## 5 Discussion  
Several studies have been carried out to investigate the causes of surface deformations in the Bolvadin region, [5; 6; 8]. There is no debate about the primary cause of surface deformation which is thought to be hydrological changes. However, there are different approaches about the effects of the tectonics. While [5] do not accept the effect of tectonic movements on ground surface deformations, [6] suggest that even though there was no destructive earthquake, intensive micro-seismic activity, and related reasons may have affected the formation of surface deformations. Ground level measurements with GPS and leveling show the rate of deformation on specific points around faults and fissures. Although these kinds of techniques provide precise measurements, they are limited to discrete locations. In this study, the ground deformation analysis of the entire Bolvadin region is performed by using the multi-temporal InSAR technique with Sentinel-1 TOPSAR data. Initially, LOS deformation velocity maps are produced for ascending and descending tracks as shown in Figure 4. Later on, vertical and horizontal (E-W) displacements are generated by decomposition of ascending and descending LOS  
Figure 9: LOS displacement time series of point P1 vs. temporal evolution of groundwater level at well no 28372 are shown together for (**a**) Asc.-160. (**b**) Des.-65 tracks. Location of the well is shown in Figure 4c,d. velocities, Figure 5. It is quite clear that the southern and western parts of the city have been exposed to vertical deformation as a whole. Towards the south, the subsidence rate increases and reaches up to 35 mm/year, most probably due to increasing groundwater extraction in the agricultural fields and thickening of the alluvial deposits. Deformation rate highly correlates with the lithological units of the region as most of the vertical deformations is observed in soft alluvial sediments and approaches to zero as we move away from alluvial sediments. In order to evaluate the possible effects of the Bolvadin fault entering the city from the east, deformation rates are examined with profiles of vertical velocity field across the fault. Figure 5 shows four profiles that perpendicularly cross the fault strike and its probable southwest continuation beneath the alluvium. Vertical and horizontal (E-W) mean deformation velocities over profiles are shown in Figure 10. There is no obvious or consistent vertical or horizontal deformation velocity change across the Bolvadin fault that might be indicative of tectonics origins. However, especially AA' and BB' profiles passing through soft alluvium sediments show significant variation across the Bolvadin fault. These asymmetric deformation patterns must be mainly due to the different amount of materials types within alluvial sediments because aseismic slip on the Bolvadin fault is expected to produce subsidence not on the northern side, but on the southern side (i.e., hangingwall) of the fault. The deformation rates of the CC' and DD' profiles are more stable in short time periods as they are situated over more compacted lithological units. When the profiles are examined, vertical velocities in the far field away from the Bolvadin fault are in general roughly the same, that is, there is no differential motion (i.e., downtown of hangingwall southern block) across the fault that might have been caused by creep on a normal fault that dips to the south, implying that the fault has no apparent contribution to the observed subsidence. We compare water surface area of Eber Lake and LOS displacement time series for ascending and descending orbits. As shown in Figure 8b,c, a clear correlation between the seasonal variation of water surface area of Eber Lake and displacement time series is revealed when the long-term linear subsidence trend is removed from the LOS displacements. There is a lag time between the peak level of the lake water surface area and the displacement time series.