# Co-Seismic Magnetic Field Perturbations Detected by Swarm Three-Satellite Constellation
## 3 Results of the Analysis
A zoom around the selected anomalies is provided, where it is visible that the anomaly has been preceded by a few different samples circled in red, which suggests this point as the possible arrival of a co-seismic signal at the satellite position. In the Supplementary Materials, more details and the other available Swarm magnetic data are represented (Figure S1). Figure 5: Residual of the Y component of the Swarm Alpha magnetic field after the occurrence of the Mw 5.8 2014-10-22 earthquake. The vertical green line is the candidate point where the earthquake-induced phenomena are supposed to start. We selected this anomaly because it is the first after the earthquake occurred, while those occurred after 7 min are localized at high latitudes, and thus more likely due to magnetic auroral activity. The data after +70\({}^{\circ}\) of geographical latitude are cut. The satellite passed just before the earthquake over the latitude of the epicentre. After little more than 10 min, the satellite overpassed the 70\({}^{\circ}\) north geographical latitude, and thus, the data are not shown. In the Supplementary Materials, more details and other available Swarm magnetic data are represented (Figure S2). Figure 6: Residual of the Y component of the Swarm Alpha magnetic field after the occurrence of the Mw 6.9 2015-11-11 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 anomaly because it is the first on the track after the earthquake. Moreover, we noticed that its shape is different from the other anomalies, as the amplitude is almost constant (peak-to-peak about 1 nT) during its duration (little more than 1 min), which is different from the other anomalies that increase, reach a maximum and then decrease. In the Supplementary Materials, more details and the other available Swarm magnetic data are represented (Figure S3). Figure 8: Residual of the Y component of Swarm Bravo magnetic field after the occurrence of the Mw 5.7 2016-06-15 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; a zoom of the signal around this point is provided because the high-latitude disturbances increased the vertical scale. We selected this point because the signal after this point presents a behavior similar to the one of Figure 6 but with lower amplitude. The anomalies after 14 min are probably due to the south auroral magnetic activity. About 18 min after the earthquake, the satellite went below \(-70^{\circ}\) geographical latitude, thus, the data are not shown. In the Supplementary Materials, more details and the other available Swarm magnetic data are represented (Figure S6). Figure 7: Residual of the Y component of Swarm Charlie magnetic field after the occurrence of the Mw 5.7 2016-04-17 earthquake. The vertical black line (at the right of the lower graph, about 20 m after the earthquake) 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. Additionally, a zoom of the track around the selected point is provided. In the selection, we take into account that the disturbance between 0 and 1 min appears too early to be an acoustic gravity wave with respect to the earthquake origin time, while the selected one is more reliable. The disturbance between 1 and 6 min seems to be characteristic of this orbit. In the Supplementary Materials, more details and the other available Swarm magnetic data are represented (Figure S4). Figure 10: Residual of the Y component of Swarm Charlie magnetic field after the occurrence of the Mw 6.0 2018-07-17 earthquake.