# Successful Tests on Detecting Pre-Earthquake Magnetic Field Signals from Space
## 3 Results and Discussion  
In this research, all Swarm satellite level 1-b data of the magnetic field components with a sampling rate of 1 Hz obtained from Alpha (SW-A) and Charlie (SW-C) satellites from the 10 days preceding Mw5.0+ earthquakes occurring from 2014 to 2023 in the Alpine-Himalayan seismic belt have been investigated. We restrict the investigation to just 10 days before earthquakes because we want to focus on the last short-term phase of the earthquake preparation, although we recognize that precursors can appear much earlier [36; 37; 47]. After applying the automatic algorithm of detection to the database among all the earthquakes (1077 earthquakes), magnetic anomalies were identified in 900 events. Table 1 shows the number of earthquakes present in different magnitude ranges, and from this number, how many earthquakes have at least one orbit containing magnetic anomalies. The statistics presented in Table 1 are for the general case and do not take into account the status of geomagnetic indices. When we consider only satellite data detected during the quiet state of the ionosphere, so excluding those orbits with high geomagnetic indices, the number of examined earthquakes reduces to 786 (Table 2). Out of this total, 615 earthquakes have at least one orbit with magnetic anomalies. Earthquakes that have not shown any magnetic precursor signals mostly have lower magnitudes, i.e., between 5 and 5.5. Indeed, this could be due to the lower energy associated with this type of earthquake and the sensitivity of the sensors on the satellites. According to the obtained results, it can be said that most anomalies are observed in the Y component of the magnetic field [36; 48]. In a few cases, anomalies have also been observed in the X and Z components of the magnetic field, which frequently occurred in faults with oblique and reverse mechanisms. Of course, this issue needs further investigation, which is outside the scope of the present study. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Magnitude Range**} & **Number of EQs That** & \multirow{2}{*}{**Total Number of EQs**} & \multirow{2}{*}{**Percentage (\%)**} \\  & **Exhibit Anomalies** & & \\ \hline Full range & 900 & 1077 & 83.5 \\ \hline
5.0–5.5 & 663 & 821 & 80.8 \\ \hline
5.5–6.0 & 155 & 172 & 90 \\ \hline
6.0–6.5 & 53 & 55 & 96 \\ \hline
6.5–7.8 & 29 & 29 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Number of earthquakes regardless of geomagnetic conditions. The ratio of the number of earthquakes that had magnetic anomalies to the total number of earthquakes is calculated for different magnitude ranges and for the entire magnitude range of earthquakes. From previous research [14; 36], we know that the Y component of the magnetic field is usually the least affected by anomalies due to sources outside the lithosphere, such as magnetic storms, and most changes in this component are caused by factors inside the lithosphere. On the other hand, X and Z components are more affected by the anomalies outside the lithosphere [48]. For this reason, more attention has been paid to quiet geomagnetic conditions in the use of X and Z components, and in one case, there is a geomagnetic perturbation, so the anomalies of the X and Z components were not used. Analogous anomalies have been seen in research by other authors. For example, [PERSON] et al. [16] were able to investigate 12 major earthquakes in a period from 2014 to 2016, and observed a series of anomalies in the magnetic field for each of them. Afterward, using the shift in the cumulative number of anomalies, they attempted to show a variation in the magnetic field before some significant events. However, in the present research, new and more extensive results have been obtained from the analysis of the satellite magnetic field anomalies.