## 4 Results
### Multi-Temporal InSAR Results
#### 4.1.1 Mean Velocity Maps  
The mean deformation velocity maps obtained in LOS by multi-temporal analysis of ascending and descending datasets within the time period of October 2014 and October 2018 are shown in Figure 4. All measurement values are relative to a common reference point that is considered to be stable over the entire time period. Warm colors (negative values) highlight displacement that occurred away from the sensor while cold colors (positive values) show movement towards the sensor. Although results are displayed in the range of \(\pm\) 25 mm/year for visualization purposes, larger displacement rates are present at some locations. The velocity maps of the entire study area in Figure 4a,b show that subsidence is taking place not only in the town of Bolvadin, but also in almost all parts of the Afyon-Aksehir Graben, including the surroundings of Cay, Cobanlar and Sultandag towns. The majority of the PS points is found to be around the urbanized area. There are almost no measurement points over agricultural areas located around the settlement since great variations in the farmlands are expected in such a long analysis period. However, it is quite clear that the entire graben is exposed to severe subsidence. Figure 4c,d provides mean velocity maps focused on the Bolvadin region. Ascending and descending velocity maps show quite a similar deformation pattern and rates at most of Bolvadin, which is a sign of pure vertical movement. However, there are some areas like the southern part of the city that LOS deformation is different for ascending and descending dataset. That might be an indication of horizontal movement. For that reason, further processing and decomposition of LOS displacement into vertical and horizontal components is required for easier interpretation of movement.  
Only the projection of the actual displacement in the LOS direction can be detected by the SAR sensors. Another limitation of deformation measurement is the low sensitivity of SAR sensors to displacement occurred in the N-S direction [45]. In order to obtain 3D movement component, at least 3 different measurements are required obtained by different acquisition geometry. However, the N-S component can be neglected due to the low sensitivity of SAR sensors along that direction. Finally, availability of images obtained at ascending and descending acquisition geometry is enough to calculate vertical and horizontal (E-W) displacement components. Using the same decomposition method outlined in [46] with neglecting the N-S component, vertical and E-W horizontal mean deformation velocity maps are obtained for the Bolvadin region (Figure 5). In almost every region of Bolvadin, varying rates of subsidence are observed. The maximum vertical subsidence is observed to be around 35 mm/year in the southern part of Bolvadin. North and north-east parts shows relatively smaller deformation rate compared to south and south-west of the city. Although horizontal E-W movement is negligible in most regions, relatively small movement is observed in a small area in the west and specific region in the south.  
Figure 4: Mean Sentinel LOS velocity maps on ascending track 160 (**a**) and descending track 65 (**b**) in central Afyon-Aksehir graben. Close up view of Bolvadin region on ascending (**c**) and descending (**d**) tracks. P1, P2 and P3 points are used in time series analysis shown in Figure 6.