# Retrospective Study on Seismic Ionospheric Anomalies Based on Five-Year Observations from CSES
## 4 Conclusions and Discussion  
This retrospective study of the CSES-01's observations during strong shallow EQs shows that the CSES-01 has the capability to detect ionospheric disturbances during seismic activity under quiet space weather, providing a valuable reference for earthquake monitoring from space. The main conclusions are summarized as follows:  
1. The observations from CSES-01 under quiet space weather conditions show that during the majority (over 90%) of the 47 shallow strong EQs (Ms \(\geq\) 7 and depth \(\leq\) 100 km), at least one payload captured certain abnormal signals; during more than 65% of these 47 EQ cases, two or three payloads onboard CSES-01 simultaneously recorded the ionospheric anomalies in multiple physical values; and during about 4% of these EQs, five or more payloads could simultaneously record multiple ionospheric disturbances. Additionally, the larger the magnitude, the more abnormal signals appear across multiple physical values;
2. The majority of anomalies recorded by different payloads onboard CSES-01 predominantly manifest within one week before or on the mainshock day, or occasionally appear about 11-15 days or 20-25 days before the mainshock;
3. Typically, the abnormal signals detected by the CSES-01 do not appear directly overhead the epicenter, but rather hundreds of kilometers away from the epicenter, and more preferably toward the equatorward direction;
4. For the different parameters analyzed in this study, the plasma density from LAP, the electromagnetic field in the ULF band recorded by EFD and SCM, and the energetic \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Payload** & **The Sensitive** & **Abnormal Phenomena** & **Anomalies Occurring** & **Anomalies Occurring** & **Anomalies Occurring** \\  & **Parameter** & & **Time** & **Position** \\ \hline  & & & Within 3 days before & \\  & & An increment with & the EQ; & 5–7 days and & East of the epicenter \\  & & 100\% amplitude change & 11–13 days before & & \\  & & & the EQ & & \\ \hline GOR & _NmF2_ & Abnormal increase in & 1–7 days before the EQ & Southeast of the \\  & & _NmF2_ & & & epicenter \\ \hline HEPP & Electron flux & An enhancement of & Within 5 days before & Northeast and east of \\  & & more than 0.5 & the EQ & the epicenter \\  & & magnitudes & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._electron in the lower energy band from HEPP show a relatively high occurrence of abnormal phenomena during the seismic activity period;
5. The anomaly recognition rates of seismic-related signals of payloads onboard CSES-01 vary: LAP, EFD, and SCM have the highest anomaly recognition rates, exceeding 70%; HEPP, HPM, and GOR have anomaly recognition rates of approximately 50%; and PAP has a low anomaly recognition rate of 24% due to contamination. In this study, the time window during which anomalies tend to be observed is relatively regular and consistent with previous studies (e.g., [3; 5; 6; 18]), based on the previous missions (e.g., the DEMETER satellite). However, the precise quantitative spatial locations of the anomalies are difficult to summarize, in most cases, they still fall in [PERSON]'s radius (or the magnetic conjugate points), which has been confirmed as the maximum distance from the earthquake epicenter [14; 16; 17]. The anomalies during the EQ period detected by CSES-01 are not located exactly over the epicenter but mostly away from the epicenter. Many previous studies also confirm that the disturbance does not occur directly above the epicenter but often shifts toward the equatorial direction and may also occur in the magnetic conjugate region [34; 42]. According to the LAIC, there are several coupling channels (e.g., [8; 16; 17; 18; 43; 44]). For example, in terms of the electric field, it is believed that the electric field caused by earthquakes will deviate toward the equatorial direction when it reaches the ionosphere along the magnetic field lines [16; 43].