## 4 Case Analysis of Concepcion Earthquake
### Ionospheric Structure Anomaly before Earthquake
The results are shown in Figure 12. At 100 km, the distribution of RO events with drastic variations has no special rule. This may be related to the sporadic E-layer signatures or frequency collisions of electrons with a high-density neutral atmosphere. The imitation of the Abel inversion is another potential cause. The error accumulates as the profile goes to lower altitudes. Figure 12a shows what may be an effect of the error in the inversion process [42]; at the height of 200 km and 300 km, the electron concentration anomalies are consistent with the abnormal changes in the F2 layer. The vertical ionospheric structure is affected by the change in longitude and latitude. Especially for events with an extensive variation range, they are concentrated in the south area near the epicenter, slightly different from those in Figure 9. Generally, by the interaction of each ionization, the prominent long-wavelength fluctuation when traveling induced the amplification of the AGW effect in the F2 layer. The observation of the obvious local oscillation between 200 and 300 km in height here further confirms the idea. With the increase in height, the energy of the acoustic gravity wave gradually attenuated and the upper ionosphere gradually returned to a normal state. Figure 11: Vertical ionosphere structure near the epicenter on February 25 recorded from Proff#4–9. The ionospheric profiles in the disturbance and quiet periods and their color map are described in the left, middle, and right panels, respectively. In a specific coupling way, the satellite records the complex changes of the ionosphere over the seismogenic area. In [43], the \"Lithosphere-atmosphere-ionosphere coupling\" system was proposed to find convincing evidence of the ionosphere effect. At present, there are three main pathways of Lithosphere-Atmosphere-Ionosphere Coupling [44; 45; 46; 47; 48; 49; 50]: chemical, electromagnetic, and acoustic. The chemical pathway mainly refers to the influence of changes in geochemical parameters (gas or radon diffusion, change of water level, etc.,) on the ionosphere. Such abnormal phenomena are caused by gas release before the earthquake. Under the action of the crustal stress accumulation, the gas released from the fractured anode pore scatters to the surface. The ionization process is then activated to form the hydrated ion clusters at aerosol size (1-3 um) during ion-induced nucleation [1]. Based on the aerosol optical depth (AOD) database, the abnormal aerosol changes of the event were detected [41]. The radioactivity of the aerosol ion clusters causes neutral gas ionization. Consequently, the physical properties and electrical balance  
Figure 12: Ionosphere anomaly in multiple heights over the earthquake area of the Concepcion earthquake on February 25. (**a–e**) represent the ionosphere disturbances at different heights of 100–500 km, respectively, where the focal sphere represents the epicenter. change by ion introduction in the local atmosphere. The reaction leads to increasing or decreasing conductivity [51]. The electromagnetic path mainly refers to the low-frequency electromagnetic radiation caused by the microstructure of rocks or by electromagnetic noise in the seismogenic area. The inducement is produced by the release of electric charge onto the fracture surface of the seismic source and affects the ionosphere [46]. These electromagnetic signals propagate along with the atmospheric boundary layer and penetrate the orbit height of the satellite, which is directly recorded by the satellite. The recording of the electromagnetic signal before the Concepcion earthquake was completed by the Demeter satellite [52; 53]. In the near-earthquake stage, there was a noise band in the electric field radiation of the VLF near the epicenter, and the radiation appeared in the cross of magnetic conjugate region along the magnetic field line. The strong electric field radiation affects the plasma distribution in the ionosphere [54].