## 4 Results
### Analysis of Anomaly Results of Earthquake Cases  
The best performing BILSTM prediction model was selected as the prediction algorithm after the error analysis of different algorithms and different prediction days. We then used the anomaly assessment method to study the Yangbi _M_s6.4-magnitude earthquake on 21 May 2021 and the Luding _M_s6.8-magnitude earthquake on 5 September 2022. The following graphs show the predicted results for two examples of earthquakes. The green curve shows the actual value; the red curve shows the predicted value; the blue curve shows the upper bound of the confidence interval; the light blue curve shows the lower bound of the confidence interval; and the red dashed line in the subplots indicates the difference between exceeding the upper bound and falling below the lower bound. Figure 8 shows that within the \(5^{\circ}\times 5^{\circ}\) area, 22 grid points, excluding grids points \(23.5^{\circ}\) N \(98.5^{\circ}\) E, \(24.5^{\circ}\) N \(101.5^{\circ}\) E, and \(26.5^{\circ}\) N \(98.5^{\circ}\) E, provided one to three cases of varying amounts outside the confidence interval in the month before the earthquake. Of these, 24 grid points were below the lower bound of the confidence interval, with the exception of the \(23.5^{\circ}\) N \(101.5^{\circ}\) E point, which was above the upper bound. The maximum value below the lower confidence interval was found at grid point \(27.5^{\circ}\) N \(101.5^{\circ}\) E, northeast of the epicenter. Therefore, we speculated that in the month before the Yangbi earthquake, anomalies of varying sizes were prevalent in the \(5^{\circ}\times 5^{\circ}\) area near the epicenter, dominated by those below the lower confidence interval. Figure 8 shows that most of the anomalies are below the lower bound of the confidence interval. To better illustrate how much the range was exceeded, the vertical coordinates in Figure 9 are negative upwards and positive downwards. Figure 9 shows that smaller-scale and smaller-range anomalies were observed during the two time periods from 25 April to 26 April and from 11 May to 12 May. A large-scale and more robust anomaly was observed from 5 May to 6 May, with the anomaly covering 17 grids, and the radiative energy of individual grid points was exceeded by up to \(42.27\) W/m\({}^{2}\), \(27.52\) W/m\({}^{2}\), \(23.58\) W/m\({}^{2}\), and \(23.11\) W/m\({}^{2}\). Therefore, we speculated that a strong and concentrated OLR anomaly existed 15 to 16 days before the Yangbi earthquake (5-6 May). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **5 Days** & **10 Days** & **15 Days** & **20 Days** & **25 Days** & **30 Days** \\ \hline ARMA & 625.0028 & 647.0955 & 835.6342 & 871.0932 & 882.8587 & 941.6699 \\ ARIMA & 718.1327 & 738.4042 & 2060.7494 & 1034.0422 & 1542.7989 & 928.8650 \\ SVM & 775.9093 & 784.3109 & 806.0665 & 1025.3715 & 1034.8680 & 1026.3374 \\ XGBoost & 640.0953 & 670.1815 & 773.8258 & 930.6856 & 964.0494 & 946.3818 \\ BILSTM & 619.2920 & 667.9708 & 734.5553 & 948.2177 & 947.8418 & 940.0596 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Total RMSE error of different time prediction models. Figure 8: Pre-earthquake OLR prediction and anomalies of the Yangbi _M_s6.4 earthquake\(-\)spatial dimension. Figure 10 shows that nine grid points did not exceed the confidence interval and were mainly located near the epicenter and to the east. Combined with Figure 1, it can be seen that the eastern part of the epicenter is the Chengdu Plain, which is at a lower elevation and has relatively inactive fault zone activity with fewer anomalies. The coexistence of anomalies above and below confidence intervals occurred at several grid points. The maximum value below the lower boundary occurs at the 28.5\({}^{\circ}\) N 100.5\({}^{\circ}\) E grid point southwest of the epicenter. Therefore, we speculated that the anomalies near the epicenter one month before the Luding earthquake were mainly distributed southwest and northwest of the epicenter.