## 4 Results  
### Three-Dimensional Deformation Field of the Landslide  
The three-dimensional geomorphic features of the Xiaomojiu landslide are shown in Figure 5, and the image was obtained from Google Earth. The landslide has a tongue shape in plain view, where most of the material is loosely broken. Based on the topographical features, the landslide belongs to typical large-scale landslides with an area of approximately 0.86 km\({}^{2}\) and is about 1350 m long and 600 m wide. The main sliding direction is about 46\({}^{\circ}\). The slope angle averages 30\({}^{\circ}\) and reaches 40-50\({}^{\circ}\) in some places. According to remote sensing image interpretations, the rear edge and local areas on both sides of the landslide are severely damaged, and the surface vegetation is destroyed with the broken rock mass exposed. The middle part of the landslide presents transverse cracks formed by the tensile stress of the sliding mass (Figure 5). A caving zone with an area of about 100 m\({}^{2}\) can be seen in the middle of the front edge. In addition, a vertical expanding fracture zone was located at the left front of the slope, which was formed by the compressive stress due to the downward slope. Figure 6a-c shows the LOS displacement of the landslide obtained by the InSAR technique. Due to the NE direction aspect, ascending images of Sentinel-1 and PALSAR-2 were more favorable for deformation acquisition. The results of the two ascending images both showed that the cumulative LOS deformation of the landslide was about 20 cm during the two years, and the large deformation areas were mainly concentrated in the middle and front of the landslide. Figure 5: Diagram showing the three-dimensional morphology of the Xiaomojiu landslide from Google Earth (background: modified from © Google Earth 2021). In order to compare the differences in displacement obtained from different orbit data, we established three deformation profiles along with the horizon and slope directions (A-A', B-B', C-C' in Figure 7). The observation results from descending images are poor; therefore, the Sentinel-1 deformation results marked by yellow dotted lines showed minimal deformation. The displacement obtained from Sentinel-1 and PALSAR-2 ascending images is similar, and the deformation profiles (A-A', B-B') both showed about 10 cm of cumulative deformation. The deformation differences between the two ascending results are within the acceptable range caused by the difference in the satellite orbit angle and the identification ability of the SAR band. Figure 6: LOS accumulative deformation from the InSAR method; (**a–c**) are deformation results acquired from Sentinel-1 ascending, descending, and PALSAR-2 ascending data. Figure 7: Displacement comparison of three profiles. The red, blue, and yellow dotted lines represent three direction measurement results. (**a**) Deformation results of the landslide; (**b–d**) Profiles A-A’ B-B’ and C-C’. According to the method described in Section 3.2, the three-dimensional velocities were derived to better explain the landslide movement. Figure 8 shows the three-dimensional velocity field of the Xiaomojiu landslide with several areas of rapid deformation. Figure 8a shows that the Xiaomojiu landslide has large-scale vertical subsidence in the middle and front parts with a maximum deformation of 12 cm/a. Moreover, the significant stress failure in the rapid subsidence area will damage the rock mass, which corresponds to the tensile damaged area in Figure 5. Figure 8b,c shows the deformation velocity of the Xiaomojiu landslide in the east-west and north-south directions. The horizontal displacement velocity of the landslide in the middle and front areas was about 8-10 cm/a, whereas the displacement velocity of other areas was relatively minor, about 3-5 cm/a. Through the landslide's displacement velocity fields in the horizontal and vertical directions, we found that the rear part of the landslide was mainly subsidence.