located in the northeastern margin of the Tibetan plateau,Longmen Shan fault is the boundary of western Sichuan plateau and Sichuan basin.Seismicity more frequently in recent years,have occurred the 2008 Wenchuan Mw 7.9 earthquake and 2013 Lushan Mw 6.6earthquake,causing heavy casualties and property losses,triggered landslides,barrier lake and other secondary disasters after the earthquake.More and more studies show that due to stress change caused by lithospheric after the big earthquake can bring in postseismic deformation the same magnitude as the coseismic,which cannot be ignored.With the 109 GPS continuous sites and regional sites observation data in Longmen Shan fault from China Seismological Bureau and its subordinate provincial bureau,taking the internationally high-precision date processing software Bernese to calculate the GPS data beginning from the Wenchuan earthquake and end of 2015,obtained the coordinates of the time sequence of each site.Using the time series analysis to get the relax time of postseismic which is about 34 days,and by the logarithmic decay function of the relaxation after the earthquake to get the GPS postseismic deformation during the year of 2010 to 2015,which shows the crustal movement trend in Longmen Shan area after the Wenchuan earthquake.In which,the near field on the hanging wall of the fault have a significant postseismic deformation about 2⁵cm and have a movement trend to southeast direction;located in a stable South China the deformation in footwall is small and less than 10mm;Northeast of the fault segment has a 1²cm deformation and counterclockwise rotation along the fault to north direction;Southeast section has a relatively small level deformation with no fixed direction of movement.According to the 5 adjacent path,together 32 scenes L-band raw data ALOS/PALSAR which provided by JAXA,using InSAR software to process with a two-pass differential interferometric technology and external DEM acquired by the latest version V4.1 from SRTM mission,generated the LOS postseismic deformation field about one year after the earthquake.Calibrating by some high precision GPS data,we get the LOS deformation improved which adjacent strip become more consistency and continuity.Getting LOS deformation vary in the range of-15¹5cm one year after the earthquake.Large deformation in Longmen Shan fault located in hanging wall,which is consistent with the results obtained by GPS time series analysis.With the hierarchical model of the Tibetan Plateau and the fault slip model from USGS which inversed based on Wenchuan coseismic,and on postseismic viscoelastic relaxation theoretical model,to studying postseismic deformation mechanism.Using PSGRN/PSCMP program to simulate the time-depended deformation after the earthquake,we obtained the postseismic deformation from simulation during 2010²015.Compared with the postseismic deformation from GPS time series analysis,we found them fitted each better when take the elastic layer thickness in 45km and the viscosity coefficient in 1.0×10¹⁹Pa·s.