Observation And Modelling Of Coseismic,postseismic And Interseismic Deformation Field Of Fault Zone Using Time-series InSAR Techniques

A series of active blocks bounded by large strike-slip/thrust faults are distributed inside the Tibetan Plateau.Among them,the Kunlun fault is an important fault on the northern boundary of the Bayanhar block.Its seismicity and seismic hazard have been of extensive interest.The time-series InSAR technology and the sufficient long-term geodetic data provide key constraints on the crustal deformation characteristics of the Kunlun fault,reveal the lithospheric rheological properties of both sides of the fault.The acquisition of a large area of crustal deformation fields in the central and northern part of the Tibetan Plateau is helpful for understanding the complex tectonic processes and provides key model constraints for the dynamic process of deformation.Using D-InSAR and time-series InSAR technology,we processe and analyze Envisat/ASAR data during 2003-2010 and Sentinel-1A/B SAR data from 2015 to2020,supplemented by GPS data to obtain the earthquake cycle deformation of the Kunlun fault and in other complex tectonic areas(taking Hualien area in eastern Taiwan as an example)at different time periods,to analyze the difficulties in obtaining large regional InSAR deformation field,to study the relationship between coseismic slip,afterslip and aftershock distribution of major seismic events,the rheological properties and lateral heterogeneity of the lower crust of the Tibetan Plateau and the Qaidam Basin,and fault locking distribution revealed by the crustal deformation in the Kunlun fault.The main contents and conclusions of this study are as follows:(1)Based on ENVISAT/ASAR data from 2003 to 2010,the decade-scale postseismic deformation of the Kokoxili earthquake is analyzed.Using the improved orbital error and atmospheric error correction methods,the deformation evolution differences along different segments are obtained.The results show that postsiesic deformation after the Kokoxili earthquake has significant spatial range,magnitude and cross-fault asymmetrical characteristics.In general,the area of the postseismic deformation is?300 km×500 km,and the magnitude and distribution area on the south side of the fault are larger than those on the northern side of the fault.The maximum cumulative displacement observed by InSAR data(2003-2010)is?45-60mm(?92.5°E).The near-field deformation shows exponential decay characteristics,while the mid-to far-field deformation of the fault is close to linear decay characteristics.(2)Based on GPS data from 2001 to 2002 and ENVISAR/ASAR data from2003 to 2010,we study the postseismic deformation mechanism after the Kokoxili earthquake.The refined coseismic interferogram of Kokoxili earthquake is used,and the coseismic slip distribution model of Kokoxili earthquake is reconstructed.The results show that stress-driven afterslip and viscoelastic relaxation are the main mechanismes of the postseismic deformation.The main mechanism accounting for the far-field postseismic deformation(>200 km)is the viscoelastic relaxation of the upper mantle of the Tibetan Plateau(depth>70 km)and the upper mantle of the Qaidam Basin(depth>60 km),and the order of the transient and steady-state viscosity of the upper mantle is 10¹⁹-10²⁰ Pa s using biviscous Burgers rheological body.The afterslip(depth>20 km)helps to account for the significant cross-fault displacement gradient of the GPS rate profile.Afterslip in the shear zone and lower crust(>20 km)is?1 m during the first 3 years after the earthquake.It is found that the influence of shear zone/lower crustal afterslip on the estimation of the transient viscosity is up to three times.The combined model considering afterslip and viscoelastic relaxation shows that the optimal transient and steady-state viscosity of the lower crust of the Tibetan Plateau are 5×10¹⁸ Pa s and 4×10¹⁹ Pa s,respectively(the transient viscosity coefficients without afterslip considered are 2×10¹⁸ Pa s).The steady-state and transient viscosity of the lower crust in the Qaidam Basin are 1×10¹⁹Pa s and 6×10¹⁹ Pa s(the transient viscosity is 4×10¹⁸ Pa s without considering the afterslip).(3)Based on Sentinel-1A/B SAR data from 2015 to 2020,InSAR interseismic and 3D deformation field over a large area(?2000 km×350 km)in the central and northern Tibetan Plateau are obtained.It reveals that the ruptured segments of the Manyi and Kokoxili earthquakes still experiences significant postseismic deformation.The ruptured segments have not recovered to the complete locking.The cross-fault profiles of other fault segments reveal the interseismic strain accumulation along the locked segments.Based on the large-scale InSAR velocity field and cross-fault velocity profiles,the distribution of fault locking depth and slip rates along the fault trace is determined.It suggests that the slip rates of the Kunlun fault have the characteristics of systematic decay towards the western end.Based on the large slip rate(?8 mm/yr)and significant locking depth(?20 km)in the middle to eastern segment of the Kunlun fault,the seismic hazard of these segments is high.(4)Taking the 2017 Jiuzhaigou earthquake and the 2018 Hualian earthquake as examples,the fault structures of the buried faults at the eastern end of the Kunlun fault,as well as the relationship between the co-seismic slip and afterslip distribution of complex multi-fault rupture events are investigated.The seismogenic fault of Jiuzhaigou earthquake is studied using geodetic data.The optimal inversion results show that the coseismic slip is concentrated in the upper part of the crust and the seismogenic fault is dominated by left-lateral strike-slip movement.The Jiuzhaigou earthquake increased the Coulomb stress loading of?0.1-0.4 MPa in the western part of the Tazang fault.The coseismic and postseismic deformation of the Hualien earthquake are studied,and the complex multi-fault rupture characteristics of the seismogenic fault are revealed.The joint inversion of InSAR,GPS and teleseism-wave data reveals complex rupture process of the Meilun and Lingding faults,the westward-dipping faults and the detachment faults.The timeseries of postseismic deformation is calculated.The kinematic afterslip model reveals that the afterslip mainly occurred on the Milun fault,the Linding fault and the western-dipping fault.The earthquake cycle deformation contains rich information about fault structure,lithospheric rheology and fault locking state.The large-spatial-area and long-time-span geodetic observations reveal the differences of seismic cycle deformation and characteristics along various segments of the Kunlun fault.The decay of the fault slip rate at the west end of the Kunlun fault may be regulated by the secondary faults,which affect the long-term slip rate and locking degree of the main fault zone and the seismic hazard.