# 2-D Cross-Plot Model Analysis Using Integrated Geophysical Methods for Landslides Assessment
## 4 Discussion
### 2-D Cross-Plot Model of Resistivity-Velocity  
From the previous discussion, the resistivity of \(<\)1200 \(\Omega\)m and velocity of \(<\)1200 m/s was identified as the threshold value for the material to undergo the mass movement. Note that this survey was acquired after the landslide event, where line HR2 and HS2 and HR4 and HS3 was crossing the landslide boundary while HR1 and HS1 outside formed the landslide boundary. From the graph (Figure 11) the resistivity-velocity ranged for line HR1 and HS1 is much larger as compared to the other two lines as this line is located outside from the boundary line of a landslide, which represents the originality of subsurface condition before the occurrence of the landslide. This explains the high resistivity-velocity range of the line. Figure 11: Graph correlation of resistivity–velocity for the same X–Y location for line: **(a)** HR1 and HS1; **(b)** HR2 and HS2; **(c)** HR4 and HS3. The 2-D cross-plot model was an enhancement work for cross-plot analysis in integrating different geophysical parameters. The goal of this work is to visualize and provide comprehensive subsurface images as well as to integrated both parameters of resistivity and velocity to be more precisely. In this study, the method was applied, and the final model of the 2-D cross plot was presented in Figure 12. Based on the previous discussion, this work was divided into three different stages of processing until the final data. Four quadrants were divided, representing four different characteristics of the subsurface, which are Q1 (\(\leq\)1200 \(\Omega\)m, \(\leq\)1200 m/s), Q2, (\(\geq\)1200 \(\Omega\)m, \(\leq\)1200 m/s), Q3, (\(\geq\)1200 \(\Omega\)m, \(\geq\)1200 m/s), and Q4 (\(\leq\)1200 \(\Omega\)m, \(\geq\)1200 m/s). The sorting analysis is applying to extract the values according to its depth and position that inline each other. Quadrant 1 (Q1) compromise of low resistivity and velocity values of \(\leq\)1200 \(\Omega\)m and \(\leq\)1200 m/s respectively. From the preliminary results of 2-D resistivity and seismic refraction, this value plays as a threshold factor for the occurrence of landslides event. Figure 12: Cont. Figure 12a shows both 2-D resistivity and seismic refraction with a 2-D cross-plot model of line HR1 and HS1, as it was located outside the landslide boundary. From the 2-D cross plot model, the majority of the values dominate by quadrant four (Q4). The model shows the failure plane was identified at depth \(<\)5 m, dominated by the first quadrant (Q1), marked with a solid black line. In Q1, the region represents the highly weathered zone with lower resistivity and velocity values. This zone indicates the potential zone for mass movements or triggered zone for slope failure. The Q2 region at depth \(<\)5 m (solid rectangle box), shows low velocity and high resistivity values, which indicates the presence of moderate weathered material for this profile. The highest region represents by Q3 may indicate the presence of hard materials/boulder, which is aided as an additional factor for the occurrence of landslide, besides the movement of water flow due to saturated zones. The Q4 region dominates with a resistivity value of 1-1200 \(\Omega\)m and a velocity of \(>\)1200 m/s. In Figure 12b,c, it shows the 2-D resistivity, seismic refraction, and 2-D cross-plot model for HR2 and HS2 and HR4 and HS3, respectively. As previously mentioned, this line was crossing the landslide boundary, which is generally the top surface cover with landslide material. From 2-D resistivity results, the saturated and highly weathered zones were identified at a resistivity value of \(<\)100 \(\Omega\)m and 100-1200 \(\Omega\)m, respectively. The seismic refraction profile shows the same characteristics where a low velocity zone identifies with a velocity of \(<\)1200 m/s. This zone mostly probably covers with loose material, such as sand with depth \(<\)5 m, as shown in the 2-D cross-plot model.