Time series analysis of the pre-seismic and post-seismic surface deformation of the 2017 Iran–Iraq earthquake derived from Sentinel-1 InSAR data

A strong earthquake of M w 7.3 hit the border region between Iran and Iraq on November 12, 2017. Several InSAR-based coseismic inversion studies suggested that the earthquake occurred on a northeast dipping Mountain Front Fault within the Precambrian Arabian basement. In this study, we use multiple ascending and descending pass C-band Sentinel-1 images to study the earthquake's pre- and post-seismic surface displacements. We performed SBAS time series from June 2017 to March 2018 to understand the spatiotemporal evolution of the displacement before and after the November event. The pre-seismic time series displacement values range as high as –89 mm in descending pass and –96 mm in ascending pass. The pre-seismic time series analysis reveals subsidence between 84 and 0 days before the earthquake, which might be due to excessive groundwater pumping. The post-seismic displacements showed logarithmic decay, indicating afterslip. Even though the earthquake occurred on a blind reverse fault, we highlight that the post-seismic afterslip is composed of horizontal and vertical deformation components, which can be inferred from the variation in the displacement values of the descending and ascending passes. We believe that the small magnitude earthquakes and the January 2018 Mandali earthquake sequence in the Zagros Mountain region affect the spatiotemporal evolution of the November event afterslip. Research Highlights The temporal evolution of the pre-seismic displacement indicates significant ground subsidence before the earthquake. The pre-seismic ground subsidence due to excessive groundwater withdrawal combined with the interseismic strain accumulation might result in a reverse faulting earthquake. The results highlight the importance of the multi-temporal InSAR technique in the field of earthquake precursory studies. Several small magnitude earthquakes and the Mandali earthquake sequence that occurred after the earthquake affected the temporal evolution of the post-seismic afterslip. The pre-seismic deformation is dominantly vertical, whereas the post-seismic deformation is a combination of horizontal and vertical motion.