# Characterizing Micro-Displacements on Active Faults in the Gobi Desert with Time-Series InSAR
## 4 Results and Discussion
### The Factors Affecting Sentinel-1 Data
As wet sediments absorb the microwave radiation [50] and contribute a less backscattered signal to the sensor, the interferograms produced between dates with different moisture levels are less coherent than those with similar moisture content [51]. In addition to pore water presence, the accumulation of surface sediments not only decreases the surface coherence, but also impacts the vertical deformation data, with most typical cases around Ba'antan Basin in JJ11. As shown in Figure 15, the red PS points representing uplifting scatterer targets can be found in the middle and north parts of Ba'antan Basin, even though the entire Block JJ11 is subsiding due to the impact of F\({}_{20\cdot 2}\) and F\({}_{1\cdot 2}\). One interpretation is that this apparent uplift is due to the accumulation of  
Figure 15: The locations of Bantan Basin, Ba’antan Basin, and Jiujing Basin within vertical deformation (D\({}_{\text{U}}\)) patterns (black outlines indicate Quaternary sediments). surface sediment. This argument is supported by a past investigation that found that the Holocene sediments are still accumulating in the Jiujing region in modern times, with average accumulate rates of 0.1 and 0.4 mm a\({}^{-1}\) at Ba'antan Basin and Jiujing Basin, respectively [23], indicating that modern sediments alter the surface of the granite section. Alternatively, lower moisture levels may cause uplift by unloading, or reduced dielectric delay of the radar signal, but this still requires further investigations. Overall, the Quaternary sediments are present only in Bantan Basin, Ba'antan Basin, and Jiujing (Shiyuejing) Basin while most of the surface at Jiujing is characterised by exposed granite, as shown in Figure 3. The surface sediments only generate localised impacts and do not significantly influence the overall deformation pattern in the Jiujing region. The surface rock eroded by natural aeolian, and alluvial processes will lower the surface elevation and make the rock appear as if it is subsiding. Past studies of granite or grandolorite erosion rates under arid, semiarid, temperate, and alpine climates show rates on the order of 10\({}^{-3}\) mm a\({}^{-1}\)[52, 53, 54, 55, 56, 57], three orders of magnitude smaller than the average surface deformation rates measured here. Hence, granite erosion rates under natural processes are too low to have a significant effect on observed deformation rates. Thus, the lack of vegetation cover, minor and predictable groundwater changes, and low erosion rate of granite are considered to have no significant impact on the observed vertical and horizontal velocity patterns. The accumulation of modern sediments appears to trigger the uplift in some parts of the granite surface but the influence on vertical deformation patterns is limited to Bantan Basin, Ba'antan Basin, and Jiujing (Shiyuejing) Basin. Furthermore, the coincidence of the deformation patterns with observed discontinuities in optical data strongly indicates that the vertical and eastward displacement of the PS points presented in Tables S1-S3 are mainly the result of active tectonic fault movements. In general, the long time-series analysis reveals movements, which, although very small,  
Figure 16: The locations of Bantan Basin, Ba’antan Basin, and Jiujing Basin within horizontal deformation (D\({}_{\text{E}}\)) patterns (black outlines indicate Quaternary sediments). are in broadly consistent directions over contiguous areas. There is noise and small-scale local variation (which in turn lead to variable standard deviations) but the regional pattern within the blocks is broadly consistent. Therefore, the results are sufficiently convincing to be considered as real fault-controlled surface displacements.