Research On Seismogenics And Fault Movement Of Iraq Halabjah Earthquake Based On InSAR Technology

InS AR technology has been widely used in subsidence monitoring,earthquake and volcanic research since it was proposed.InSAR technology in displacement has the advantages which are large area,good continuity and high accuracy compared with other technologies.The application of InSAR technology in seismic research can obtain the scope of earthquake influence and the degree of damage caused by earthquake by the acquired coseismic deformation field,what's more,the accurate and reliable source parameters can be obtained by using the coseismic deformation field as the constraint.Earthquakes is the most intuitive reflection of surface deformation caused by earthquakes,which is an important reference index for studying focal mechanism and seismic structure.After the focal parameters are obtained,the seismic problems can be solved and parameters information such as depth,length,location,inclination angle,sliding direction,fracture time and initial jump amplitude of fault displacement can be predicted,and reconstruct the motion model.Based on the SAR images of Sentinel-1 ESA,the co-seismic deformation field was obtained by D-InSAR technology and the time-series surface deformation was obtained by SBAS-InSAR technology for the super-strong earthquake occurred in the Halebuja area of northern-east Iraq at 21:18 on November 12,2017.Based on Okada model,the functional relationship between subsurface faults and coseismic deformation field produced by earthquakes is constructed.The source parameters and static Coulomb stress model are inverted by Levemberg-Marquardt(L-M)nonlinear least squares algorithm.This thesis studies the following questions:(1)Inference of seismogenic mechanism by surface deformation induced by earthquakes.The seismogenic mechanism is inferred from the surface deformation caused by the earthquake,and the coseismic deformation field of the Iraqi earthquake is obtained by D-InSAR technology.To ensure the accuracy of the results,the two orbit data of ascending and descending orbit are selected for analysis.The result that serious ground deformation caused by earthquakes and the earthquake caused a rise of about 50 cm,in the upper plate and a drop in the lower plate to 40cm.Although the results of orbit lift analysis show that the deformation value is different from that of the descending orbit,but the deformation trend is the same.So the seismogenic mechanism of earthquakes is thrusting fault.In addition,there is a slight uplift in the South-East direction of the earthquake,so the earthquake is accompanied by strike-slip component.The result shows that the earthquake is a thrusting strike-slip fault.(2)Inversion of seismic source parameters based on Okada model.To solve the focal mechanism of the Iraq earthquake,the focal parameters are inverted based on Okada model.Firstly,the coseismic deformation field acquired by D-InSAR is sampled by quadtree down-sampling,then,the functional relationship between appropriate fault parameters and coseismic deformation field is established based on Okada model,,and the focal mechanism solution is obtained by L-M nonlinear least squares algorithm.The results show that seismic rupture length is 44.5 km,width is 16.1 km,fault dip is 8 degrees,rupture zone depth is concentrated between 14~17 km,and earthquake release moment is 0.97×1020.The diagonal line in the southeast-northwest direction of the fault zone coincides with the fault in the earthquake.The upper wall moves up along the plane of the fault zone and the lower wall moves down accordingly.Studies shown that the earthquake is a thrusting strike-slip fault.At the same time,the earthquake has a little of strike-slip with the angle is 140.68° and the sliding is 3.83m.The conclusion is the same as that the moment tensor of earthquake.(3)Obtaining time series surface deformation before earthquakes in this area.For the catastrophic earthquake in Iraq,the time-series analysis of the fault where the earthquake occurred and the analysis of the surface activity before the earthquake occurred in this area can provide strong support for the follow-up study of the earthquake situation in this area.In order to obtain the time-series deformation of the region,using the SBAS-InSAR technology obtained the time-series surface deformation through the 18 SAR data published by ESA.The results show that in the two and a half years before the earthquake,the faults were relatively active in this area,and there were different degrees of deformation near the faults.The maximum uplift about 43 mm/yr and the maximum subsidence reached 51 mm/yr in the area.Using GPS data to analyze the whole fault plate,it was found that the plate moved northward on average by 2 cm per year,which indicated that the crust in this area was relatively active before the earthquake.