## 5 Discussion
### Risk Assessments
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Single Fault Model**} & \multicolumn{3}{c}{**Multifault Model**} \\ \cline{2-6}  & **Initial Setting** & **Modelled Fault** & **Initial Setting** & **Modelled Fault 1** & **Modelled Fault 2** \\ \hline Fault length (m) & 10,000–53,000 & 51,140.7 & 3000–25,000 & 26,417.9 & 24,985.5 \\ \hline Fault width (m) & 4500–8000 & 4567.42 & 1500–4000 & 1639.47 & 1987.89 \\ \hline Fault depth (m) & 100–12,000 & 4409.97 & 100–12,000 & 1394.25 & 1781.54 \\ \hline Dip angle (deg) & 32.0–60.0 & 35.43 & 35.0–60.0 & 57.46 & 59.45 \\ \hline Strike angle(deg) & 150–200 & 183.79 & 150–200 & 188.87 & 184.97 \\ \hline Center x(m)* & 4000–8500 & 4002.75 & 2000–10,000 & 4374.67 & 4000.72 \\ \hline Center y(m)* & 12,000–21,000 & 20,657.42 & 3000–18,000 & 8941.41 & 9294.90 \\ \hline Center of fault & & E 129.392 & & E129.396 & E129.392 \\ (deg) & & N 35.748 & & N 35.642 & N 35.646 \\ \hline Strike slip(m) & \(-\)0.1–0.1 & 0.0993 & \(-\)0.3–0.3 & 0.292 & 0.285 \\ \hline Dip slip(m) & \(-\)0.3–0.3 & \(-\)0.140 & \(-\)0.5–0.5 & 0.492 & \(-\)0.373 \\ \hline \multirow{2}{*}{Fitness} & Ascending: RMSE 0.010, Stddev 0.008 & \multicolumn{3}{c}{Asending: RMSE 0.011, Stddev 0.014} \\  & Desending: RMSE 0.017, Stddev 0.01 & \multicolumn{3}{c}{Desending: RMSE 0.015, Stddev 0.012} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Initial parameter settings for GBIS modelling and modelled values. with the available information, quantitative hazard assessment employing probabilistic approaches is further proposed. Seismic hazard assessments are normally conducted by either deterministic seismic hazard assessment or PSHA [74]. As deterministic seismic hazard assessment considers a small number of source scenarios and the largest ground motion, it does not fit with the case of this study. On the contrary, PSHA includes all possible scenarios and computes the synthesized probability of certain thresholds of ground motion. Considering the uncertainty of the earthquakes that may be induced by the Ulsan fault line, we employed PSHA and its S/W implementation, called the R-CRISIS ([[http://www.r-crisis.com/](http://www.r-crisis.com/)]([http://www.r-crisis.com/](http://www.r-crisis.com/))) [75; 76] to extract a potential hazard map. Combined with the seismic source extracted from the GBIS model (Table 5) and the historical earthquake record around the Ulsan fault line (Figure 11a), which was integrated into the Gutenberg-Richter model [77], we calculated the risk map around the Ulsan City area, as demonstrated in Figure 11b-d. Note that the modified Gutenberg-Richter method [78] implemented in R-CRISIS establishes a seismicity model associated with occurrence probability of earthquake of considerable magnitudes within a certain frame time period. In this study, the time frame was established as 50 years, considering the recurrence time period of the major earthquakes in the target area. This may have some implications on the potential activation period of the Yangsan-Ulsan faults, but is not strongly supported by the ground works owing to absence of long-term study of the Yangsan-Ulsan faults. Thus, our risk assessment needs to be considered as a case study based on the scenario to assess the potential risk, rather than a robust estimation. The risk maps represented by the intensity values in a 10% exceedance probability demonstrated that (1) all industrial parks, in particular UPC, belong to the highest risk area; (2) the peak time of seismic risk is around ten years, as shown in Figure 11c. Regarding the confidences of modelled parameters employed for the risk assessment, it is worth noting that the recent active fault studies [31; 79] around Ulsan reconstructed the migrating structure similar to this study. Thus, the PSHA outcomes in this study can be used for future safety planning as well as the establishment of new industrial regulations.