## 3 Data Preprocessing Methods  
The ionosphere is easily disturbed by various natural and artificial sources, such as the geomagnetic storms that mainly originate from the Sun or the inner magnetosphere, the intense lightning activity generated from the atmosphere, or the artificial VLF radio waves emitted by powerful terrestrial transmitters. Therefore, before searching for the seismic information from the satellite data, it is necessary to eliminate any possibilities from all other non-earthquake sources. Several data preprocessings are routinely operated to avoid non-EQ disturbance sources.  
Step 01: Data cleaning, through which the orbit data affected by satellite control operations or the other artificial experiments are directly excluded, according to the health condition data of the platform and payloads.  
Step 02: Space-weather condition check. Compared to the disturbance induced by the solar wind, geomagnetic storms, or lightning activities, the influence from earthquakes is relatively feeble. Under the disturbed space-weather conditions (Dst \(\leq-30\) nT or Kp \(\geq 3\)), we usually do not analyze the seismo-ionospheric disturbances. That does not mean it is impossible to extract seismic signals under disturbed space-weather conditions. As the physical processes of the seismo-ionospheric phenomena are still poorly understood, selecting the quiet space weather condition can avoid many complicated factors. Additionally, as most previous studies have carried out, we mainly focus on the nighttime data to avoid the complicated ionospheric ionization effects in the daytime.  
Step 03: The EQ influential area selection. According to the empirical equation of the earthquake preparation zone put forward by [PERSON] et al. [28], the influential zone of an earthquake is roughly computed by the equation R = 10\({}^{0.43\text{M}}\), where R is the diameter of the influential earthquake zone in the km scale, and M is the magnitude of the EQ. For convenience, considering the projection feature of a satellite orbit on the ground, we choose a square area, that is, the epicenter \(\pm\) 5\({}^{\circ}\) area for a magnitude 6 EQ and epicenter \(\pm\) 10\({}^{\circ}\) for a magnitude 7 EQ.  
Step 04: Frequency band selection is essential for preprocessing electromagnetic data. The electromagnetic field or waves can be easily interrupted by parasitic signals or other interference sources, which cause uncertainties or errors. For example, below 200 Hz, the interferences originating from instruments or satellite platforms, such as electrostatic turbulence from solar panels or magnetic torque, must be carefully excluded [12]. Selecting a frequency range free of artificial interferences is essential before searching for seismic-related emissions. According to the calibration tests in orbit, at the frequency of 27.5 Hz and its harmonics (from 2 to 5 times and 8-12 times), the SCM data are influenced by the magnetic torque that generates a magnetic moment to maintain the satellite platform position. Over the equatorial area, the electric field data in ULF/ELF/VLF bands are interfered with by the internal communication signals of the satellite platform.