Study On Co-and Postseismic Deformation By InSAR Observations

Interferometric Synthetic Aperture Radar（InSAR）technology,as an all-day,all-weather and high spatial resolution earth observation technology,provides advantageous conditions for seismic deformation monitoring.Large earthquakes often bring great disaster to human life,fortunately,they happen very infrequently.Compared with the large earthquake,the frequency of strong earthquake is very high,and strong earthquake will cause greater casualties and property losses.Therefore,it is of great significance to research strong earthquakes for preventing and mitigating earthquake disasters.In this paper,two strong normal fault earthquakes are selected as the research objects,namely the 2020 Nima Mw 6.3 earthquake and the March 2021 Thessaly earthquake sequence in Greece.We process Sentinel-1 data based on InSAR technique to obtain the co-seismic deformation of the 2020 Nima Mw 6.3 earthquake and the March 2021 Thessaly three earthquakes（Mw>5.5）in Greece,process a series of interferograms spanning one year after the Nima earthquake based on Small Baseline Subset Interferometric SAR（SBAS-InSAR）technique.The seismogenic mechanism,co-seismic Coulomb stress triggering and regional seismic hazard of the events are researched.The main research work and conclusions carried out in the thesis are as follows:1.Based on Sentinel-1 ascending and descending tracks images,we obtained the line-of-sight（LOS）co-seismic deformation field of the 2020 Nima Mw 6.3 earthquake and used the PSOKINV package to invert the fault geometry and slip distribution constrained by the co-seismic deformation.The results show that 1)the co-seismic deformation field shows an elliptical,and a maximum LOS displacement of with no rupture to the surface;2)The epicenter location was（33.18°N,86.88°E）at a depth of 7.4 km,and the causative fault had a N29.1°E strike and 50.2°dip;3)Most co-seismic slip was concentrated at depths between 3 to 12 km with a peak value of 2.0 m at 7.4 km.2.24 Sentinel-1A ascending images acquired from 30 July 2020 to 13 July 2021 were used to obtain post-seismic deformation and investigate post-earthquake deformation mechanisms（such as afterslip and poroelastic rebound）.Regional seismic risk is also analyzed based on co-and post-seismic slip distribution.The results show that 1)the maximum cumulative post-seismic LOS surface displacement reached～6.5 cm and followed approximately a logarithmic function over time;2)The most afterslip was concentrated at depths between 0 to 12 km with a peak value of 0.2 m at 5 km;3)The post-seismic moment energy was about 5.04×10¹⁷ N·m in 308 days after the event,which was approximately 13.8%of the co-seismic moment energy;4)By analyzing the contribution of afterslip and poroelastic rebound to post-seismic deformation,it was concluded that afterslip is the main early post-seismic deformation mechanism;5)Future attention should be paid in the northern segment of West Yibug Caka fault and East Yibug Caka fault.3.Benefiting from the high temporal resolution of Sentinel-1,independent LOS co-seismic deformation fields were obtained for three earthquakes（Mw>5.5）in Thessaly,central Greece in March 2021.The results show that 1)the maximum LOS deformation was-36 cm for the March 3 Mw 6.3 earthquake,-12 cm for the March 4 Mw 6.0 earthquake,and-8 cm for the March 12 Mw 5.6 earthquake;2)The three earthquakes did not rupture to the surface,and the seismic faults are blind faults.Constrained by the independent co-seismic deformation field of the three Thessaly earthquakes,the fault geometric parameters and slip distribution of the three earthquakes were inverted using the PSOKINV package.The results show that 1)the seismogenic faults of the Mw 6.3 mainshock on March 3 are two NE-dipping（42.0°）normal faults,and the maximum slip of the primary fault is 1.05 m,at a depth of 6 km;2)the seismogenic fault of the Mw 6.0 earthquake on March 4 is a normal fault of the NE-dipping（44.5°）with a maximum slip of 0.9 m at a depth of 6.48 km;3)The seismogenic fault of the Mw 5.6 earthquake on March 12 is a south-dipping（35.5°）normal fault with a maximum slip of 0.35 m at a depth of 3.34 km;4)By analysing the Coulomb stress changes,we conclude that the Mw 6.3 earthquake had a significant triggering effect on the occurrence of the Mw 6.0 and Mw 5.6 earthquakes.