## 4 Discussion  
The high-resolution DTMH derived from LiDAR point cloud data provided detailed topographic information, which enabled identification of the geological structure lineaments in this study. Such geological structure lineaments were further validated through field investigation of the out-crops. Mapping and identification of the geological structures would not have been possible without the high-resolution terrain information. The DTMs used in the previous research have resolutions of 5 m and 1 m [31; 32; 33], respectively, and no clear evidence of geological structures was found. The accuracy of the terrain model was limited especially in the vertical direction in the mountainous and steep ground areas. The vertical accuracy of 1-2 m or higher in the mountain area for DTM5 was reported. The identification of the geological structures relies on detailed information of the topographic variations, typically ground subsidence in the vertical direction, which might have been lost due to the accuracy limitation of DTM. A shear zone bounded by the identified geological structure surfaces was postulated in this study which appeared to be reasonable and was validated by comparing the projected shear zone to the borehole logging data of LTW04 and LTW05 in Figure 14. The logging data displayed the distribution of shear zone materials found in the cores, and the distribution was consistent with the projected shear zone bounded by the geological structures. Furthermore, the identified geological structures and shear zone provided supporting data for interpretation of the drill cores and field data, which provided information on distribution of the ground layers at the site. In order to understand whether the existence of the geological structures and shear zone would have affected the failure mechanism of the deep-seated landslide, a separate numerical model analysis was conducted. A slope model similar to the slope model in Figure 15 with the same ground layer, water table, and same material properties but without the shear zone was constructed for the numerical analysis. Figure 19 shows the resulting distribution of the maximum shear strain increment in the slope body. The potential sliding surface indicated by the maximum shear strain increment appeared to develop to a greater  
Figure 18: The mapped scarps of SPOT5 image and the crest and toe points of the potential sliding surface resulted from numerical analysis of profile X-X’ (WGS 84 coordinates). Points marked as state 2 indicated results of the slope model with shear zone (with geological structures), and points marked as state 1 indicated results of numerical analysis of slope model without geological structures. depth and formed a larger potential sliding surface. The resulting crest and toe points were also plotted in Figure 18 and marked as state 1. Comparing the sliding surface in Figure 19 to that of the model with the shear zone in Figure 16, it was found that the sliding surface of the model without the shear zone extended to a greater depth and up the slope reaching behind the ridge. The extent of the sliding depth was deeper than distribution of shear zone material in boreholes LTW04 and LTW05 and could not be verified by the borehole data. The crest point of the no shear zone model plotted in Figure 18 located at much further up slope just beyond the ridge, and was beyond the mapped scarp. In addition, no evidence in field and historical records were found to support subsidence at the crest area and related displacements caused by this potential sliding surface. Thus, the proposed slope model with the identified geological structures and shear zone appeared to be a more reasonable model, and provide satisfactory results supported by field evidence, historical records, and borehole data. The failure mechanism of the deep-seated landslide appeared to be significantly affected by the existence of geological structures and shear zone, which were unable to be located without the high-resolution LiDAR derived DTM in the previous study [15; 16; 17].