Study On Surface Deformation In Sichuan And Yunnan Using InSAR

Sichuan and Yunnan are areas where earthquakes occur frequently in my country,and there are many faults caused by tectonic movements.The more conventional methods used in fault activity monitoring are mainly divided into leveling and global positioning systems.These conventional monitoring methods are effective for limited discrete points,but if the surface deformation is monitored,conventional methods cannot be achieved.Synthetic Aperture Radar Interferometry(InSAR)makes up for this deficiency.It can monitor planar surface deformation,has the advantages of high spatial resolution,high time resolution and is not affected by time and climate,and provides favorable conditions for interseismal deformation,coseismic deformation and deformation activities that cannot be monitored by conventional methods.Radar coherence is one of the most important indicators of InSAR application.The quality of coherence directly determines whether InSAR technology can be used.This paper first studies the functional model between the normalized vegetation index(NDVI)and coherence.The linear model and power function model are used to invert the relationship between radar coherence and normalized vegetation index,which provides reference data for the selection of radar images and the layout of GPS points;in the study of fault activity,the elastic half-space homogeneous position Based on the wrong theoretical model,taking the Qinghai Mangya Earthquake,Changning Earthquake and Rongxian Earthquake as examples,the coseismic deformation field,inversion source parameters and inversion calculation of coseismic slips were studied.Finally,InSAR was used to study parts of Sichuan and Yunnan Inter-seismic deformation of the fault.The research contents and contributions of this article are as follows:(1)In order to study the quantitative relationship between radar coherence and NDVI,this article takes the Guangdong Pearl River Delta region as an example,and establishes linear regression and power function regression models based on 2017 coherence and NDVI data.Through the f test,comparing the accuracy of the two models,we found that the accuracy of the linear regression model is better than the power function model in spring and winter,but lower than the power function in summer;we used the linear model and the power function model to predict the 2016 beads.The coherence of the triangle area is found to be higher than the linear function.Therefore,the power function model is used as the empirical model of NDVI and coherence.Finally,the model is used to predict the coherence of Yunnan area and obtain relatively high accuracy.(2)Synthetic aperture radar differential interferometry(D-InSAR)was used to obtain the coseismic deformation fields of the Mangya earthquake,Changning earthquake and Rongxian earthquake in Qinghai.Taking the Mangya earthquake and Changning earthquake as examples,the Okada elastic half-space uniform medium position was used Fault model inversion of seismic fault geometric parameters and fine slip distribution.The results show that the surface deformation field caused by the Mangya earthquake is an elliptical deformation zone with a maximum displacement of 34 mm along the line of sight of the radar wave.This earthquake was mainly the result of the action of the thrust fault.The thrust fault has a trend of 142.8degrees and a dip angle of 63.2 degrees.,The focal depth is 1.89km,the sliding is mainly concentrated in the range of 4-9km along the strike and 1-5km along the trend,the maximum sliding amount is 133mm,the moment magnitude is Mw5.141;the Changning earthquake caused a 130mm deformation in the line of sight,this The earthquake is mainly the result of thrust fault action.The fault strikes 121°,the dip angle is 40°,the focal depth is 2.2km,the slip is mainly concentrated in the range of 2-7km along the strike and 2-7km along the trend,and the maximum slip is 470mm.M0 is 5.308*10¹⁷ Nm.The moment magnitude is Mw5.787;the co-seismic deformation of Rongxian earthquake occurred about 7 km northeast of Rongxian,about 9 km east-west,and about 13 km south-north.The ground deformation is±14mm in the line of sight(LOS)direction.A new deformation pattern was found in the interferogram before the earthquake,with a diameter of about 5.8 km,located 25 km northeast of Rongxian and 5 km northwest of Weiyuan.The maximum deformation is about 23 mm,which is much larger than the co-seismic deformation of the Rongxian earthquake.The source of the Rongxian earthquake is located near the shale gas production well.The focal depths of these three earthquakes are much shallower than those of natural earthquakes on the Qinghai-Tibet Plateau,so it can be judged as an earthquake induced by artificial activities.(3)In order to study the fault activity in Sichuan-Yunnan region,this paper uses Sentinel-1A C-band data from October 2014 to July 2019,and adopts time series InSAR method to successfully obtain the deformation rate map of Sichuan-Yunnan region.The results show that the deformation rate near the Xianshuihe fault zone in Sichuan and Yunnan is between-5mm/a-5mm/a.The maximum settlement rate is located at the intersection of Ganning fault,Kangding fault and Yalahe fault,and the maximum uplift rate is near Xinlong county.Obvious deformation gradients appear on both sides of the fault,and the maximum deformation difference on both sides of the fault can reach 10mm/a.The fault deformation mainly comes from the post-earthquake deformation and the crustal compression on both sides of the fault.By comparing the deformation rate of two adjacent frames and the rate obtained with GPS,it is found that the results of this paper have certain reliability.