## 4 Full-Scale Measurement of the Canton Tower  
To further validate the MEMD-based approach for a nonstationary process, the acceleration data of the Canton Tower during the Heyuan earthquake are used in the present study. The Canton Tower, a 610 m tube-in-tube structure, was installed with a long-term structural health monitoring system comprised of more than 700 sensors, including 20 accelerometers [41], as shown in Figure 10. Since its constructive period, the monitoring system records rich data on the temperature, wind speed and dynamic performance of the structure during ambient excitation and several hazard events. More details can be referred to in [PERSON] et al. [41; 42]. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Mode**} & \multirow{2}{*}{**FEM**} & \multirow{2}{*}{**HHT**} & \multicolumn{3}{c}{**FBFFT**} & \multicolumn{3}{c}{**MFBFFT**} & \multirow{2}{*}{**SSI**} & \multirow{2}{*}{**MSSI**} & \multirow{2}{*}{**ERA**} \\ \cline{3-3} \cline{5-10}  & & & **MPV** & **COV** & & **MPV** & & **COV** & \\ \hline
1 & 3.80 & 4.68 & 4.353 & 2.3\% & 4.322 & 2.1\% & 4.126 & 4.138 & 3.56 \\
2 & 14.43 & 15.50 & 14.558 & 1.0\% & 14.560 & 1.7\% & 14.892 & 14.664 & 14.08 \\
3 & 27.82 & 26.52 & 27.936 & 0.7\% & 28.020 & 0.7\% & 28.031 & 28.009 & 27.18 \\
4 & 41.61 & 38.98 & 40.392 & 1.1\% & 40.228 & 0.2\% & 40.570 & 40.197 & 40.37 \\ \hline MARD & - & 10.4\% & 4.7\% & - & 4.7\% & - & 3.8\% & 3.4\% & 3.5\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Identified results of the natural frequencies (Hz) for the shaking table test. Figure 9: Stabilization diagram of original and decomposed acceleration response for the shaking table test. (**a**) Original data; (**b**) IMF10. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Mode**} & \multirow{2}{*}{**HPBW**} & \multirow{2}{*}{**HHT**} & \multicolumn{3}{c}{**FBFFT**} & \multicolumn{3}{c}{**MFBFFT**} & \multirow{2}{*}{**SSI**} & \multirow{2}{*}{**MSSI**} & \multirow{2}{*}{**ERSA**} \\ \cline{3-3} \cline{5-10}  & & & **MPV** & **COV** & & **MPV** & & **COV** & \\ \hline
1 & 6.53\% & 4.54\% & 4.44\% & 36\% & 3.65\% & 38\% & 6.72\% & 4.32\% & 5.93\% \\
2 & 4.35\% & 4.93\% & 2.89\% & 23\% & 4.67\% & 19\% & 7.20\% & 6.73\% & 4.14\% \\
3 & 2.59\% & 3.52\% & 3.76\% & 16\% & 3.47\% & 17\% & 4.10\% & 3.73\% & 3.69\% \\
4 & 1.51\% & 2.64\% & 2.60\% & 18\% & 2.69\% & 19\% & 2.70\% & 3.54\% & 2.66\% \\ \hline MARD & 28.4\% & 3.7\% & 15.6\% & - & 10.2\% & - & 23.3\% & 21.6\% & 10.9\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Identified results of the damping ratios for the shaking table test. The Heyuan earthquake, a 4.2-magnitude quake, occurred at 13:50 on 31 August 2012. The epicenter was only about 160 km away from the Canton Tower which was a typical short-distance earthquake for the structure. The acceleration responses recorded from 13:00 to 14:00 were utilized for extracting the modal parameters. The acceleration time histories atop the Canton Tower during the earthquake are shown in Figure 11. The maximum acceleration response at section 8 of the tower is only 0.53 milli-g due to the small magnitude of the quake. As shown in Figure 11, the strike instance of earthquake is reflected as a spike in the one-hour acceleration history. Since the paper is focusing on the modal identification method under the nonstationary excitation, it is reasonable to take Canton Tower with the Heyuan earthquake as an example to demonstrate the proposed MEMD-based modal identification method. The selected time histories recorded by the X-direction sensors and the Y-direction sensors were decomposed by the MEMD method independently. The vibration modes of Canton Tower are quite complex and close [43], and the original responses are mainly divided into 13 component IMFs in which the vibration modes are not perfectly decomposed. Fortunately, the mode mixing of the selected segment exists only in higher modes which provides a reasonable estimation of the first several modes.