## 4 Discussion  
### Identified Frequencies  
From a total of 11 records of seismic events, 12 frequencies are identified for the east-west direction, and 8 frequencies are identified for the north-south direction. Tables 5 and 6 show the performance of the methods in terms of the number of frequencies identified per direction. In the east-west direction for all dates, both the parametric and the nonparametric method algorithms succeed in identifying the frequencies. Moreover, the frequencies identified for each seismic event are similar between the two methods. For the north-south direction on 14 February 2011, the algorithms of the parametric method are not able to identify the frequencies, but the identified frequencies on the previous dates are similar. This allows us to assume that the programs achieve similar results. Similar frequencies are repeated on different dates. We assume that these represent the frequencies of the fundamental modes of vibration of the structure. A good way to compare these results would be to obtain the design frequencies of the structure. Figure 10 depicts the frequencies with the corresponding dates and their direction. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Frequencies [Hz]**} \\ \hline
**Date** & **CVA** & **PC** & **UPC** & **Bendat and Piersol \\ \hline
5 April 2010 & 2.42 & 2.41 & 2.45 & 2.44 \\
1 May 2010 & 2.51 & 2.51 & 2.37 & 2.44 \\
23 October 2010 & 0.69–3.37 & 0.70–3.44 & 0.70–3.41 & 0.68–3.42 \\
2 January 2011 & 0.69–2.61 & 0.69–2.64 & 0.69–2.64 & 0.68–2.63 \\
21 January 2011 & 2.62 & 2.63 & 2.62 & 2.63 \\
14 February 2011 & - & - & - & 0.69 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Identified frequencies in the north-south direction for the parametric and nonparametric methods. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Date** & **Direction** &
\begin{tabular}{c} **Frequency** \\ **[Hz]** \\ \end{tabular} & \(\xi\) **PC [\%]** & \(\xi\) **CVA [\%]** & \(\xi\) **UPC [\%]** \\ \hline
5 April 2010 & EW & 6.64 & 0.51 & 5.09 & 1.4 \\  & NS & 2.44 & 1.77 & 1.91 & 1.29 \\
1 May 2010 & EW & 3.22 & 0.7 & 2.24 & 1.65 \\  & EW & 3.91 & 1.25 & \(-0.55\) & 0.64 \\  & NS & 2.44 & 1.65 & 10.01 & 1.25 \\
23 October 2010 & EW & 6.74 & 1.7 & \(-0.04\) & 0.35 \\  & NS & 0.68 & 0.78 & 1.33 & 0.84 \\  & NS & 3.42 & 1.85 & 2.36 & 0.91 \\
2 January 2011 & EW & 2.64 & 2.37 & 2.85 & 1.45 \\  & EW & 3.42 & 1.8 & 2.98 & 4 \\  & NS & 0.68 & 2.61 & 1.8 & 2.1 \\  & NS & 2.63 & 2.35 & 3.24 & 2.35 \\
21 January 2011 & EW & 0.88 & 0.34 & 0.21 & 0.42 \\  & EW & 6.84 & 1.11 & 0.73 & 0.64 \\  & NS & 2.64 & 2 & 0.96 & 1.61 \\
14 February 2011 & EW & 2.64 & 2.02 & 1.12 & 1.48 \\  & EW & 3.14 & 14.67 & 1.65 & 0.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Damping for the parametric method algorithms according to date, direction of analysis, and identified translational frequency. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Frequencies [Hz]**} \\ \hline
**Date** & **CVA** & **PC** & **UPC** & **Bendat and Piersol \\ \hline
5 April 2010 & 6.59 & 6.55 & 6.57 & 6.64 \\
1 May 2010 & 3.15–3.88 & 3.21–3.87 & 3.22–3.94 & 3.22–3.90 \\
23 October 2010 & 0.84–1.14–6.60 & 0.85–1.14–6.75 & 0.86–1.10–6.72 & 0.88–1.07–6.74 \\
2 January 2011 & 2.68–3.33 & 2.62–3.36 & 2.61–3.41 & 2.63–3.42 \\
21 January 2011 & 0.86–6.86 & 0.86–6.86 & 0.85–6.84 & 0.88–6.84 \\
14 February 2011 & 2.60–3.13 & 2.64–3.20 & 2.61–3.24 & 2.64–3.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Identified frequencies in the east-west direction for the parametric and nonparametric methods. We note an interesting trend concerning the identified frequencies--the mass and stiffness of the building change during the construction period.