High-precision Seismic Deformation Monitoring By Time-series InSAR And Study On Yutian Earthquake Sequences

Interferometry Synthetic Aperture Radar(InSAR)technology has become an important means of monitoring surface deformation with the characteristics of all-time and all-weather ground monitoring and high spatial resolution,and has been widely applied to the field of seismic deformation monitoring.But the two-track D-InSAR technology,which is the most commonly used in seismic coseismic deformation monitoring,is affected by spatiotemporal decorrelation.There is obvious decoherence in the water area and the densely vegetated areas.At the same time,it is also vulnerable to the influence of atmospheric delay error,which would contaminate deformation field and affect source paraments inversion.Therefore,high-precision seismic coseismic deformation research is of great significance for future seismic deformation monitoring and parameter inversion.On June 26,2020,a Mw 6.3 earthquake occurred in Yutian area,Xinjiang,northwest of Qinghai Tibet Plateau.The region also experienced the 2008 Ms 7.3 earthquake,the 2012 Mw 6.2 earthquake and the 2014 Mw 6.9 earthquake over the previous 12 years.These three earthquakes are called Yutian earthquake sequence together with the 2020 Yutian earthquake.Fault activity is active in the Yutian region,and several major earthquakes have occurred in a short period of time,seriously affecting the public,yet the high altitude and harsh environment of the area make it difficult for traditional measurement tools to work Therefore,the use of InSAR technology to investigate the connection between earthquake sequences in Yutian can enhance the understanding of the seismogenic mechanism,regional geological activity and the risk of surrounding seismic activity.At present,The Multi-temporal InSAR(MT-InSAR)can partly overcome the spatiotemporal decorrelation problem by selecting stable points,and improves the spatial resolution of deformation monitoring.It has been widely used in the study of inter-seismic and post-seismic deformation.In addition,the Sentinel-1 A/B satellite data can provide sufficient archived data before and after earthquakes.In view of this,based on the InSAR technology and the support of sufficient SAR archived data,the following research work is carried out for the acquisition of highprecision seismic isoseismic deformation and systematic study of the connection between seismic sequences in Yutian:(1)Proposed coseismic deformation monitoring method based on stable points and interferogram pair optimization(SP-IPO).The main purpose is to improve the accuracy of the deformation field by two steps:selecting a suitable interferogram pairs and selecting stable points.Taking the Mw 6.4 earthquake near Hualian County,Taiwan,China,on February6,2018 as an example,the data processing flow is introduced in detail and compared with the results of traditional D-InSAR method.Then the coseismic deformation fields of 14 earthquakes in different regions and magnitudes are obtained by the high-precision coseismic deformation monitoring method.The deformation results show that the coseismic deformation accuracy can be effectively improved by setting the selected point threshold to eliminate the noise in the deformation field,and the introduction of atmospheric error can be significantly reduced by selecting appropriate interferograms.(2)Based on Sentinel-1A/B ascending and descending images,the coseismic deformation field of 2020 Yutian Mw 6.3 earthquake was obtained by the high-precision coseismic deformation monitoring method,and the geometric parameters and slip distribution of faults were inversed.The model results show that the coseismic rupture is dominated by normalslip motion and accompanied by minor strike-slip component.The main rupture is concentrated at a depth of 4-10 km with a peak slip of ～1 m and the moment magnitude are Mw 6.22.The Coulomb stress change model between Yutian earthquake sequences is also established to calculate the coulomb stress.The stress result show that there are obvious stress transfer and triggering between Yutian earthquake sequences,and the occurrence of 2020 Yutian earthquake was promoted by previous earthquakes.In addition,after the 2020 Yutian earthquake,the southwest segment of Ashikule,Xor Kol and Kuliya fault experience increase in coulomb stress,indicating that the seismic risk on these fault segments may be potentially increased.(3)Based on the time-series InSAR technology,the long-time deformation monitoring in the study area of Yutian Mw 6.3 earthquake was carried out by using the Sentinel-1A / B satellite ascending and descending data,and the post-earthquake deformation field of Yutian earthquake was obtained.The spatial and temporal evolution characteristics of the observed deformations were analyzed.The results show that the deformation characteristics observed about one and a half years after the2020 Yutian earthquake are not consistent with the general post-earthquake deformation decay pattern,and thus it indicates that the post-earthquake deformation of the 2020 Yutian earthquake is not significant.