## 4 Case Analysis of Concepcion Earthquake
### Ionospheric Structure Anomaly before Earthquake
These two coupling paths, shown in Figure 13, were detected early by the remote sensing satellite (Terra/Aqua) and the electromagnetic satellite (DEMETER), respectively [39; 52]. The acoustic coupling path was further observed based on the data of the COSMIC occultation. Because of the NOAA/AVHRR satellite thermal images in operation, the infrared excitation from the earth's crust in Northeast China with the largest linear structures and fault system was captured. The double variations of CO\({}^{2}\) concentration and the increase in temperature of about 3\({}^{\circ}\) were subsequently recorded. The greenhouse gases excited the acoustic-gravity waves, and the changes in the intensity of the optical ionospheric glow lasted dozens of minutes. Coincidentally, the ionospheric disturbances appeared with spatial and temporal scales, corresponding to the spectrum of AGW excitation. In the RO observations, the seismicity influence on the ionospheric anomaly in the F region by AGWs is expected to be confirmed. According to the 3D numerical model of the excitation of AGWs [10], the lithospheric gas source and propagation into the ionosphere were investigated. If a bell-shaped lithospheric gas source is characterized with the dimensions of 100 \(\times\) 100 km\({}^{2}\), the AGW  
Figure 6:0 Seismic multi-channel coupling before the Concepcion earthquake. excitation can cause a maximum change in the F region over 70 min. The peaks of the AGW wavelength and relative variations to the electron density (Ne) then reach dozens of km and percentage points, respectively. In Figures 10 and 11, the vertical ionosphere structure has a large vibration, covering from the bottom to the upper ionosphere. The oscillation amplitude increases with the uplift of height in a similar effect as the acoustic gravity wave. A clear feature set of the RO fluctuation, namely, a duration of around 1 h (14-15 UTC), a wavelength length of \(>\)50 km, a location at the F layer, and a relative variation (\(\delta>0.5\)), is consistent with these AGW descriptions. On this basis, we infer that the dissemination of the lithosphere's rupture may induce the acoustic gravity wave upward to the atmosphere. The reactions alter the temperature and density of the plasma layer and the subsequent structural damage of the ionosphere. Therefore, the ionosphere anomalies can also be characterized for AGWs in observed profiles prior to quakes, in addition to after the event. Moreover, AGWs can even be responsible for the change in electromagnetic wave characteristics in the \"Earth-Ionosphere\" waveguide. Today, plasma instability caused by AGWs excited by lithospheric gas is still worth studying. To satisfy the unified physical phenomena observed before earthquakes, different channels are under development in statistical cases and specific quakes. If RO profiles are amassed (the COSMIC-2 system in full operation), the time series at each profile location will further confirm the AGW coupling. If the development of the AGW effect is analyzed in time, we may find the outlier fluctuation of the electron density over the seismically active area in the transmission process of the upward AGW waves. A similar response can be evidenced by TEC variations from GIMs prior to the Concepcion earthquake in Figure 6:1  
Figure 6:2 PEIA response by GIM. (**a**) The ionospheric TEC maps and (**b**) TEC anomalies near epicenter 15 days before shocks. (**c**,**d**) is the regional TEC anomalies near the epicenter from UT 10:00–12:00, February 21 and UT 08:00–10:00, February 25, respectively. The TEC anomalous variations before the Mw 8.8 Concepcion earthquake on 27 February 2010, were analyzed. As shown in Figure 14, the highest daily total electron content usually occurs from universal time (UT) 16:00 to UT 20:00 (about local time (LT) 11:00-15:00). A magnitude increases to more than 25 TECU during active conditions. During quieter conditions, the average TEC usually ranges from 15 to 20 TECU (Figure 14a).