# Co-Seismic Magnetic Field Perturbations Detected by Swarm Three-Satellite Constellation
## 3 Results of the Analysis
The vertical black line in the lower plot represents the point where the satellite crosses the earthquake latitude. The vertical green line is the candidate point where the earthquake-induced phenomena are supposed to start. In this case, we excluded the anomalies closer to the time of the earthquake occurrence (as in previous cases) and we selected the first anomaly after earthquake. Other anomalies are present in the track, while the selected one seems to be symmetric with respect to the epicenter. In the Supplementary Materials, more details and the other available Swarm magnetic data are represented (Figure S8). Figure 9: Residual of the Y component of Swarm Alpha magnetic field after the occurrence of the Mw 5.6 2017-01-16 earthquake. The vertical green line in the lower plot is the candidate point where the earthquake-induced phenomena are supposed to start. We excluded the anomalies at the beginning of the track, which are too close to the earthquake (this could be due to the equatorial electrojet or other equatorial electromagnetic phenomena). The selected point is the start of the wider anomalies in the track. We noticed that its duration is longer than other selected anomalies. The vertical black line represents the point where the satellite crosses the earthquake latitude. The Supplementary Materials show more details and the other available Swarm magnetic data are represented (Figure S7). Figure 11: Residual of the Y component of Swarm Bravo magnetic field after the occurrence of the Mw 6.4 2019-04-05 earthquake. The satellite passed above the epicenter some minutes before the earthquake occurrence; thus, no vertical black line is represented here (see previous figures where this line was plotted for more details). The vertical green line is the candidate point where the earthquake-induced phenomena are supposed to start. We selected this point, which is the start of a long “train” of anomalies in the track that persist for more than 9 min; other anomalies start after about 15 min, and thus cannot be generated by acoustic gravity waves. In the Supplementary Materials, more details and the other available Swarm magnetic data are represented (Figure S9). Figure 4:0 Residual of the Y component of Swarm Alpha magnetic field after the occurrence of the Mw 5.6 2019-04-07 earthquake. The vertical black line in the lower plot represents the point where the satellite crosses the earthquake latitude. The vertical green line is the candidate point where the earthquake-induced phenomena are supposed to start. We selected this point because it is the start of the only anomaly presented in the shown track. During the time of the occurrence of the earthquake, the satellite was below -70\({}^{\circ}\) geographical latitude, and thus, the data are cut. In the Supplementary Materials, more details and the other available Swarm magnetic data are represented (Figure S10). The acoustic gravity waves induced by seismic activities are only a type of a great variety of phenomena that could affect the ionosphere. For this reason, several disturbances affect these figures. Therefore, to measure the time of the arrival of the possible disturbance induced by the seismic event, a particular change in the waveform, concentrating in the part of the track that started after some minutes of the seismic event, was selected. We excluded the first minute of each track, because an acoustic gravity wave requires about 3.5 min to reach Swarm altitude (-450 km or more). The latitude of the satellite was also taken into account to understand if the disturbance could be due to the standard geomagnetic activity of the Earth's polar regions. We admit that this interpretation is not totally objective and unique, although sufficiently reasonable. For a quick comparison and validation, we also present in the Appendix A an automatic approach that is totally objective and practically confirms our results.