## 3 Results
### Swarm Magnetic Field Results
Only the significant part of the superposed space-time graph is represented. The statistical indications of \(d\) (how many times the maximum real concentration is higher with respect to the random one) and \(n\) (how many standard deviations there are in which the real largest concentration is greater than the random one) are also shown. Such maximum concentrations (as objectively identified by the WSC algorithm) have been highlighted by a red or orange circle (the last one for a less significant concentration in terms of the Rikitake law). The color bar represents the density of the anomalies in terms of the number of anomalies per square degree. with the period of the signal, this being the time between the maximum concentration of the anomalies and the occurrence of the earthquake. This observation could be crucial for a future system to predict earthquakes, as the frequency of the signal could give important information of the time-lapse to the earthquake. We tried to provide a rough linear fit (see Figure S5 in the Supplementary Materials) of such an anticipation time, obtaining:  
\[\Delta T=-24\ (\pm 19)+4.01\ (\pm 0.82)\cdot P \tag{4}\]  
where \"\(\Delta T^{\prime}\)\" is the anticipation time in days, and \"\(P^{\prime}\)\" is the period of the signal in seconds. The fit provides a positive slope of about 4.0 days/s. The fact that the fit provides a negative intercept and then a possible negative anticipation time (and thus an effect after the earthquake) could be explained by the fact that the period stops at about 6 s before the earthquake's occurrence (i.e., \(\Delta T=0\), then \(P=6\) s). We provide a specific discussion on these results in Section 4.4. We finally noted that there seems to be a very long period underlined by dashed green boxes in Figure 3, with higher anomaly concentrations with respect to the rest (the identification of the green boxes is taken by sight considering the \"more red or brown\" bins, subjectively). We speculate that the density of the anomaly in the tails (i.e., before or after the green dashed box) is not due to the earthquake and that it is in the background due to other sources, while the increase in the anomalies could be related to a sort of seismic activation and to the consequences of the seismic event after their occurrence. Even these higher anomaly regions increase their duration (before the earthquake) with the period of the investigated signal. Future studies are fundamental to investigate this aspect better. Table S1 (in the Supplementary Materials) summarizes the main statistical results for all the investigated combinations of the 8-year _Swarm_ magnetic field data correlated with M5.5+ shallow earthquakes. In particular, the two statistical quantities \(d\) and \(n\) are reported, along with the indication of when the maximum concentration of anomalies  
Figure 3: 8-year _Swarm_ Y-mag data separated for frequency content in the anomalies correlated with M5.5+ earthquakes from 500 days before until 500 after their occurrence. The color bar represents the density of the anomalies in terms of the number of anomalies per square degree. The anomalies have been selected with higher signal content in three different period bands: (**A**) from 2 s to 10 s, (**B**) from 10 s to 25 s and (**C**) from 25 s to 50 s.  
occurs in the bin closest to the epicenter (negative if it occurs before the earthquake and positive if it happens after) and how many earthquakes are associated with anomalies in the pixel with the maximum concentration of anomalies. When a concentration passed the statistical evaluation criteria defined in [29] (i.e., \(d\geq 1.5\) and \(n\geq 4.0\)) and occurred before the earthquake, we underline the row in green.