## 5 Conclusions  
In this paper, we extended the work published by [PERSON] et al. (2019) to a longer period (8 years) than that originally analyzed (4.7 years) of _Swarm_ data correlated with M5.5+ shallow earthquakes. Here, we not only provide an analysis extended to the first 8 years of _Swarm_ data but also introduce some new methodologies to improve the definition of the anomalies (by frequency analysis) and in terms of better investigation of the results--in particular, searching for possible influences of the seismo-tectonic context on the possible pre-earthquake electromagnetic signals. New methodologies and investigations are proposed to take into account the frequency of the signal and the different anticipation times of anomalies expected for several magnitude earthquakes. We found that several concentrations of ionospheric anomalies are statistically significant, well overpassing the given thresholds of \(d\geq 1.5\) and \(n\geq 4.0\)--i.e., they are very much greater than the concentrations obtained from the space-time-homogenously-distributed anomalies, and we can infer that the earthquakes associated with such significant concentrations could be more likely \"predicted\", even if this is not the goal of the present work. By the ROC curve, we confirm that the anomalies selected by WSC and the aforementioned statistical criteria over \"\(d\)\" and \"\(n\)\" have predicting capabilities, showing an AUC that is 1.67 times better than that of a random predictor. Future studies could be oriented to filter the signals that are most prone to earthquake-induced anomalies (for example, [PERSON] et al. (2019)) in order to better depict the signal \"features\" of possible seismo-induced phenomena in the ionosphere. Nevertheless, although such ionospheric pre-earthquake disturbances are still widely debated, there is some evidence, in the literature and in this paper, that they statistically exist. Our main conclusions are:  
1. The anticipation time \"\(\Delta T\)\" of the anomaly increases with the magnitude of the incoming earthquakes following the Rikitake laws ([PERSON], 2016), with these specific coefficients being \(\Delta T_{mag}=10^{-0.96+0.51\cdot M}\) and \(\Delta T_{Ne}=10^{-3.46+0.83\cdot M}\) for the magnetic field \"mag\" and electron density data, respectively. The anticipation time of large earthquakes (M7.5+) seems to be some years before the event and has been detected. 2. The focal mechanism seems to have a small or null influence on the generated frequency of the possible pre-earthquake anomalies. 3. Earthquakes localized in the land areas tend to be preceded by lower frequency anomalous signals, while sea earthquakes are more likely to be preceded by faster signal anomalies. 4. The _Swarm_ magnetic field signal anomalies generally show a better correlation with earthquakes than the electron density ones do. 5. A more selective set of parameters, achieved here by the investigation of the signal frequency, reduces the size of the anomaly dataset, and it is shown that the possible correlation with the seismic event has a higher statistical significance for both the magnetic field and _Ne_ observations. 6. Frequency analysis seems to be fundamental in some cases: for electron density, we find a higher correlation with anomalies, with a signal period in the range of 25-50 s.