## 2 Materials and Methods
### Phase One: Development of Seismic Microzonation Map
#### 2.1.2 Soil Data  
Conducting soil site investigations for offshore areas was very costly and required specialists. Furthermore, only related parties were involved and willing to undergo the process. Thus, limitations occurred in terms of data availability. Soil data in this study were extracted from a soil investigation report submitted to the related parties in the process of constructing the offshore platform. The report was based on the cone penetration test with pore pressure measurements (CPTU) conducted in the study area. The report consisted of data, such as coordinates, depth of the borehole, soil profile, number of soil layers, total unit weight, thickness of soil layers, and soil type. These data were required for GRa, including soil shear wave velocity. However, shear wave velocity is not available in the soil investigation reports. Thus, the determination of shear wave velocity through CPT-Vs correlation equations was required in solving this problem.  
In the current study, six developed CPT-Vs correlations, which correlated Vs with the measured tip resistance (qc) and sleeve friction resistance (fs), and the correlation of Vs with qc only for the quaternary geological age, were selected. These correlation equations were developed based on soil types, such as sand, clay, and all soils [30; 31; 32]. In offshore  
Figure 4: Flowchart of research methodology.  
areas, normally the combination of clay and sand can be seen. CPT-Vs correlation equations adapted in this study are presented in Table 1. Values for soil shear wave velocities for each site were calculated by averaging the Vs from all soils and Vs calculated according to soil type. The same concept was applied by [PERSON] (2015) [33] in determining Vs for Malaysian offshore.  
After the data collection and screening process, there were \(11\) sites available with a total of \(19\) boreholes data. These sites were then classified according to soil type as suggested in ISO 19901-2. In the current study, the soils were classified according to the Vs of the first \(30\) m that were calculated using Equation (1). From the \(11\) sites, \(4\) were sited under soil type D and \(7\) under soil type E. Thus, D1-D4 represent sites for soil type D and E1-E7 represent sites for soil type E. The letter D represents soil type D and E represents soil type E while the number represents the numbering for the site. A sample of the soil model used in the present study is presented in Table 2.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Soil Type** & **Model** & **Equation for Vs** & **r\({}^{2}\)** & **Paired Data** \\ \hline All Soil & \begin{tabular}{c} Hegazy and Mayne (1995) \\ Mayne (2007) \\ \end{tabular} & \((101\log(\text{q}_{\text{c}})-11.4)^{1.47}\) (\(100\ \text{f}_{\text{s}}/\text{q}_{\text{c}})^{0.3}\) & \(0.70\) & \(323\) \\ \hline Sand & \
\begin{tabular}{c} Sykora and Stokoe (1983) \\ Hegazy and Mayne (1995) \\ \end{tabular} & \(134.1+0.0052\ \text{q}_{\text{c}}\) & \(0.61\) & \(256\) \\ \hline Clay &
\begin{tabular}{c} Hegazy and Mayne (1995) \\ Mayne and Rix (1995) \\ \end{tabular} & \(12.02\ \text{q}_{\text{c}}\) & \(0.319\ \text{f}_{\text{s}}\) & \(0.57\) & \(92\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Correlation of CPT-Vs used in the present study.  
Figure 5: Seismic time histories.