# 2-D Cross-Plot Model Analysis Using Integrated Geophysical Methods for Landslides Assessment
## 2 Methods
### Field Procedure  
In this study, 2-D resistivity and seismic refraction are designed in line. Six 2-D resistivity survey lines (HR1-HR6) were designed with a length of 200 m (m) for HR1 and HR4 and 300 m for HR2, HR3-HR6. HR1-HR3 was oriented parallel to the slope failure, while HR4-HR6 was in a perpendicular direction to the slope (Figure 1d). The _Aktiebolaget Elektrisk Malmletting-Signal Averaging System_ (ABEM SAS 4000) was utilized to acquire the data with an electrode spacing of 5 m. The pole-dipole array was used for data protocol acquisition in providing comprehensive data resolutions. In seismic refraction, three survey lines (HS1-HS3) were designed with a length of 230 m and 115 m for HS1 and HS2-HS3, respectively, with geophone spacing of 5 m. HS1 and HS2 were designed parallel to the slope, while HS3 was oriented perpendicular to the slope. ABEM Terraloc Mark 8 (Mk8) was used as a seismograph to record the seismic waves. Table 1 shows the detailed of the survey lines. In this survey, four boreholes (BH) were provided, with two boreholes located inside the landslide area and another two outside of the landslide boundary (Figure 1d). The minimum electrodes spacing of 2-D resistivity and the length of the survey were chosen based on the research objectives and accessibility of the area. There are several factors considered in deciding the length of the survey, included the site constraint and depth of investigation. The pole-dipole array was chosen based on the deepest subsurface penetration, as well as the ability to provide a good resolution. Otherwise, the accessibility and site constraints were counted by selecting the best array to use (Figure 2). In addition, several factors that needed to be taken into account included the sensitivity of array to \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Methods**} & \multirow{2}{*}{**No Lines**} & **Total Length** & **Electrodes/Geophone** & \multirow{2}{*}{**Protocol**} \\  & & **(m)** & **Spacing (m)** & \\ \hline \multirow{2}{*}{**2-D Resistivity**} & HR1, HR4 & 300 & \multirow{2}{*}{5} & \multirow{2}{*}{Pole-dipole} \\ \cline{2-2} \cline{5-5}  & HR2-HR6 & 200 & & \\ \hline \multirow{2}{*}{**Seismic**} & HS1 & 230 & \multirow{2}{*}{5} & \multirow{2}{*}{-} \\
**Refraction** & HS2-HS3 & 115 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Survey lines of Ulu Yam. Figure 1: Ulu Yam study area: (**a**) landslide prone area in Malaysia-not to scale (modified from [34]); (**b**) geological setting of Peninsular Malaysia (modified from [56; 57]); (**c**) geology map (modified from [58]); (**d**) study area (the survey lines of two-dimensional (2-D) resistivity and seismic refraction was shown with red and yellow line respectively); (**e**) schematic diagram of the rotational-landslide of Ulu Yam. vertical and horizontal changes in subsurface resistivity, depth of investigation, horizontal data coverage, and the signal strength [59]. The pole-dipole array shows good horizontal coverage with significantly higher signal strength. The sensitivity section shows higher for large n factor as this array is more sensitive to vertical structure with good horizontal coverage [59]. Res2 Dinv software was used to process and interpret the data by using a mathematical algorithm to generate a 2-D resistivity inversion model. The inversion routine used by the program is based on the smoothness-constrained least-square method [60; 61; 62; 63]. The seismic refraction method was employed in this survey with a 5 kg sledgehammer and was used as a source of impulsive waves with 28 Hz geophones as a detector. A remote trigger geophone was used to trigger the seismograph at instant impact as the sledgehammer smacked on a steel striker plate. Several stacking is needed to increase the signal-to-noise ratio by repeatedly smacking the striker plate to produce the energy. In this survey, seven shot points were carried out, as five shot points were inline, while the others were the positive and negative offsets.