## 4 Case Analysis of Concepcion Earthquake
### Ionospheric Structure Anomaly before Earthquake  
The changes in the observed values of Nmf2 before the earthquake relative to the modeled values in the detection area (60\({}^{\circ}\)S-20\({}^{\circ}\)N, 90\({}^{\circ}\)W-50\({}^{\circ}\)W) were first explored. Due to the complex and dynamic interactions, the \(\delta\) value varied when time and region differed. After constructing GNM models, the statistics of \(\delta\) values from Nmf2 observations are necessary. As shown in Figure 5, the \(\delta\) values in the detection zone covering the Concepcion epicenter were extracted from 13 to 26 February. After data preprocessing of the COSMIC profiles, the filtered RO events were collected to compute the \(\delta\) values, and their two-fold average value (0.3433) was made as to the Nmf2 anomaly detection criterion. Here, the threshold results of \(\delta_{threshold}\) = 0.3433 were used as an ionosphere boundary limitation for systematic error and abnormal disturbance. If the \(\delta\) value was lower than the \(\delta_{threshold}\), the ionosphere was regarded as in the normal state; otherwise, it was considered to be affected by large energy fluctuations. It can be seen that, while most derivation was within bounds, Nmf2 anomalies could be detected at certain times, even those far exceeding the threshold. These responses indicated strong interactions with external factors. Four daily time phases (0-6 UT, 6-12 UT, 12-18 UT, and 18-24 UT) in this section are defined. Within the detection zone (60\({}^{\circ}\)S-20\({}^{\circ}\)N, 90\({}^{\circ}\)W-50\({}^{\circ}\)W), the daily latitude-time variations impending the earthquake for determining anomalous Nmf2 are analyzed(see Figure 6). The \(\delta\) value of Nmf2 disturbance detected at most observation points is less than 0.2, while excess outliers appear in three phases: 6-18 h on February 15, 12-18 h on February 21, and 6-12 h on February 25. To separate the influence of internal/external factors from the seismo-ionosphere effects, the uniqueness of regional enhancement near the epicenter needs to be further explained. Responding to RO Nmf2 \(\delta\) > 0.3433, all the disturbing events within 15 days prior to the shock were extracted. Three episodes were delineated: the magnetic-influence episode (February 15), the local effect episode (February 21 and 25), and the other quiet episodes. Based on the spatial distribution in RO in Figure 7, strongly disturbing events and local effects were studied in each episode. Figure 5: The \(\delta\) statistics in detection zone (60\({}^{\circ}\)S-2\({}^{\circ}\)N, 90\({}^{\circ}\)W-50\({}^{\circ}\)W) from 13 to 26 February. Figure 6: Disturbance of Nmf2 (60°S–20°N, 90°W–50°W) near the epicenter of Concepcion earthquake in the near earthquake stage (2010.2.13–26). The arrow in the figure shows the period of obvious anomaly. Figure 7: The spatial distribution statistic of abnormal Nmf2 RO events in different episodes, where the focal sphere represents the epicenter. Figure 7A shows the global ionospheric disturbances on February 15. The results show that a wide range of ionospheric anomalies occurred worldwide. With the active geomagnetic activity and occurrence well before the shock (12 days prior to the shock), the geomagnetic activity is the main factor of the Nmrf2 anomalies. By contrast, in Figure 7B, with the sporadic points outside the seismogenic area, there was a noticeable disturbance in the F2 layer near the epicenter on February 21 and February 25. A pronounced local effect on both days is clearly visible. Lastly, the F2 layer reaction in the quiet episode was inspected (see Figure 7C). There was a significant ionosphere variation in the South American sector and North America high latitude within the 15 days before the shock. In the Atlantic sector (near 0\({}^{\circ}\)E), the disturbed Nmrf2 could be captured as well. These Nmrf2 anomalies have a rather similar spatial distribution of ionosphere scintillation [38].