# Retrospective Study on Seismic Ionospheric Anomalies Based on Five-Year Observations from CSES
## 3 Results
### An Example of EQ Case Analysis  
Here, we take a very significant earthquake event that occurred in Turkiye on February 6 as an example to introduce the process of analyzing seismic ionospheric anomalies. This strong earthquake included double shocks that occurred consecutively within a day. The first one, with a magnitude of 7.8, occurred at the local time of 4:17 a.m. (1:17 UTC), centered about 70 km from Gaziantep, in Sekeroba (37.15\({}^{\circ}\)N, 36.95\({}^{\circ}\)E, with a focal depth of 20 km); the second one, with a magnitude of 7.8 occurred 100 km north of the first epicenter, in Ekinozu (38\({}^{\circ}\)N, 37.15\({}^{\circ}\)E, focal depth 20 km) at the local time of 1:24 pm [40]. This sequence of earthquakes caused widespread damage and resulted in tens of thousands of casualties in Turkiye and Syria. The bilateral rupture propagation of both mainshocks across multiple fault segments was observed [40]. Figure 4 displays the epicenters of the double EQs in Turkiye (red stars) and the EQ influential zone (magenta dashed range), which covers around a 10\({}^{\circ}\) (latitude) \(\times\) 10\({}^{\circ}\) (longitude) area, computed using the equation of Dobrovolsky [14]. The orbit trajectories of CSES-01 (blue curves) within this influential zone, spanning from 25 days before to 5 days after the mainshocks, are shown in the enlarged image (the black sector boundary), where the red stars represent the epicenters, and the magenta dashed range shows the influential zone (10\({}^{\circ}\)\(\times\) 10\({}^{\circ}\)). The blue curves illustrate the ascending orbit (nightside) trajectories of the CSES-01 satellite. By using the running quartile method based on the selected data presented in Figure 4, the variation in electron density (\(Ne\)) and oxygen ion density (\(N_{O+}\)) from 11 January to 9 February over the EQ influential zone are illustrated in Figure 5. From top to bottom, the panels display the space weather indexes (\(Kp\) and \(Dst\)), \(Ne\), the variation amplitude (%) of \(Ne\), \(N_{O+}\), and the variation amplitude (%) of \(N_{O+}\). The red vertical lines in all panels mark the mainshock time of the EQ. In the first panel, the blue bars represent the \(Dst\) index, and the green curves correspond to the \(Kp\) index, while the red horizontal dashed lines represent the value of \(Kp=3\). In the second and fourth panels, the current variation trend of \(Ne\) and \(N_{O+}\) is depicted as blue curves, while the background trends (i.e., median values) are represented by black curves; the upper and lower boundaries are shown as pink curves. In the third and fifth panels, the blue lines represent the change amplitude (%) of \(Ne\) and \(N_{O+}\), and the red horizontal dashed lines represent the variation amplitude of 50% and -50% respectively, which are the criteria for identifying possible seismic anomalies of plasma density based on previous research experience [15]. It is observed that an unusual synchronous increase in \(Ne\) and \(N_{O+}\) occurred on 27 January (marked by red ellipses, 10 days before the EQ) under quiet space weather conditions, indicating a possible link to the EQ. The other two sets of abnormal increases before the EQ and one increase after the  
Figure 3: The distribution of global shallow, strong EQs with a depth \(\leq\) 100 km and Ms \(\geq\) 7 occurred from February 2018 to February 2023. EQ (marked by green rectangles) were primarily associated with space weather conditions, as evidenced by the space weather index presented in the first panel of Figure 5.  
We calculated difference maps of the magnetic field above the EQ influential zone every 5 days (matching the recursive period of CSES-01) to extract the magnetic field fluctuations  
Figure 4: The orbit trajectories of CSES-01 data selected for the Türkkiye EQs on 6 February 2023. The red stars represent the epicenters, and the magenta dashed range shows the potential influential zone (\(10^{\circ}\times 10^{\circ}\)).