## 3 Results and Discussion
### Multi-Channel Anomalies  
To improve the accuracy of earthquake prediction, we scan the relative power spectrum data in the four channels and identify the region of four-channel anomalies, which means the region where all of the four channels are abnormal at the same time. The statistical  
Figure 16: Power spectrum images on 7 July 2019.  
Figure 17: The cover area of the anomalies before and after Tibet earthquake.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Channel**} & \multirow{2}{*}{\begin{tabular}{c} **Start Time** \\ **(Days)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **End Time** \\ **(Days)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Maximum** \\ **Maximum** \\ **(Days)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Time of** \\ **(Days)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Maximum** \\ **(Cover Area)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Distance** \\ **(km)** \\ \end{tabular} } \\ \hline IR1 & \(-10\) & \(-6\) & 25.8302 & \(-10\) & 2366 & 11.4747 \\ IR2 & \(-10\) & \(-6\) & 21.7490 & \(-7\) & 2569 & 11.4747 \\ IR3 & \(-11\) & \(-5\) & 17.1277 & \(-9\) & 3147 & 11.4747 \\ IR4 & \(-30\) & \(-20\) & 36.5649 & \(-25\) & 7125 & 184.2958 \\ IR4 & \(-11\) & \(-5\) & 35.2557 & \(-9\) & 3237 & 11.4747 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The spatial–temporal characteristics of anomalies before the Tibet earthquake.  
result is shown in Table 6. A larger distance threshold can improve PPV and TPR, but can not improve the probability gain. The probability gain is the highest when the distance threshold is 200 km. Figure 18 shows the comparison between the PPV, TPR and gain of multi-channel methods with that of the single-channel method with the distance threshold of 200 km. The PPV and probability gain of the multi-channel method are higher than that of any single-channel method. In particular, the probability gain is roughly doubled, although the TPR is very small. Only 19 earthquakes are associated with the multi-channel anomalies because the multi-channel method only considers simultaneous anomalies of four channels, and earthquakes with anomalies of no more than three channels will be missed. The locations of the epicenters of these 19 earthquakes are shown in Figure 19. Four-channel infrared anomalies were found before the earthquakes in different regions, which indicates the phenomenon is not only suitable for a specific region. The distribution of anomaly time is shown in Figure 20. Eight earthquakes occurred one to two weeks after the anomalies appeared. Only one earthquake occurred three to four weeks after the anomaly appeared. Figure 21 is the Molchan diagram of the different methods. The spatiotemporal occupancy of the four-channel anomaly is much smaller than that of the  
To compare the multi-channel method with other methods, the authors, data, study region, study period, earthquake magnitude and their results in previous studies are shown in Table 7[23; 28; 29; 31; 46]. The anomaly time means the number of days from anomaly to earthquake. The multi-channel method could obtain the highest probability gain, although the TPR is the lowest. This means that this method reduces the uncertainty of earthquake prediction more obviously than other methods. The PPV of the multi-channel method is also the highest in the studies on earthquakes of magnitude five and above. It means that the multi-channel method has higher accuracy in earthquake prediction than previous methods for earthquakes with magnitude five or above.