## 3 Results  
### Identification of the Deep-Seated Landslide and the 2005 Event  
The Lantai study area has a long history of deep-seated landslide activities with the first recorded event before 1980. The aerial photograph acquired on 30 November 1980 is the first aerial image record of the landslide as shown in Figure 6. We can observe the bare land exposed due to the landslide before 1980 with dash line marking the edge of the exposed ground, and some vegetation developed after the landslide. A lineament suggesting head scarp can be observed in the up-slope direction of the dashed line just beneath the road. Recurring landslide activities were reported in 2001 by Typhoon Nari, 2005 by Typhoon Haitang, and 2015 by Typhoon Soudelor, and some other smaller events. The events in 2001 and 2015 damaged the road with not so significant scale. Typhoon Haitang hit the Lantai area on 17 July 2005, bringing more than 1000 mm accumulated rainfall, and caused a significant landslide damaging the road and retaining structure severely. The SPOT5 images acquired on 16 March 2005 before and 11 March 2006 after the typhoon event are shown in Figure 7. In the SPOT5 image before typhoon (Figure 7a), the exposed ground can be observed with another scarp developed further up slope. The SPOT5 image after typhoon (Figure 7b) showed a significant enlargement and further development of the exposed landslide scar compared to the image before typhoon. The lineament of the scarp further up slope beneath the road can be observed clearly in both images. Observing the topographic and ground variations especially the head scarp caused by the landslide event in the images, the locations of scarp and landslide could be mapped. The SPOT5 image after the event was overlaid on DTM5 three-dimensionally in Figure 8, which accentuated the topographic variations and lineament of the scarp caused by the landslide. Through inspection from different aspects three-dimensionally, mapping of the scarp and the deep-seated landslide was finalized as shown in Figure 8. The scarps of the landslide appeared to enlarge and develop retrogressively up slope. A new scarp further up slope of the road was observed and mapped. Further validation of the mapped scarp was conducted by overlaying the mapped scarp and SPOT5 image on the slope map derived from DTM5 in Figure 9. It was found that the location of mapped scarps situated  
Figure 5: Illustration of the model slope constructed using DTM5 before the 2005 event, and no lateral displacement for the lateral boundaries and fixed boundary at base were assigned.  
where significant topographic variation showing subsidence was, and appeared to consist with the geomorphological characteristics of the deep-seated landslide.  
Figure 6: The first aerial photo image record of the deep-seated landslide of the study area taken on 30 November 1980 (WGS 84 coordinates). The bare ground exposed due to landslide is marked with the red dash line, and some vegetation recover can be observed.  
Figure 7: The SPOT5 images acquired on (**a**) 16 th March 2005 before, and (**b**) 11 March 2006 after the 2005 Typhoon Haitang event. The orange dash line marked the scars and edges of exposed ground caused by landslide (WGS 84 coordinates). The landslide scar in (**b**) was enlarged and developed further up slope compared to scar in (**a**).