## 4 Seismic Hazard Analysis
More accurate determination of the local soil conditions and regional seismicity generally provides more realistic building designs and assessments [71; 72; 73]. Ground motion amplification to account for local soil and site effects is established through a constant soil factor, which uniformly increases the normalized elastic response spectra in all periods [74]. In the previous seismic design code, soil classes and soil groups were expressed only as local soil classes together with the updated code, and six different local soil classes were expressed. Here, an average local soil type was selected as the ZC type given in TBEC-2018 (very dense sand, gravel, hard clay layers, or weathered rocks with many cracks) [31] to make comparisons. The characteristics of this soil type (ZC) are given in Table 7. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Local Soil Class**} & \multirow{2}{*}{**Soil Type**} & \multicolumn{4}{c}{**Upper Average at 30 m**} \\ \cline{3-6}  & & **(Vs)30 (m/s)** &
\begin{tabular}{c} **(N60)30** \\ **(Pulse/30 cm)** \\ \end{tabular} & **(cu)30 (kPa)** \\ \hline \multirow{2}{*}{ZC} & Very tight sand, gravel, and & & & \\  & hard clay layers or weathered, & & & \\  & very cracked weak rocks & & & \\ \hline \multirow{4}{*}{ZC} & Local ground coefficients (F\({}_{\text{s}}\) and F\({}_{\text{1}}\)) were used for the first time with the current code. The local soil effect coefficient F\({}_{\text{S}}\) and local soil effect coefficient for a 1.0-s period (F\({}_{\text{1}}\)) for the ZC soil type are given in Tables 8 and 9, respectively. & \\ \cline{1-1} \cline{2-6}  & Local soil coefficient F\({}_{\text{S}}\) for the short period zone for ZC [31]. & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Local soil class type ZC [31]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Local Soil Class**} & \multicolumn{4}{c}{**Local Ground Effect Coefficients (F\({}_{\text{s}}\)) for ZC Class**} \\ \cline{2-6}  & \(\mathbf{S_{S}\leq 0.25}\) & \(\mathbf{S_{S}=0.50}\) & \(\mathbf{S_{S}=0.75}\) & \(\mathbf{S_{S}=1.00}\) & \(\mathbf{S_{S}=1.25}\) & \(\mathbf{S_{S}\geq 1.50}\) \\ \hline ZC & 1.30 & 1.30 & 1.20 & 1.20 & 1.20 & 1.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Local soil coefficient F\({}_{\text{S}}\) for the short period zone for ZC [31]. The horizontal and vertical elastic design spectra were obtained for various recurrence periods in each province. Here, the amplification factor of the soil was assumed to be constant (~1.5). However, soil nonlinearity plays an important role in defining soil factors, especially in soft soils. The amplification of soft soils is higher than that of hard soils. The soil type and soil nonlinearity affect the definition of seismic hazards and the response of the structure [75]. The presence of soil nonlinearity highlights the inaccuracy of using constant soil factors for sites with different seismic hazards [76]. Probabilistic seismic hazard analyses are usually performed with quasi-experimental ground motion models from global databases, where the average source, path, and site effects are valid for a particular area of interest. The site-specific site response differs from the global average based on the seismic velocity and basin depth field parameters used in ground motion models [77]. The comparison of the horizontal and vertical elastic design spectra obtained are shown in Figures 5 and 6, respectively. Unlike the previous  
As mentioned before and seen from the design spectra, the Bingol province has the highest risk in the studied region. Thus, we compared the spectra with different probabilities of exceedance in 50 years, which are defined in TBEC-2018 (Figure 7). Although there were some differences in the spectral acceleration values, similar curve characteristics were obtained for other provinces. The magnitude of the expected earthquake increased when the probability of exceedance decreased.