## 4 Discussion
### General Comparison of the Number of \"Pre-\" and \"Post-\" Earthquake Anomalies  
Finally, we provide an objective comparison of the number of anomalies detected before and after the earthquake with a symmetrical analyzed time in Table 4. In this \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Focal Mechanism**} & **Earthquakes with Anomalies in the Band 2-10 s** & **Earthquakes with Anomalies in the Band 10-25 s** & **Earthquakes with Anomalies in the Band 25-50 s** & **All the Earthquakes** \\ \hline strike-slip & **50 (35.2\%)\(-\)10.1\%** & 54 (39.4\%)\(+0.6\%\) & **54 (37.2\%)\(-\)5.0\%** & 846 (39.2\%) \\ \hline reverse & **67 (47.2\%)\(+\)10.5\%** & **62 (45.3\%)\(+\)6.0\%** & 64 (44.1\%)\(+3.4\%\) & 922 (42.7\%) \\ \hline normal & 25 (17.6\%)\(-\)2.8\% & **21 (15.3\%)\(-\)15.4\%** & 27 (18.6\%)\(+\)2.8\% & 391 (18.1\%) \\ \hline
**Sea or land** & & & & \\ \hline Land & **16 (11.0\%)\(-\)35.2\%** & 24 (17.5\%)\(+3.6\%\) & **30 (20.6\%)\(+\)21.5\%** & 372 (16.9\%) \\ \hline Sea & **130 (89.0\%)\(+\)7.2\%** & 113 (82.5\%)\(-\)0.7\% & 116 (79.5\%)\(-\)4.4\% & 1827 (83.1\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Investigation of a possible relation with the focal mechanism with the recorded frequency of the magnetic field anomalous signals from the _Suarm_ and sea or land epicenter location. The significant percentage of deviation from the standard earthquake distribution (i.e., the ones \(\geq 5\%\) in their absolute value) are marked by bold numbers. Green (red) numbers represent positive (negative) deviation percentages with respect to the reference. table, we provide the difference between the anomalies detected before and the ones detected after the earthquake. The percentage of such difference refers to the anomalies after the earthquake, and the uncertainty is estimated as the square root of the maximum number of anomalies. We consider the result significant if the difference is greater than the estimated uncertainty. A negative difference indicates that the number of anomalies detected after the earthquake is greater than the number of those detected before the earthquake. Normalization with respect to the total hours of geomagnetic quiet time is provided to take into account the possible imbalance in the investigated events due to our cut of the geomagnetic perturbed times (i.e., the ones when 1 Dst \(\mid\) \(>\) 20 nT and/or ap \(>\) 10 nT). The normalized quantities are provided in the second line of each cell with the label \"Norm\". Such imbalance due to geomagnetic activity can be due not only to sporadically geomagnetic storms but also to the different solar activity that was at a \"minimum\" at the beginning of the _Swarm_ mission and is now in the increasing stage toward the next \"maximum\". The incomplete dataset in the first and last 500 days of analysis could enhance such a difference in the solar cycle. Most of the investigations have a significant differential number of anomalies that preceded the earthquake, supporting the hypothesis that some of these anomalies are induced by the preparation phase of earthquakes. The analysis with the higher percentage of pre-earthquake anomalies is the Y-East magnetic field in the period band of 2-10 s. Concerning the _Swarm Ne_ anomalies in the period band of 25-50 s, we note a relatively high percentage considering the high number of total anomalies (40,219) compared with the result of the \"Y, no-band\". Furthermore, if we look at the general pattern, it is possible to suppose that the pre-seismic anomalies start about 400 days before the earthquake as the color of the concentration becomes darker (about orange, i.e., with a concentration of anomalies equal to or greater than seven anomalies/degree\({}^{2}\)) until the earthquake and persists until about 250 days after the earthquake, when it seems to go back at a background level (which shows a yellow color corresponding to about 5.5 anomalies/degree\({}^{2}\)).