# Ground Displacement in East Azerbaijan Province, Iran, Revealed by L-band and C-band InSAR Analyses
## 4 Results
### InSAR Displacements and Field Observations  
Figure 7a,b shows the mean vertical velocity of SBAS results extracted from LOS rates and Equation (5) for PALSAR-2 L-band ascending images and conventional velocity map of C-band (Sentinel-1) descending images, respectively. There are two main displacement features in results of both L-band and C-band datasets with an NE-SW trend in Shabestar and Tabriz basins. Although velocity precision and height estimations during SBAS analysis show that some uncertainties may still remain in the results (Appendix A, Figure A1), the associated motions in the two datasets suggest a dominant long-term downward movement peaking at up to \(-\)100 and \(-\)120 mm/year, respectively. Figure 7c, d shows the ground subsidence rate along profiles A-B and C-D (shown in Figure 7a,b) from east to west. The A-B section for Sentinel-1 and PALSAR-2 shows good agreement, but at some locations, there are differences up to 4 cm. The subsidence rate in the first 12 km of profile A-B is higher in the Sentinel-1 results. On the contrary, the subsidence rate in the rest of the profile is higher in the PALSAR-2 results. In profile C-D, the results of PALSAR-2 and Sentinel-1 also show a similar pattern. Since the time spans of PALSAR-2 and Sentinel-1 datasets are very close, the reason for the cm-scale difference between their results in section A-B might be related, first, to the temporal decorrelation of the Sentinel-1 dataset and the high level of uncertainty in conventional InSAR analysis. Second, the wavelength of PALSAR-2 images is longer than that of Sentinel-1 images, and the sensitivity of the two datasets is different in detecting ground displacements. The correlation between PALSAR-2 and Sentinel-1 results along the profiles A-B and C-D, are 0.81 and 0.85, respectively. We also compared the SBAS InSAR map of PALSAR-2 data and the InSAR map of Sentinel-1 data for the whole study area. Figure 7 shows a cross comparison of the results. The correlation of the two maps is 0.6, and the mean vertical rate of ground subsidence and standard deviation for PALSAR-2 results are \(-\)10 and  
Figure 5: (**a**) Statistical results of coherence changes for SAR pairs with nearly one year time span, and (**b**) mean coherence values of four time spans. 9 mm/year, respectively (Figure 8). For Sentinel-1, the mean vertical rate and standard deviation are \(-13\) and \(12\) mm/year, respectively. Geodetic measurements such as Global Positioning System (GPS) and precise leveling in the study area are lacking, and we only gathered time series measurements of piezometric wells in the Tabriz plain. In addition, we gathered field evidence in the Shabestar plain. As shown in Figure 9, many buildings in the Shabestar basin and adjacent areas have been damaged as a result of progressive ground subsidence. Site 2 in Figure 9 (see its location in Figures 1c and 7a), an old piezometric well that was established approximately four decades ago, subsided at least 80 cm. Although the subsidence evidence around the old piezometric well is clear, it is unknown when the subsidence rate was accelerated. Some infrastructure in Shabestar city and two small towns, Shendabad and Vayqan (see their location in Figure 1), are also at immediate risk of ground subsidence. We drew a buffer of 5 km around the railways and major roads, and their proximity to the subsidence rates is presented in Table 2. The Shabestar basin is an unconfined aquifer with approximately 800 wells, 6 springs, and 161 qanats (traditional water extraction system in Iran), from which the extracted water in 2014 was estimated to be around \(88\times 10^{6}\) m\({}^{3}\)[13]. The number of deep wells not only in the study area but also in other large basins of Iran, such as Tehran basin, has increased. The latest public report shows that the number of legal/illegal wells in Tehran increased more than eight times over 44 years (1968 to 2012) [54].