## 3 Study Case and Method
### Seismic Data Processing  
In this study, the seismic data recorded by broadband seismic stations were collected from the Broadband Array in Taiwan for Seismology (BATS), which was deployed by Academia Sinica and Taiwan's Central Weather Bureau (CWB) since 1992 [22]. BATS provides high-precision continuous seismic records to document the ground motions of landslides. All permanent BATS stations are equipped with broadband sensors with a frequency band of 0.00833-8 Hz. All stations are capable of internet connection for immediate retrieval of real-time data. The high-energy seismic signals generated by the Taimali landslide were detected by 15 three-component broadband seismometers (Figure 3), including the nearest station, MASB, at a distance of 19 km, and the farthest station, KMNB, at a distance of 325 km. Even in the Taiwan Strait, the seismic signals caused by the landslide could be detected by the PHUB and KMNB stations on small islands.  
The ground motion induced by the Taimali landslide can be observed in the seismic record at the MASB station (Figure 4a). However, it is not easy to determine the initiation time and end time of an event by observing complex time-domain waveforms. Therefore, a time-frequency spectrogram and a spectrum were obtained through the fast Fourier transform (Figure 4b,c). In the seismic record, the event initiated after 30 s and terminated at around the 210 th second. From the spectrum, the presence of distinct low-frequency and high-frequency components was apparent. The values f = 3.0 Hz and f = 0.5 Hz were taken as the representative frequency of the signal in the high-frequency and low-frequency ranges, respectively. Several wave packets can be observed in the two filtered waveforms  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Zone**} & \multicolumn{1}{c}{**Area (\(10^{6}\) m\({}^{2}\))**} & \multicolumn{1}{c}{**Maximum**} & \multicolumn{1}{c}{**Average**} & \multicolumn{1}{c}{**Volume**} & \multicolumn{1}{c}{**Estimated**} \\  & & Thickness (m) & Thickness (m) & (10\({}^{6}\) m\({}^{3}\)) & Mass (10\({}^{6}\) kg) \\ \hline
1 & 0.93 & 219.7 & 80.9 & 75 & 20 \\
2 & 1.24 & 196.9 & 96.9 & 45 & 12 \\
3 & 1.22 & 110.6 & 67.2 & 43 & 12 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Measurements of the source area and the deposit areas.  
Figure 2: The map of the source area and the deposit areas of the Taimali landslide. The source area is marked by the blue line. The deposit areas are marked by red lines.  
(Figure 4d,e), which indicates the event experienced several stages of movement. [PERSON] et al. [8] proposed an empirical formula to evaluate landslide seismic magnitude (L\({}_{\text{m}}\)) and reported that the L\({}_{\text{m}}\) of the Taimali landslide was 4.3.  
The seismic data were processed by deconvolving the instrument response, integrating the seismic records from ground velocity to displacement, and resampling seismic data from 20 to 1 Hz. Then the horizontal components of the seismograms of each station were rotated from the north and east directions to the radial and transverse directions. The radial direction refers to the direction from the seismic source to the station, and the transverse direction is perpendicular to the radial direction. The processed signals were filtered by a fourth-order Butterworth band-pass filter with a corner frequency of 0.01-0.033 Hz. Finally, the seismic data were weighted according to the signal-to-noise ratio (SNR). SNR was calculated by dividing the maximum of the absolute amplitude by the mean of the absolute amplitude of the seismic waveform.  
Figure 3: Original displacement seismographs of the Taimali landslide.