| Earthquakes are natural disasters with strong destructive power that seriously affect normal life and the economic development of human society.Currently,studying surface deformation caused by earthquakes and further exploring the activity status and seismic mechanism of faults is a hot topic.InSAR technology provides all-time,all-weather,and high-precision observations,it provides theoretical basis and support for fault activity,seismic mechanism analysis and seismic risk assessment,which can effectively monitor surface deformation caused by earthquakes and has become one of the main research methods.This paper presents a study on seismic deformation monitoring using the Madoi earthquake in the Bayankala block of the Qinghai-Tibet Plateau as an example.The D-InSAR,POT,and SBAS-InSAR techniques were used to investigate and analyze the Madoi earthquake’s co-seismic and post-seismic deformation.The main research findings and conclusions are summarized as follows:(1)The D-InSAR technique was used to extract co-seismic deformation fields in both ascending and descending radar line-of-sight(LOS)directions using Sentinel-1 A/B satellite image data.It was found that the northern block of the fault showed obvious uplift in the ascending deformation field,while the southern block showed obvious subsidence.The ascending and descending deformation fields had opposite characteristics,and the deformation profiles in the ascending and descending orbits had opposite trends.The surface rupture caused by the earthquake was obvious and irregular,and there were different deformation characteristics on both sides of the fault.The co-seismic deformation field in both ascending and descending orbits had obvious symmetry in sign,suggesting that the earthquake was a left-lateral strike-slip motion.The maximum LOS displacement caused by the earthquake was about 1.2 meters,and the maximum relative displacement across the fault in the LOS direction was about 2.2 meters.The POT technique was used to obtain the azimuthal and range deformation fields of the Madoi earthquake,and a three-dimensional deformation field solution was obtained by combining the co-seismic deformation information.The results showed that the east-west deformation component contributed the most to the co-seismic deformation,and the stress changes may have occurred at this location based on the bending of the fault.In the east-west deformation field,the northern block showed negative values and westward deformation,while the southern block showed positive values and eastward deformation,verifying the left-lateral strike-slip motion characteristics of the earthquake.(2)The co-seismic fault slip distribution was jointly inverted using InSAR and GNSS co-seismic deformation data as constraints,using the conjugate gradient method(SDM).The analysis showed that there were two slip centers in the joint slip distribution inversion,mainly concentrated at the eastern segment of the fault and the western side of the fault.The length of the fault that caused the earthquake was about 170 km,and it ruptured to the surface.The maximum slip was about 3.76 m,mainly concentrated within a depth range of 12 km.The static Coulomb stress caused by the co-seismic deformation and the spatial distribution of aftershocks around the earthquake were combined to show that most aftershocks occurred near the fault and a few occurred in the area where the Coulomb stress increases on the east and west sides.There was a certain amount of stress accumulation on the east side of the fault,which may have a higher seismic hazard.(3)Using SBAS-InSAR technology,we obtained time-series deformation characteristics and radar line-of-sight(LOS)average deformation rate of the madoi earthquake study area within one year after the earthquake.The analysis showed that the LOS average velocity near the northern fault zone ranged from-40 to-20 mm/yr,whereas that near the southern fault zone ranged from 20 to 55 mm/yr.The accumulated deformation near the northern and southern fault zones was between 15-50 mm and 20-55 mm,respectively,with maximum deformation values of-39 mm and 54 mm,respectively,near the fault.The fitted curve of the characteristic points indicated that afterslip mainly dominated the post-seismic deformation.By solely considering the effect of afterslip,we used the SDM to invert the fault slip distribution of post-seismic accumulated deformation.The results showed that the spatial pattern of fault slip distribution complemented the distribution of aftershocks,implying that afterslip mainly dominated the post-seismic deformation. |
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