# Characterizing Micro-Displacements on Active Faults in the Gobi Desert with Time-Series InSAR
## 4 Results and Discussion
### The Factors Affecting Sentinel-1 Data  
Atmospheric effects on the SAR data were corrected during PSI processing, so the observed vertical (D\({}_{\text{U}}\)) and eastward horizontal (D\({}_{\text{E}}\)) displacements may be caused by five factors: vegetation growth, groundwater level, surface sediment movement, surface rock erosion, and tectonic movement. Beishan lies within the semiarid environment of the Gobi Desert, with very little vegetative cover; therefore, the impact of vegetation is assumed to be negligible and thus excluded. The average annual evaporation is 3200 mm, but the annual precipitation is only 60-120 mm and is concentrated in the summer months from July to September. Groundwater is recharged by precipitation, and the peak recharging period is in April despite the maximum precipitation being in July and August. Most of the rainwater in the summer period is removed by the high evaporation in this region, so the groundwater recharging in these months is low [31,48]. Groundwater recharge is expected to swell the ground surface seasonally in relation to the variations of local precipitation and evaporation. The Valley View Fault, Nevada, southwest USA has a similarly arid climate to Beishan. A case study from [PERSON] [49] indicated groundwater can generate a maximum of 3 mm of seasonal amplitude due to the impact of hydraulic pressure. In the case of Beishan, the highest groundwater recharging is in April, which means the peak of the seasonal amplitudes is expected to occur shortly after this period due to the highest groundwater recharging amount. However, within the average time-series analyses shown in Figure 9a-f, this kind of seasonal amplitude is not considered significant. This indicates that the groundwater, which could exert the hydraulic pressure  
Figure 14: The schematic diagrams to illustrate: (**a**) the sinistral shearing of the Jiujing granite region due to the impacts of NE compression, where the long ellipse axis (AA\({}^{\prime}\)) marks the direction of elongation and the short axis (BB\({}^{\prime}\)) marks the direction of shortening and (**b**) the shearing properties of high-angle faults (also known as antithetic strike-slip faults, marked by axis DD\({}^{\prime}\)) and low-angle faults (also known as synthetic strike-slip faults, marked by axis CC\({}^{\prime}\)) under the NE compression. Axis XX\({}^{\prime}\) refers to wrench strike. Modified after Wilcox [1]. necessary to trigger seasonal uplift, is unlikely to have an impact in Beishan, confirming that groundwater has very little impact on surface deformation here. The Quaternary sediments that cover the surface of granite blocks may also affect the measured Sentinel-1 data by masking the tectonic movements or causing significant spatial and temporal decoherence. In the case of Jiujing, this is mainly due to the existence of pore water and the deposition of sediments. As shown in Figure 3, most of the surface sediments within the Jiujing region are distributed at Bantan Basin, Ba'antan Basin, and Jiujing (Shiyuejing) Basin. To combine the information in Figure 3 with the deformation patterns in Figures 6, 7, 15 and 16, depictions were produced to improve the understanding of the impacts of Quaternary sediments on surface deformations, where the distributed sediments are circled by black lines (Figures 15 and 16). The Sentinel-1 data at Bantan Basin, Ba'antan Basin, and Jiujing Basin show a loss of coherence (with the deformation data missing) due to the presence of pore water in the surface sediments, as shown in Figures 15 and 16. That is because the subsidence triggered by normal faults F\({}_{16}\), F\({}_{18}\), and F\({}_{20}\) lowers the topographic height of Bantan Basin, Ba'antan Basin, and Jiujing Basin, causing a discharge of shallow groundwater, surface water, and flood water towards the basin centres [31,32]. This increases the saturation of the sediments.