# Shear-Wave Velocity Model from Site Amplification Using Microtremors on Jeju Island
## 4 Results
### SSP Site  
Figure 16 displays the observed and synthetic HVSR curves for the optimal Vs model at the SSP site, located in the eastern part of Jeju Island, as depicted in Figure 1. The observed HVSR curve showcased a notable peak at a frequency of 0.43 Hz, with a peak amplitude of 4.99, the highest among the nine sites examined in Table 4. For variance bounds ranging from 0.25 to 2.5, the misfit sizes of the inversion using the MC simulations varied from 338.41 to 1.38. Similarly, the SA algorithm yielded misfit sizes for the best-fit inversion model ranging from 205.04 to 1.24 within the same variance bounds. Although the peak amplitude near the resonance frequency closely matched between the observed and synthetic HVSR curves, the synthetic HVSR curve was slightly lower than the observed curve in the high-frequency range of 3-9 Hz. Figure 17 presents the Vs profile at the SSP site, illustrating all the inverted and optimal Vs models. In determining the optimal shear velocity profile, the darker regions, represent \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Layer**} & \multirow{2}{*}{
\begin{tabular}{c} **Lower Limit Depth of** \\ **Each Stratum (m)** \\ \end{tabular} } & \multirow{2}{*}{**Shear Velocity (m/s)**} & \multicolumn{3}{c}{RC} \\ \cline{4-5}  & & & **B (1–2)** & **B (2–3)** & **B (3–4)** \\ \hline
1 & 260–280 & 1000–1200 & \multirow{4}{*}{**(\(\cdot\)) 0.07**} & \multirow{4}{*}{**0.20**} \\
2 & **480–500** & **900–1100** & & & \\
3 & 680–700 & 1400–1600 & & & \\
4 & Bedrock & 2100–2300 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Depth, shear velocity (Vs), and RC of SGP site. Figure 16: Observed and synthetic HVSRs of SSP site; the red line indicates the observed curve, and the black dotted line indicates the synthetic curve. ing more frequently mapped areas, were given greater weight. The first layer, extending to depths of 40-60 m, formed a stratum with velocities of 900-1100 m/s. Employing the site classification method based on the outcrop shear-wave velocity, as indicated in Table 5, the outcrops at the SSP sites (900-1100 m/s) were categorized as S\({}_{\text{B}}\). The uncertainty associated with the first layer was notably larger than that of the subsequent deeper layers. The second layer extended to depths of 100-120 m, whereas the third layer, identified as the LVL with velocities of 600-800 m/s and a substantial velocity reduction of around 500 m/s, extended to depths of 320-340 m. With the further depth increase, the velocity doubled at depths of 460-480 m and 590-610 m, signaling the commencement of the deep basement [45]. The average RC values at the SSP site, as presented in Table 13, included four large positive values (0.10, 0.30, 0.10, and 0.22) and one large negative value (\(-\)0.26). The negative RC value of \(-\)0.26 indicates the presence of an LVL at this site, extending from 100-120 m to depths of 320-340 m. Additionally, with increasing the depth, the velocity rapidly doubled at depths of 460-480 m and 590-610 m, marking the onset of the deep basement. The final velocity model for the SSP site, as depicted in Figure 17, was interpreted as comprising six layers, inclusive of the deep basement. This interpretation was formulated by thoroughly analyzing both the frequently mapped models, represented by the darker-colored regions, and the average RC values. Most previous studies have posited that both the U-formation, of marine origin, and the Seoguipo sedimentary layer contribute to characteristics of low velocity, low