# Characterizing Micro-Displacements on Active Faults in the Gobi Desert with Time-Series InSAR
## 4 Results and Discussion
### The Structural Geology of the Jiujing Region
#### 4.2.3 The Subsidence of JJ5  
Block J5 subsided by 0.26 mm a\({}^{-1}\) (Figure 6), likely caused by movements on F\({}_{\rm c}\), F\({}_{\rm b}\), and F\({}_{\rm d}\). Along F\({}_{\rm b}\), JJ28 (southern side) and JJ5 (northern side) are displacing eastward by 0.09 mm a\({}^{-1}\) and 0 mm a\({}^{-1}\), respectively (Figure 7). JJ5 is clearly stable but based on the orthogonal decomposition of maximum velocity (Section 3.4), JJ28 is displacing towards the northeast (N35\({}^{\circ}\)E) at 0.16 mm a\({}^{-1}\), indicating crustal shortening along F\({}_{\rm b}\) in the northeast direction and that F\({}_{\rm b}\) is a reverse fault. The vertical deformation pattern in Figure 6 indicates JJ28 has an average uplift rate of 0.14 mm a\({}^{-1}\), whereas JJ5 has subsided by 0.26 mm a\({}^{-1}\). This indicates F\({}_{\rm b}\) is dipping towards the south and JJ28 is the hanging wall of the reverse fault.  
F\({}_{\rm c}\) appears to be another active fault causing the subsidence of JJ5. JJ5 is horizontally stable while, as shown in Figure 7, JJ9 (the west side of F\({}_{\rm c}\)) is displacing towards the west by 0.33 mm a\({}^{-1}\). This indicates crustal extension along F\({}_{\rm c}\) in an east-west direction. Meanwhile, Figure 6 also shows a vertical velocity contrast between the eastern and western sides of F\({}_{\rm c}\), where JJ9 is uplifting by 0.17 mm a\({}^{-1}\) on average, which is much higher than that at JJ5 (\(-\)0.26 mm a\({}^{-1}\)). This indicates that JJ9 and JJ5 represent the footwall and hanging wall of F\({}_{\rm c}\), respectively, and that F\({}_{\rm c}\) is a normal fault dipping towards the east.  
The difference in vertical displacement between JJ5 (subsidence rate 0.26 mm a\({}^{-1}\)) and JJ4 (uplifted by 0.09 mm a\({}^{-1}\)) is 0.35 mm a\({}^{-1}\), shown in Figure 6, which indicates that F\({}_{\rm d}\) is vertically active. However, F\({}_{\rm d}\) is horizontally inactive, whereas the E-W displacements along the two sides of the fault plane are similar, according to Figure 7. Since F\({}_{\rm d}\) is NW-SE-oriented and because the entire Jiujing granite pluton is influenced by a NE-SW directed maximum principal compression, F\({}_{\rm d}\) is more likely to be compressional than extensional.  
Figure 10: Vertical displacement along cross-section AA\({}^{\prime}\) shown in Figure 6. This cross-section is formed from 300 PS displacement values sampled along the cross-section line and shows the annual relative movements within each fault block. The marked faults are interpreted from the PS displacement maps and they are illustrative, showing the sense of fault movement and general direction of faults.  
According to the vertical deformation pattern in Figure 6, it can be estimated that F\({}_{\text{d}}\) is north dipping. In this way, JJ5 is actually part of the F\({}_{\text{d}}\) footwall.  
F\({}_{\text{20-1}}\) is a normal fault dipping towards the northwest [43] and JJ5 is a part of the F\({}_{\text{20-1}}\) hanging wall, in theory. The PSI data in Figure 6 suggests there is a slight vertical displacement rate difference between the two sides of F\({}_{\text{20-1}}\), where JJ5 (western side) is subsiding, on average, 0.26 mm a\({}^{-1}\) more than JJ6 (subsiding at 0.20 mm a\({}^{-1}\)). In conclusion, JJ5 is the normal fault's hanging wall of F\({}_{\text{c}}\) and F\({}_{\text{d}}\) and the reverse fault footwall of F\({}_{\text{b}}\). The combined effect of F\({}_{\text{c}}\), F\({}_{\text{b}}\), and F\({}_{\text{d}}\) contributes to the overall subsidence of JJ5. Their spatial relationships are clearly illustrated in Figures 6, 7 and 10.