# Ground Displacement in East Azerbaijan Province, Iran, Revealed by L-band and C-band InSAR Analyses
## 4 Results
### InSAR Displacements and Field Observations
In Tabriz plain, the situation is the same, but the exact volume of extracted water is unknown due to many illegal deep-water pumping wells. Figure 6: Scatter plots and correlation coefficients of (**a**) time span 1 (2015–2016) against time span 2 (2016–2017), (**b**) time span 1 (2015–2016) against time span 3 (2017–2018), and (**c**) time span one (2015–2016) against time span four (2019–2020). In Tabriz plain, we obtained groundwater information of 10 piezometric wells as gathered by the regional water organization (RWO). Regular monthly measurements of the water level in Tabriz basin are available since 2001. We only plotted groundwater time series from 2015 to 2019. The water fluctuation and ground subsidence (SBAS results) at the same level along with the linear regression are shown in Figure 10. The level and behavior of piezometric wells are different. Wells S1, S2, and S2 have a very low water level ranging from 0 to 4 m, probably because they are not deep enough to conduct accurate measurements, while some wells, such as S7 and S10, have a higher water level ranging from 20 to 55 m. In some wells, such as S3, S7, and S10, seasonal fluctuation is evident, while in wells such as S5, the water level was stable or gently rose from 2015 to 2020. One reason for the gentle water rise in the subsiding area could be related to the synthetic recharge of wells by sewage water of large infrastructure such as the Tabriz petrochemical factory or power plant. Figure 7: Mean vertical velocity map of study area from (**a**) PALSAR-2 L-band and (**b**) Sentinel-1 C-band during 2015–2020, (**c**) displacement profile from A to B, and (**d**) displacement profile from C to D. Black stars show locations where field observations were carried out (see Figure 9). Blue pushpins in (**a**) show locations of wells where regular groundwater measurements are available. Purple circles in (**b**) are displacement, atmospheric, or topographic phases that are not observed in (**a**). Thick green and yellow lines indicate railway and first-degree networks, respectively. A comparison between water level and InSAR displacement in Figure 10 shows that ground subsidence matches with water level decline in some of locations, such as S8 and S9. Unfortunately, water measurements at S9 were not completed and there are some gaps without regular measurement. In other locations far from the subsiding area, such as S4 and S10, ground water fluctuation and InSAR displacement are in good agreement, which implies that the ground water level and InSAR displacement have a direct relationship. Nevertheless, in locations such as S3, ground displacement  
Figure 8: Scatter plot of PALSAR–ALOS-2 versus Sentinel-1 velocities. Figure 9: Subsidence evidence at different locations in Shabestar basin. Locations of images are shown in Figures 1c and 7a. does not follow ground water fluctuations. In Tehran basin, the same issue happened in some piezometric wells [54]. At the heart of the subsiding area in Tabriz basin where S9 is located, the mean displacement value is \(-195\) mm, which is the highest subsidence value among the listed wells. In contrast, the corresponding mean coherence value of S9 is about 0.56, which is lower than other known pumping stations. Figure 11 shows that an increased mean coherence value can result in a slower displacement rate. When the mean coherence value is high, it could be an indicator of slower changes in agricultural activities and vegetation growth of the study area. Comparing the spatial distance of the wells reveals that closer wells have similar mean coherence values, which implies that soil moisture and geomorphological characteristics of the wells may be related to mean coherence values over the time span. In Figure 11, S1 and S2, at the upper margins of the subsidence area, are spatially close to each other, and not surprisingly, their mean coherence values are 0.69 and 0.71, respectively.