Retrieving Three-Dimensional Co-Seismic Deformation of the 2017 Mw7.3 Iraq Earthquake by Multi-Sensor SAR Images

Abstract

The Mw7.3 Iraq earthquake on 12 November 2017 was the largest recorded earthquake in the Zagros Mountains since 1900. In order to quantitatively analyze the co-seismic deformation caused by this earthquake, both the ascending and descending SAR images from the Japan Aerospace Exploration Agency’s ALOS-2 and the European Space Agency’s Sentinel-1A satellites were collected to implement the conventional differential interferometric synthetic aperture radar (DInSAR), multiple aperture InSAR (MAI), and azimuth pixel offset (AZO) methods. Subsequently, the three-dimensional (3D) deformation field was reconstructed over an area of about 60 × 70 km2 by a combined use of the line-of-sight (LOS) motion (detected by the DInSAR method) and the along-track (AT) motion (detected by the MAI method) through the weighted least square method. The experiment indicates that the ALOS-2 satellite performs better than the Sentinel-1A sensor in larger-magnitude earthquake deformation monitoring. Furthermore, the MAI method based on phase differencing has a better performance than the AZO method based on SAR amplitude correlation, as long as the coherence of the interferograms is sufficient. The maximum co-seismic displacements in the up–down, north–south, and east–west directions are approximately 100 cm, 100 cm, and −50 cm, respectively. After comparative analysis between the obtained 3D deformation field and the simulated deformation field with the fault parameters published by the USGS (United States Geological Survey), both co-seismic deformation fields are highly coincident, and the residuals between both (in different directions/dimensional) are in the magnitude of centimeters. Considering the geological structure in the earthquake region and factors of the LOS and 3D co-seismic deformation—such as the trend and location of the deformation bound, the different sign of displacements in hanging wall and footwall, and the locations of mainshock and aftershock—the preliminary conclusion is that the Zagros Mountain Front fault is responsible for the earthquake.