## 1 Introduction  
The 2017 Mw7.3 Iran-Iraq Earthquake occurred in a region where the pattern of major plate convergence is well constrained (Figure 1). Although some studies and institutions (USGS (United States Geological Survey), GCMT (Global Centroid Moment Tensor), CENC (China Earthquake Networks Center)) published some source parameters [1; 2; 3; 4; 5; 6; 7], the variable slip on the main fault related with this earthquake is still uncertain. In order to accurately derive the variable slip on main fault, this present conducted detailed fault inversion using the 3 Doseismic deformation fields reconstructed by a combined use of the DInSAR and Multiple Aperture InSAR (MAI) measurements, based on both the ascending and descending SAR images obtained by L-band ALOS-2 and C-band Sentinel-1A sensors respectively. Nowadays, the geodetic data of GPS and DInSAR have been extensively used in earthquake fault inversion. Althoughoseismic GPS data is good at providing 3D surface displacements at individual observation locations, labor power, and material resources cost is great. Meanwhile, the spatial density of GPS sites is limited. In recent years, the DInSAR method is developing with continually launching of new SAR satellites. Because it has a few significant advantages [8], such as high resolution, shorter revisit interval, wider coverage, etc., that is widely applied in fault slip inversion at present. However, the DInSAR observation is only sensitive to displacements in the line-of-sight (LOS) direction of radar. Therefore, only one component of the surface displacement vector was brought in the fault slip inversion. As a result, uncertainties of fault source parameters arose from data resources and data incompleteness, and the accuracy of source parameters estimation is restricted. To overcome the limitation, the Multiple Aperture InSAR (MAI) measurements was widely used to provide valuable information about azimuthal surface displacements [8; 9; 10; 11; 12]. Considering the heading angle of the ascending- and descending-pass direction is varying, totally four different displacements vectors can be observed by combing the DInSAR and MAI measurements. As a result, the 3D deformation fields can be reconstructed [13; 14; 15; 16; 17; 18; 19; 20; 21] to provide accurate data for fault slip inversion and increase the inversion efficiency. The previous study [22] measured the AT (along-track) deformation of the earthquake by the Azimuth Pixel Offset (AZO) and MAI method, respectively. The comparison results of two methods show that the MAI method is better at observing the AT (Along Track) deformation. At the same time, the 3D deformation fields of the earthquake were reconstructed by combing the DInSAR and MAI  
Figure 1: Shaded relief map of study area and image coverage. The yellow star indicates the epicenter of the mainshock (Mw 7.3). The red dots show the aftershocks with magnitude higher than Mw4.0 before 17 November 2017. The blue solid squares indicate the five cities with intensity reaching up to VI or higher. The black and red rectangles mark the coverage of SAR images. The dark red line represents the boundary between the Iraq and Iran. method [22]. But the low frequency (e.g., L-band SAR) is more sensitive to ionosphere [23; 24; 25], so it was necessary to remove the relative azimuth shift caused by ionosphere to obtain better deformation fields. In this paper, the SAR data sets of ALOS-2 and Sentinel-1a are used firstly to derive the deformation fields around the epicenter. During the procedures, we used the Precise Orbit Ephemerides for all images acquired and applied the range split-spectrum method [26; 27] to estimate the differential ionospheric phase, and then mitigate the relative azimuth shift caused by ionosphere in the MAI interferogram. The accuracy of the 3D coseismic deformation fields was promoted. Then this paper focus on testing the effect of using the 3D coseismic deformation fields on fault slip inversion.