Seismic Deformationes Analysis Of Strong Earthquakes In Western Area By InSAR

China is located in a world-prone earthquake-prone zone.The West Sichuan-Tibet region is located between the Indian plate and the Eurasian plate.The two plates are constantly colliding and squeezing.As a result,many large earthquakes have occurred in the western region of China and its neighboring countries,which can cause huge impact on the economic,natural and social environments.Therefore,strengthening the monitoring of deformation in the western region and carrying out corresponding geodynamic studies are of great significance for studying the crustal movement of the plateau and the occurrence mechanism of earthquakes.However,in western China,the population is sparsely populated,the geological structure is complex,and the coverage and number of GPS stations are significantly less than those in the eastern region,resulting in less research on relevant focal mechanisms and deformation mechanisms.This paper makes full use of the advantages of In SAR data sources,such as a wide range of sources and large coverage,to study three large-scale earthquakes in recent years in western China and its surrounding areas,and to test the application effects of InSAR technology in different tectonic background earthquakes.On April 25,2015,a strong Mw 7.9 earthquake occurred in Nepal.The earthquake in Xigaze,Tibet,was strongly felt.On May 12 of the same year,another Mw 7.3earthquake occurred in the Kodari region located in the northeast of the main earthquake.On August 8,2017 and August 9,2017,Mw 6.5 and Mw 6.3 earthquakes occurred in Jiuzhaigou County of Sichuan Province and Jinghe County of Bortala County,Xinjiang Province,respectively.All four earthquakes are located in remote high altitude areas and lack sufficient ground deformation observation data.In addition,post-earthquake deformation due to stress changes in the lithosphere after the Nepal earthquake is comparable to that of the same earthquake.Therefore,the use of InSAR technology for coseismic deformation monitoring,and the use of SBAS-InSAR technology to analyze post-earthquake deformation in Nepal,are highly practical,and are of great significance for the study of seismogenic structures and crustal movements in remote areas of the plateau.This paper uses the Sentinel-1A/B image data provided by the European Space Agency?ESA?and the Japan Satellite Space Administration?JAXA?ALOS-2 satellite image data,using the two-rail differential interferometry process.The coseismic deformation fields of the Jiuzhaigou,Jinghe and Nepal earthquakes were obtained,and the sliding distributions of the Jiuzhaigou and Jinghe earthquakes were inverted by elastic dislocation models.At the same time,a direct solution model method was used to obtain the 3D coseismic deformation field of the Nepal Mw 7.9 earthquake.Finally,SBAS-InSAR technology was used to obtain the time series of LOS surface deformation in the Nepal region from May 2015 to June 2016.The study of this paper is as follows:?1?Seismic deformation analysis and fault slip distribution inversion of Jiuzhaigou earthquake based on Sentine-lA dataFrom the result of coseismic deformation,the Jiuzhaigou earthquake co-seismic deformation field is located at the convergence area of the Minjiang fault,Tazhang fault and Huya fault,and the deformed area shows the butterfly-shaped four-quadrant distribution characteristics.The maximum deformation of the radar line of sight is 12cm,and the maximum settlement is 21cm.The inversion results of the Jiuzhaigou earthquake indicate that the length and width of the faults are approximately 68 km and 40 km,respectively.The maximum slip of the fault is about0.87 m,the average slip is about 0.21 m,and the seismic moment is about 7.82×10¹⁸N·m.The moment magnitude is Mw 6.5,and the earthquake rupture is mainly concentrated within the depth of 5-15km underground.The faults are dominated by strike-slip and the surface rupture is very small.?2?Seismic deformation analysis of Jinghe earthquake based on Sentine-lA/B data and inversion of fault slip distributionFrom the result of coseismic deformation,it can be known that Jinghe earthquake deformed area is elliptical,and the long axis goes near the east-west direction.The results of LOS deformation upslope and upslope data are all uplifted and the maximum uplift is about 8cm.Jinghe earthquake inversion results show that the coseismic slip distribution is mainly concentrated along the strike 8-21 km and along the trend down In the 1-13km area,the maximum slippage of the fault is about 0.92m,the average slip is about 0.46m,the seismic moment is about 7.17×10¹88 N·m,and the corresponding moment magnitude is Mw 6.35.This earthquake uses the thrust motion as the Lord.The seismogenic fault of the Jinghe earthquake is the Kusongmu Weikan pre-fault,and this earthquake was the result of a shift in the deep part of the thrust fault zone in the northern Tianshan region of Xinjiang.?3?Comprehensive Analysis of InSAR Deformation in Nepal EarthquakeAccording to the results of the Nepal earthquake coseismic deformation,the Nepal Mw 7.9 earthquake deformed area is double elliptical,and the deformation center on the south side of the epicenter is characterized by uplift.The maximum uplift volume is about 1.2m.The deformation center on the north side of the epicenter is a settling feature.The settlement is about 0.7m.The coseismic results show that both the north-south deformation center and the south-north deformation center are located on the upper plate of the seismogenic fault,which has typical low-angle thrust-type seismic characteristics.Comparing the coseismic deformation field and the Mw7.3aftershock coseismic deformation field of the Mw 7.9 earthquake in Nepal,it was found that there is a northward-facing bulge near the center of the main shock coseismic deformation field,and wedges the deformation center on the north side of the epicenter.Nearby,and the protruding east area is the epicenter of the aftershock.The results show that there may be a triggering relationship between the main shock and the aftershocks in Nepal.In order to understand the three-dimensional motion of Nepal's seismogenic faults,we used the Sentinel-1A orbit-raising and orbit-reducing data to obtain a three-dimensional coseismic deformation field of Nepal Mw7.9earthquake using a direct solution model.The three-dimensional deformation field has both uplift characteristics and subsidence characteristics.The Nepal Mw7.9earthquake seismogenic fault has thrust characteristics.This paper uses 12Sentinel-1A satellite images and uses the SBAS-In SAR technology to obtain the post-earthquake LOS deformation field from the period of May 2015 to June 2016 in the earthquake area in Nepal.The results show that the area is within the earthquake area.LOS shows the characteristics of subsidence on the north side of the post-earthquake deformation field,and has obvious uplift characteristics on the south side.This paper studies the application of InSAR technology in the deformation analysis of different types of radar data sources and different types of earthquakes,and obtains the coseismic deformation fields of the Jiuzhaigou,Jinghe and Nepal earthquakes,and decomposes the line of sight of the Nepal earthquake into coseismic distortion into three-dimensional.Deformation field,to understand the three-dimensional motion of a seismogenic fault,using SBAS-In SAR technology to obtain the post-earthquake deformation field of Nepal earthquake,which has certain reference significance for the post-earthquake risk assessment.Studies have shown that In SAR technology has great advantages in monitoring the seismic deformation of high altitudes in the west,rare GPS stations,and difficult-to-observe areas in the field,and has achieved good results.This paper has important scientific significance for the occurrence mechanism of earthquakes and the geodynamics of plateau crust.