Three-Dimensional Coseimic Defoamation Extration And Fault Slip Inversion Based On Multi-platform InSAR

Earthquakes are one of the most destructive natural disasters causing the result of landslides,mudslides,tsunamis and other disasters,and China is an earthquake-prone country.The Wenchuan Mw7.9 earthquake,Yushu Mw6.9 earthquake and Ya'an Mw7.0 earthquake cause serious losses of life and property.Thus,the extraction of high-accuracy coseismic deformation field based on the geodesy technology and inversion of fault slip based on the geophysical model are quite significant for the exploration of focal mechanism and comprehension of fault activity.Furthermore,it can promote the research of earthquake prediction.Differential Interferometric Synthetic Aperture Radar?DInSAR?becomes an indispensable technology in measuring coseismic deformation field because of wide coverage,high accuracy,full-weather and full-time observation,etc.This paper selected four ascending and descending image pairs of ALOS-2 and Sentinel-1A before and after the 2017 Iraq earthquake?Mw7.3?.On this basis,the LOS?Line of Sight?coseismic deformation fields were derived by the conventional DIn SAR method.The results show that the deformation field cover an area of about 60×70 km² with two clear deformation lobes?here refers to lobe A and B?which divided by an NNW trending bound.For ascending deformation fields,the maximum value of uplift in lobe A and subsidence in lobe B are approximately 100 cm and-30 cm;For descending deformation fields,the maximum value of uplift in lobe A and subsidence in lobe B are approximately 50 cm and-50 cm.All these characteristics reflect parts of the coseismic deformation mechanism.But for an earthquake event,the only one-dimensional?1D?co-seismic deformation provided by DInSAR issues in anamorphic displacements and biased source parameters.To overcome the limitations of DIn SAR,this paper studied Azimuth Pixel Offset?AZO?and Multiple Aperture InSAR?MAI?techniques to derive the coseismic along-track?AT?deformation.Meanwhile,this paper analyzed the theoretical and practical accuracy,sensitivity of two techniques.The results show that MAI is better at measuring the AT deformation than AZO techniques.To understand the mechanism of coseismic deformation accurately,this paper studied combining DIn SAR and MAI to reconstruct the three-dimensional?3D?coseismic deformation field by solving the linear equations.The results show that the deformation field cover an area of about 60×70 km² with two clear deformation lobes which divided by an NNW trending bound,too.In the UD?Up-Down?component,the maximum uplift appears in the lobe A is approximately 100 cm,while the maximum subsidence appears in the lobe B is approximately-50 cm;in the EW?East-West?component,the maximum westward displacements in lobe A and B are both approximately 50 cm;in the NS?Nouth-South?component,the motion is weak,but it also encompassed the maximum northward displacement in lobe A with value of 100 cm approximately.To evaluate the result,this paper simulated the 3D deformation fields by the fault parameters?published by United States Geological Survey,USGS?based on Okada dislocation model,then took profiles to make comparisons.The smoothness and tendency of profiles in EW direction are in agreement mostly,and the profiles in UD direction are in agreement quite well,the profiles in NS direction are in disagreement relatively.The residuals in EW,NS,UD directions concentrated in[-5,5]cm,[-10,10]cm,[-5,5]cm.The residuals are in centimeter level.Therefore,our results are reliable.According to the characteristics of three-dimensional coseismic deformation fields,the main fault is a thrust fault with NNW trending and small dip.After analyzing the vertical and horizontal deformation fields,this paper found that the city Sarpol-e-Zahab locate at the stress gathering region,thus it suffered the worst destruction.To obtain more accurate fault source parameters,this paper performed a two-step inversion to derive the fault geometric parameters and slip distribution based on the 3D and LOS coseismic deformation data sets,respectively.After comparisons,the results of two experiments are quite consistent with the existing researches.Based on the analysis of the residuals and slip distribution,the results based on the 3D coseismic deformation data sets are better.To evaluate the results of inversion based on two data sets,this paper simulated the LOS coseismic deformation fields based on Okada dislocation model.After calculating the residuals and analyzing the profiles'goodness of fit and residuals'histograms,this paper find that the standard deviation?Std?of residuals based on the 3D coseismic deformation data sets are 2.4 and 2.9 cm,respectively;and the standard deviation?Std?of residuals based on the LOS coseismic deformation data sets are 3.5 and 4.2 cm,respectively.Regarding the Std as the accuracy evaluation standard,the results of calculations reveal that the inversion of fault slip based on 3D coseismic deformation data sets improves the accuracy nearly 30%.It proves that the 3D coseismic deformation data sets have advantage in fault inversion.After considering the geologic structure background,the locations of main and aftershocks,the analysis of LOS and three-dimensional fileds,this paper finds that the Zagros mountain front fault is responsible to the earthquake.The fault length is 60 km,the fault width is 30 km,the strike is 352.63°,the dip is14.76°,the rake is 137.1°,the slip occurrence extends from 12 km to 18 km beneath the ground surface,and a peak slip of 6.53 m appears at the depth of about 14.5 km at southwest of the epicenter.Set??shear modulus?as 3.0×10¹⁰ Pa,the estimated seismic moment is 8.44×10¹⁹ Nm?Mw7.3?.It is an earthquake event with thrust movement and right-lateral strike-slip.This paper demonstrates the superiority of using the 3D co-seismic deformation fields on fault slip inversion.The studies can support the calculation of coulomb stress variation and analysis of fault interaction.Furthermore,the studies also help to understand the characteristics of regional fault activities and supply objective and reliable scientific information for the risk assessment of aftershocks.