# 2-D Cross-Plot Model Analysis Using Integrated Geophysical Methods for Landslides Assessment
## 4 Discussion  
The result of 2-D resistivity and seismic profiles show the characteristic of the subsurface material for the study area. The failure zone was identified for this area as the existence of the fracture zone with the boulder, and may trigger the occurrence of the mass movement. The low resistivity region, indicated as a highly saturated zone, contributed to the factor of the occurrence mass movement as the soil profile dominated by the sand and sandy silt. The continuous infiltration of surface water and heavy rain as it is seeping through to the fracture area, and is accumulated, may trigger the instability of the slope, as the permeability, and the porosity of the soil is high. The disturbance of the soil properties with the variation of porosity and permeability increased the effective stress of the soil, which is able to trigger the mass movement for the instability slope. Previous research conducted by [PERSON] et al., in residual soil for the granitic area, shows the same characteristic in this area where the fracture and highly weathered mass contribute a major causative factor for slope failure [73]. These features lead to the movement of the seepage and underground water through it. The groundwater flow was determined as a plane of weakness for that research. In this case, the hillslope soil condition, with loose material dominant for all profiles, which able to trigger the slope failure under the continuous infiltration of the surface water above the water table. The occurrence of the fracture zones provided a wider zone for surface water to seep through to the soil and accumulate. The unstable condition, with loose materials and increased accumulation of water, triggered the occurrence of slope failure. The failure zone was identified for this area as the existence of the fracture zone with the boulder, and may trigger the occurrence of the mass movement. The presence of the boulder can be a key factor for the instability due to change and removing the rock that holds the slope in place [74,75]. Other than that, highly fractured zone and water-conducting zones are indicated by the presence of low resistivity zones, within the granite body. The thin layer of residual soil due to domination of the granite body at the slope face triggered the failure or landslide events. Figure 8 shows the water circulation pathway of the Gapis River associated with sediments in this survey area. Low resistivity values (HR6-HR2-HR1) are observed as the water circulation quite deep beneath this area associated with water from the Gapis River directed towards northeast to southwest (NE-SW). Other than, in HR3-HR4-HR5,  
the water circulation may be relatively shallow at this location at a depth of 5-20 m. The survey enables to characterize the unstable region along with the profiles as the existence of fracture and scattered boulders. The resistivity value of <1200 \(\Omega\)m at a depth of <20 m represents the weathered bedrock. Relatively, the unaltered bedrock generally has a high resistivity value of >7000 \(\Omega\)m and the elongate zone of lower resistivity mostly of the range of 500-1600 \(\Omega\)m parallel to topography interpreted as altered zones. The seismic refraction survey shows the bedrock was identified at velocity values of >3800 m/s. The first layer dominates with velocity values of <1200 m/s represented as highly weathered zones. The lower velocity values show that this zone had a high potential for instability to occur. The broad zones of low resistivity values (50-300 \(\Omega\)m) with the appearance of high resistivity values of (1200-2500 \(\Omega\)m) are associated with the fracture or failure zone along with profiles. Low resistivity region (<100 \(\Omega\)m), as the saturated zones, may correlate with high permeability of water-bearing fractures [76; 77]. In order to validate the geophysical results, a borehole record was used as supported data in providing realistic interpretations. In this study area, only two boreholes were in line with the geophysical survey: BH9 and BH10.