## 3 Results and Discussions
### Case Study: Metro Manila, Philippines  
This research will focus on Metro Manila, also known as the National Capital Region (NCR). The region consists of sixteen cities and one municipality and serves as a commercial, educational, and cultural center for the Philippines. Metro Manila is the most densely populated region in the country, with a population density of approximately 20,000 people per square kilometer as of 2021, with an estimated population of approximately 13 million people. Due to migration from other parts of the country in search of better economic opportunities, the population has increased rapidly. In recent years, new residential and commercial developments have been constructed to meet the rising demand for housing and office space because of the population increase. For construction projects, a geotechnical investigation is necessary to determine the site's suitability for proposed developments. Due to its high population density, rapid urbanization, and earthquake susceptibility, Metro Manila is an excellent location for a case study to determine the significant liquefaction susceptibility. As shown in Figure 8, a total of 1656 geotechnical investigation data were collected from within and surrounding Metro Manila. Using GIS, the areas of each zone were then determined, and any areas larger than 1 km\({}^{2}\) were reduced through microzonation. This resulted in an increase from the original 1690 zones to a total of 2036 zones, shown in Figure 9. In addition, the centroids of each zone have been determined using GIS and are provided in latitude and longitude format. Figure 8: Locations of collected geotechnical investigation data. Metro Manila's susceptibility to liquefaction was evaluated in this study using the methodology developed by [PERSON] et al. [1]. This methodology employs the equation for the factor of safety (FS) against liquefaction, which is written in terms of the cyclic resistance ratio for earthquakes (CRR) and the cyclic stress ratio (CSR) resulting from the earthquake's shaking. The CSR is the seismic demand placed on a soil layer and is computed using the peak horizontal acceleration (PGA) at the surface of the ground caused by the earthquake. As discussed in the previous section, the DSHA was employed to estimate PGA. DSHA involves calculating the distance from the source of the fault and the magnitude of the anticipated earthquake. Within the context of Metro Manila, it was discovered that the Marikina West Valley fault has a prominent presence. The cities of Quezon City, Marikina, Pasig, San Juan, Mandaluyong, Pateros, Makati, Taguig, Paranaque, and Muntinlup are at risk if the fault line ruptures, as they all lie within 0-2 km of the fault line, shown in Figure 10. The NCR cities located farthest from the Marikina West Valley Fault are Malabon and Navotas. In this study, a parametric analysis was performed to determine the evolution of peak ground acceleration (PGA) in Metro Manila for earthquakes with magnitudes ranging from 5.0 to 9.0. The Marikina West Valley Fault is a major contributor to seismic activity in Metro Manila and poses a significant threat of a magnitude 6 to 7.5 earthquake. This earthquake could cause a significant number of fatalities and injuries. In the National Capital Region, Table 5 displays the range of peak ground acceleration at different earthquake magnitudes. Figure 9: Microzonation of Metro Manila, Philippines. Figure 10: Distance of Metro Manila Zones from Marikina West Valley Fault. \begin{table}
\begin{tabular}{c c c} \hline \multirow{2}{*}{**Magnitude**} & \multicolumn{2}{c}{**Range of Peak Ground Acceleration (PGA) Magnitude**} \\ \cline{2-3}  & **Minimum in g** & **Maximum in g** \\ \hline
5.0 & 0.12 & 0.15 \\ \hline
6.0 & 0.22 & 0.24 \\ \hline
7.0 & 0.32 & 0.34 \\ \hline
7.5 & 0.37 & 0.39 \\ \hline \end{tabular}
\end{table} 
Table 5: Range of PGA at different earthquake magnitudes in Metro Manila.