## 3 Results
### Identification of the Geological Structures and Field Investigation  
Identification of lineaments of geological structure was conducted using shaded relief map derived from DTMH at eight different azimuth angles as shown in Figure 4. The mapped lineaments were summarized and edited to determine the geological structures. The three-dimensional shaded relief map was then derived with the mapped lineaments and viewed from different angles to identify the topographic subsidence and validation of the mapped geological structure lineaments. The two mapped lineaments on the main slope face could be clearly identified and validated on three-dimensional shaded relief  
Figure 8: The SPOT5 image after 2005 event was overlaid on DTM5 three-dimensionally, viewing from west direction toward east direction, and lineaments of landslide scarp mapped were shown as the colored dash lines. Figure 9: The SPOT5 image after 2005 event was overlaid on three-dimensional slope map of DTM5 viewing from west direction toward east direction, and lineaments of landslide scarp mapped were shown as the colored dash lines. map when viewing from the east direction toward the west direction as marked by the red lines in Figure 10. The two lineaments were approximately 50 m apart, and intersected with the I-Lan Special Route 1 at about 11.4 km on the north side, and at about 13.9 km on the south side. The shaded relief map of the opposite slope behind the ridge was derived and displayed three-dimensionally with the mapped lineaments on opposite slope in Figure 4. The lineaments of geological structures were identified and validated as shown by the orange lines in Figure 11 viewing from west direction toward the east direction. To investigate the extension and attitude of the geological structures in the slope body, the two sets of lineaments on both sides of the ridge were approximated as straight lines and projected on the two-dimensional slope map in Figure 12. It appeared that the set of geological structure lineaments extended from the slope of the main study area through the slope body till reaching the opposite slope. By connecting the two sets of lineaments mapped on opposite slope surfaces of the ridge, the two geological structure surfaces through the slope body were formed. The status of the two geological structure surfaces were measured taking the shortest distance between the corresponding lineaments on opposite slope surfaces, and the statue of the upper surface was N13 \({}^{\circ}\)E dipping 23 \({}^{\circ}\)E, while the statue of the lower surface was N20 \({}^{\circ}\)E dipping 20 \({}^{\circ}\)E, respectively. There was likely a shear zone bounded by the two geological structure surfaces. Such identification would not be possible without DTMH which provided detailed topographic variations. Field investigations were conducted where the mapped geological structures appeared to intersect with the I-Lan Special Route 1 for further validation. Three out-crops were located in the field, with out-crops A and B located near the south intersection of lineaments and road close to the landslide slope, and out-crop C located near the north intersection of lineaments and road. The out-crops A and B were found near 13.9 km of the road as shown in Figures 10 and 12. The out-crop A was found to be a fractured dark gray rock with well-developed discontinuities with a spacing of about 25 cm and inner width of 1 mm as shown in Figure 13a. Figure 10: The three-dimensional shaded relief map derived from DTMH viewing from east direction toward west direction. Two lineaments were identified and marked by the red lines, the yellow dots marked the out-crop field investigation points A, B, C, and D.  
Figure 11: The three-dimensional shaded relief map derived from DTMH of the opposite slope over the ridge viewing from west direction toward east direction. Two lineaments were identified and marked by the orange lines on the opposite slope. The red lines indicated the lineaments on the main slope surface of the study area.