## 5 Discussion
### New Understanding of Landslide Development
Therefore, it is not surprising that a large number of landslides revealed by both field investigation (Figure 14b) and InSAR technique (Figure 14c) slide towards azimuths 270 deg-360 deg and 0 deg-135 deg that coincide well with the dip directions of the strata and wedges (Figure 14a). Furthermore, some landslides in the study area slide to 230 deg-270 deg (Figure 14b,c), which are beyond the dip direction ranges of the bedding planes and wedges. These landslides might not be controlled by the strata and wedges but by other mechanisms. For example, weathered materials slide along the soil-rock interface and/or the interfaces formed by complicated combinations of discontinuities. Even though the aspects of slopes in Figure 14b,c cover similar ranges, some difference still exist. To better highlight those differences, the rose diagram of the aspects of the newly identified landslides through the InSAR analysis is plotted in Figure 14d. The InSAR analysis not only enhanced the observation of landslides with similar aspects as those in the field survey (e.g., 70\({}^{\circ}\)-130\({}^{\circ}\) and 230\({}^{\circ}\)-300\({}^{\circ}\)) but also revealed new landslides with aspects that are less predominant in the field survey (e.g., 10\({}^{\circ}\)-30\({}^{\circ}\) and 180\({}^{\circ}\)-210\({}^{\circ}\)). These newly identified landslides might be attributed to more complicated combinations of strata bedding planes and wedges that are difficult to identify in the field investigation. These observations suggest that the InSAR technique is powerful for identifying landslides in all dip directions and could improve the understanding on the significance of key factors controlling landslides at the regional scale, i.e., the stratigraphic occurrence and development of key joints in this study. The difference between the two data sets is attributed to the ability of InSAR to detect landslides on a regional scale. With this advantage, InSAR data can be used to analyze landslides over a wider spatial dimension, which is required for the correlation analysis between landslides and regional geological conditions. As shown in the rose diagrams of the slope aspects, landslides are not highly prominent along the strata dip direction but in the direction range of 70\({}^{\circ}\)-130\({}^{\circ}\) (Figure 14b,c), especially the landslides newly identified by the InSAR technique as being in the direction range of 105\({}^{\circ}\)-130\({}^{\circ}\) (Figure 14d). These directions indicate that the development of landslides could be affected by wedges. From a geological viewpoint, landslides controlled by wedges are relatively difficult to identify through field investigation due to the complicated combination of strata and joints. Nevertheless, by applying the large-scale InSAR analysis, the relationship between landslides and wedges could be more easily clarified. In summary, the identification of potential landslides in alpine regions is a difficult task because of the high altitude and complicated terrain conditions. Objectively, if landslides do not exhibit clear deformation evidence or are located in inaccessible ridge-tops, they might not be identified in field investigation. Moreover, the frequency of field investigations is relatively low because of high costs and limitations of time and resources. Consequently, reactivated landslides (such as the TS2 landslide in Figure 6) are likely to be neglected, especially after intense rainfall events in summer. Such missed detection could lead to not only the underestimation of landslide risk in alpine areas but also an incomplete understanding of landslide development. For example, the relationships between altitude and landslide as well as the landslide controlled by complicated wedges in the study area cannot be fully clarified through field investigation. In contrast, SAR satellites feature wide spatial coverage and short revisit periods, enabling the detection of landslides in inaccessible areas and reactivated landslides.