Research On Surface Deformation Monitoring Method In Earthquake-Prone Area With Vegetation Coverage Based On InSAR Technology

Earthquake is a serious natural disaster caused by crustal deformation.Monitoring surface deformation is one of the important contents in the study of seismic activity.The technique of synthetic aperture radar interferometry(InSAR),which can provide all-weather and all-time imaging with high resolution,has been widely used in surface deformation monitoring,especially in single object,local area and exposed area,but in the earthquake-prone area,the vegetation coverage area,its applicability is less studied.The Yingjiang Area of Yunnan province is one of the regions with the most frequent Southwest China earthquakes.The vegetation cover is thick and the deformation monitoring research has not been deeply discussed.Based on the data of ALOS PALSAR,Sentinel-1A and GF-3,the experiment of surface deformation monitoring is carried out in the earthquake-prone region of Yingjiang Area,which is based on D-InSAR and time-series InSAR,to explore and summarize the applicability of monitoring methods of ground surface deformation in earthquake-prone areas covered by vegetation,its significance is remarkable.The main achievements of this paper are as follows:(1)Using ALOS PALSAR ascending orbit data and based on D-InSAR,the two large earthquake deformation monitoring of 2008/08/21 M_W6.0 earthquake and2008/03/21 M_W5.1 earthquake in the study area is experimentally studied.The results show that there are two deformation centers in the two earthquakes,namely,the northwest uplift disk(upper disk)and the southeast subsidence disk(lower disk).2008/08/21 M_W6.0 earthquake:the maximum uplift along the LOS direction is about 45 cm,the maximum subsidence is about 38 cm;2008/03/21 M_W5.1 earthquake:the maximum uplift along the LOS direction is about 36 cm,the maximum subsidence is about 41 cm.The results show that the 2008 Yingjiang Area earthquake has not only the known strike slip motion but also the reverse fault rupture mode.(2)In view of the multi-earthquake phenomena in the study area from 2014/10/29to 2020/12/08,the surface deformation monitoring in the multi-earthquake area was carried out by using the 78-view-up and down-orbit Sentinel-1A satellite data.The results show that,in the period of 2014/10/29 to 2020/12/08,the eastern deformation rate of the northern segment of the Sudian Fault is about-20 to-25 mm/y,the western deformation rate of the northern segment is about 17 to 22 mm/y,and the eastern deformation rate of the southern segment of the Sudian Fault is about-15 to-20 mm/y,the western deformation rate of the southern segment is about 15 to 20mm/y,and the right-lateral strike-slip motion is maintained.The northeast deformation rate of the northeast segment of the Taping River Fault is about 13 to 18 mm/y,the southwest deformation rate is about-15 to-20 mm/y,the northeast deformation rate of the south-west segment is about 15 to 20 mm/y,and the southwest deformation rate is about-17 to-22 mm/y,maintaining the trend of left-lateral strike-slip movement.The time-series InSAR has a good indication for the identification of hidden faults.There is a small NW-trending hidden fault near Kachang,Yingjiang.(3)In view of the 2020/01/31 M_W4.0 Yingjiang Area earthquake,a deformation monitoring experiment based on GF-3 data was carried out and compared with the results of the more mature Sentinel-1A experiment.The results show that the GF-3 data indicate that the maximum subsidence is 23cm and the maximum uplift is 18 cm in the LOS direction.Sentinel-1A data shows that the maximum subsidence is 16cm and the maximum uplift is 17cm in the LOS direction.Both of them can monitor the effective deformation,and the results of the whole deformation are basically consistent with the deformation region,and their average coherence coefficients are about 0.32 and 0.25 respectively.In the same condition,the accuracy of GF-3 interference experiment is slightly better than that of Sentinel-1A data.(4)ALOS PALSAR,GF-3 and Sentinel-1A data are used to carry out the D-InSAR deformation monitoring experiment.When the vegetation coverage is less than 0.4,D-InSAR can keep good coherence,especially when the vegetation coverage is less than 0.2,the interference effect is the best,and when the vegetation coverage is more than 0.6,it is the low coherence When the vegetation coverage is more than 0.8,it is completely incoherent.When the vegetation coverage is less than 0.4,the time-series InSAR using Sentinel-1A data can keep good coherence,especially when the vegetation coverage is less than 0.2,the interference effect is the best,and the whole InSAR has no obvious incoherence,but when the vegetation coverage is more than 0.4,the coherence coefficient of sequential InSAR is 0.1-0.15.(5)In view of the monitoring of the ground surface deformation in the earthquake-prone areas covered by vegetation,through the comprehensive monitoring and exploration of the ground surface deformation with multi-data sources,multi-methods and multi-objects,a set of effective methods are summed up:in the earthquake-prone areas where the vegetation coverage is less than 0.4 and there are multi-source deformation such as large earthquake deformation,small deformation of fault zone and so on,the combined analysis method of using conventional D-InSAR to monitor large deformation and TS-InSAR method to monitor slow small deformation can provide more comprehensive and effective information of ground surface deformation in earthquake-prone areas,it can also provide a direct basis for revealing the characteristics of earthquake damage,seismogenic faults,hidden faults and so on.