## 3 Automatic Detection Method
Black dots stand for earthquakes occurred before the automatic detection method is used, brown ones for aftershocks occurred on 25–30 January 2024 after the detected ionospheric perturbations on February 2024 but probably affected by solar activities, and red dots for ones took place after the detected effective ionospheric perturbations on 3 February 2024. The automatic detection method was put into earthquake prediction service immediately after this Wushi \(M_{\rm S}\) 7.1 event to mainly trace nighttime electron density weekly, as well as the ion (O\({}^{+}\)) density as a comparison, to monitor possible precursory signals during impending aftershocks. The electron density is considered as the dominant parameter during this period due to the contaminated sensors on the PAP payload one month after the CSES launch [35], while positive results from this payload have been reported [23; 24; 35]. Therefore, it is believed that the corresponding ion perturbations and electron ones are more reliable if one earthquake is detected at the same time by these two parameters [34]. One point is that perturbations with an amplitude less than 10% are generally ignored due to their variations being merged into the background irregularities of the ionosphere [27] when this method is utilized in earthquake prediction practice. While perturbations where this parameter is beyond 20% are usually considered more reliable during this period, it is possible that seismic activities can induce variable amplitude disturbances. Another point is that only perturbations lying in a latitude range of 15-55\({}^{\circ}\)N and longitude range of 70-135\({}^{\circ}\)E in an area covering all of China are displayed in different colors of grey for referable ones with a amplitude of 10-20% and blue for reliable ones > 20% in the weekly map. Figure 4: Weekly distributions of plasma perturbations detected automatically by the software prior to the biggest aftershock of the Wushi \(M_{\rm S}\) 7.1 earthquake on 23 January 2024. Grey triangles denote ionospheric variations with a magnitude of 10–20%. The green empty triangle stands for the detected obvious electron perturbation with a magnitude 38.3%. It is first considered as possible precursory information and then confirmed to be a plasma bubble induced by solar activity. The night orbit 33175 on which this disturbance occurs has been displayed by the measured values of the electron density with different colors, and the remarkable plasma bubble can be easily distinguished. The ground-based Hongqian observing station is presented as a black rectangle. Blue triangles for magnitudes exceeding 20% (24.6% for the electron density and 27.3% for the ion density) have been testified as precursors of the impending biggest aftershock of the Wushi \(M_{\rm S}\) 7.1 earthquake. The red dot stands for the location of the biggest aftershock of \(M_{\rm S}\) 5.8 of the Wushi earthquake sequence. (**a**) During 24–30 January 2024; (**b**) during 31 January–6 February 2024; (**c**) during 7–13 February 2024; and (**d**) during 14–24 February 2024. Figure 4 demonstrates the ionospheric perturbations searched automatically via the software week by week from 24 January 2024 after the Wushi main shock to 24 February 2024, one day before the biggest aftershock of \(M_{\rm S}\) 5.8 on 25 February 2024. A plasma perturbation on the electron density was first detected successfully during 24-30 January 2024, and it is shown in Figure 4a as an empty green triangle. Its related information has been listed in Table 3 as Pe1. From Table 3, it is obvious that this ionospheric irregularity took place on 24 January 2024, in night orbit 33175 with an increased amplitude of 38.3%, which can be considered as a precursory variation because its magnitude was more than 20%. But no ion perturbations were searched at the same orbit, or none at the other orbits covering the considered area in this investigation.