# Towards Automatic Landslide-Quake Identification Using a Random Forest Classifier
## 2 Study Materials and Method  
### Seismic Data  
The seismic data used belonged to the Broadband Array in Taiwan for Seismology (BATS), which was deployed by Academia Sinica and Taiwan's Central Weather Bureau (CWB) since 1992 [11]. BATS provides high-precision continuous seismic records to document the ground vibrations of a landslide. The array features 39 seismic stations comprising an intensive seismic network with a mean inter-distance of 30 km and a covering area of approximately 350 km by 400 km (Figure 1). All permanent BATS stations are equipped with state-of-the-art very-broadband sensors with a frequency band of 0.00833-8 Hz. Data streams with a sampling rate of 20 samples per s were recorded by the Q330 recorder. All stations are capable of internet connection for immediate retrieval of real-time data. In the study, we used the vertical component of seismic records. The seismic sensor in each station has its instrumental response. The website of the BATS provides information of the response of seismic sensors in each station. Since this study focused on massive landslides having a disturbed area larger than 10 ha on the island of Taiwan, the off-island stations were excluded and suitable stations with qualifying records were selected.  
Landslide-generated seismic waves (landslide-quakes) can be attributed to the shear force and loading on the ground surface as the mass moves downslope. The seismic amplitude gradually rises above the level from the ambient noise to the peak, exhibiting a cigar-shaped envelope. After the peak amplitude, most landslide-generated seismic signals experience relatively long decay times. In the frequency domain, landslide-quake energy is mainly distributed below 10 Hz, and the signature in the spectrogram appears triangular due to an increase in high-frequency constituents over the time [7; 8; 9]. The distinctive triangular signature in the spectrogram provides a great solution for differentiate the landslide-induced signals from those produced from the earthquakes and the ambient noise. Figure 1 presents the waveforms and spectrograms recorded from the catastrophic landslide with an area of 252 ha (the Xiaolin landslide) at 22:16, 8 August 2009, during Typhoon Morakot by four seismic stations. Similar seismograms and spectrograms of the Xiaolin landslide-induced seismic signals are recorded by the YULB and the YHNB stations, located 70 km and 185 km, respectively, away from the landslide, as shown in Figure 2a,b. However, the signals recorded by the RLNB (85 km) and TWKB (135 km) seismic stations, located amid the above mentioned stations, show undistinguishable fluctuations in association with this landslide event. These undistinguishable fluctuations can be explained by the seismic site effects or the disturbance of ambient noise from sea waves or human activities. The short-period (<10 s) ambient noise generated by sea waves is proved to influence all seismic records in the Taiwan island [12]. The TWKB station is located at the coastline and close to a famous sightseeing spot. The ambient noise from sea waves and the city is more significant. Byexamining whether each seismic station can clearly observe the characteristics of the seismic signals generated by the known massive landslides, eleven seismic stations, shown in Figure 1, were selected for the investigation.