# Geophysical Coupling Before Three Earthquake Doublets Around the Arabian Plate
## 3 Results
### Ionosphere  
In order to investigate the ionosphere, firstly, all the available tracks of the Swarm satellites that crossed [PERSON]'s areas of the three cases have been automatically processed using the code MAgnetic Swarm anomaly detection by Spline analysis (MASS) algorithm [83]. It compared the residual root mean square (rms) in a moving window of 3-degree latitude with the Root Mean Square (RMS) evaluated on the whole track within 50\({}^{\circ}\) geomagnetic latitude. If the rms \(>\) kt \(\times\) RMS and geomagnetic conditions were quiet, the windows are defined as anomalous. \"kt\" is a threshold to define the anomalies and, in this work, has been set equal to 2.5. The selected tracks have been processed using the method described previously in the Data and Methods section. These methods have been applied to the three orthogonal components of the geomagnetic field, X-North, Y-East, and Z-Centre, and then, the residuals are analysed and visualised. In the manuscript, we report an example for each case study in Figures 7-9, and all the other tracks are provided in Supplementary Materials. In particular, Figure 7 shows an interesting track that preceded about 56 days (i.e., roughly two months) of the earthquake doublet of Dehloran (Iran) 2014. The track was acquired by Swarm Charlie on 22 June 2014 at 16:37 UT. The geomagnetic conditions were quiet; in fact, Dst = \(-\)8 nT and ap = 3 nT. Also, the Auroral Electrojet (AE) index was quiet for the whole day. The solar wind speed was about 360 km/s, which is a low value below a threshold of 400 km/s, sometimes used to define a higher speed of solar activity (even if there is a change in the function of the solar cycle). The solar flux measured at the wavelength of 10.7 cm was 89 SFU at this time, which also suggested a low solar activity. In addition, we reported in Appendix A the complete plot of solar activity (wind speed and flux) during the whole analysed time for the three case studies. It's evident that an anomalous signal at 28\({}^{\circ}\) N of geomagnetic latitude with an intensity of about 2 nT peak-to-peak is at the same latitude as the future epicentres. Considering that the signal was fully inside [PERSON]'s area and acquired in very quiet geomagnetic conditions, we consider it a good candidate for pre-earthquake electromagnetic disturbance. This is similar to the ones identified before the Italian seismic sequence 2016-2017 but with a much higher anticipation time [84]. Figure 6: Time series of sulphur dioxide six months before Bandar-e Lengeh (Iran), Iran, 2022 earthquake doublet. The meaning of the lines and colour is the same as in Figure 3. The following years have been automatically excluded from the statistics for outliers: 1991, 2001. Figure 7: Residual of Swarm Alpha (**above**) and Charlie (**below**) magnetic data acquired on 22 June 2014 at 16:37 UT. The green circle represents [PERSON]’s area of the Dehloran (Iran) 2014 earthquake doublet. The red vertical line is the projection of the satellite orbit on the map. The mean epicentre is shown as a green asterisk. The red dashed ellipse marks the anomaly potentially associated with the earthquake. Figure 8 shows one of the three anomalous days detected by Swarm Alpha and Charlie in the six months before Kilmia, Yemen, 2018, which are 5, 8 February and 15 June 2018. We selected to report in the manuscript the one recorded by Swarm Alpha on 5 February 2018 as it's the one with more reliable characteristics to be considered as a pre-earthquake-induced signal. In fact, the one acquired on 8 February 2018 shows little other disturbances at several latitudes, suggesting its source could be more a global ionospheric perturbation instead of a local phenomenon, like the one we are searching for. On the other hand,  
Figure 8: Residual of Swarm Alpha (**above**) and Charlie (**below**) magnetic data acquired on 5 February 2018 at 17:15 UT. The green circle represents [PERSON]’s area of the Kilmia, Yemen, 2018 earthquake doublet.