# Successful Tests on Detecting Pre-Earthquake Magnetic Field Signals from Space
## 2 Materials and Methods  
### Swarm Satellite Observations Data  
In this study, to investigate magnetic field anomalies possibly caused by earthquakes that happened in the Alpine-Himalayan belt, we used Swarm satellite data. Swarm is a three-satellite mission of the European Space Agency that was launched and placed into a quasi-polar orbit in late 2013 to study the Earth's magnetic field [30]. Two of the satellites, namely Alpha (SW-A) and Charlie (SW-C), fly side by side in a low orbit with an altitude of nearly 450 km, while the third satellite, Bravo (SW-B), is in a higher orbit of about 510 km. This particular orbital configuration was chosen to achieve various scientific aims: for example, the lateral flight of two satellites, Alpha and Charlie, can lead to the measurement of aligned field currents flowing in the radial direction [31]. The Alpha and Charlie satellites fly close together, and the east-west separation of the orbits of these two satellites is approximately 1.4 degrees, and their inclination angle in polar orbits reaches 87.4 degrees. Also, their height is a significant parameter because it was chosen to develop  
Figure 1: Earthquakes used in this study. Epicenters of earthquakes with a magnitude (“mag” in the legend inside the figure) greater than or equal to 5.0 that occurred in the Alpine–Himalayan belt (\(20^{\circ}\leq\text{lat}\leq 60^{\circ}\) and \(-20^{\circ}\leq\text{long}\leq 100^{\circ}\)) from 2014 to 2023 (source: [[https://www.usgs.gov](https://www.usgs.gov)]([https://www.usgs.gov](https://www.usgs.gov)); accessed on 1 February 2024). the mission as long as possible. In this way, it will be feasible to monitor the geomagnetic field for a complete solar cycle (11 years), which is very important because solar activity has one of the most significant effects on the geomagnetic field. The three satellites are identical, so each satellite is equipped with the same advanced magnetometers providing high-precision and high-resolution measurements of directional strength and magnetic field variation, supplemented by electric field and plasma parameters measurements, accelerometers, and accurate orientation. These observations are presented as level 1-b data, which are calibrated and formatted in time series. The research targets assigned to this mission are as follows: (1) studies of core dynamics, geodynamic processes, and mantle-core interaction; (2) mapping the polarization of the lithosphere and its geological interpretation; (3) determining the 3D electrical conductivity of the mantle; and (4) investigating the electric currents that flow in the magnetosphere and ionosphere. However, a challenging part is to separate the different sources in the core, lithosphere, ionosphere, magnetosphere, etc., to obtain the total measured magnetic field [32]. Some of the principal results obtained so far by the Swarm satellite mission are as follows: a map of the magnetic field of the lithosphere with a high resolution of 250 km [33], and the effect of ocean tides on the geomagnetic field and electromagnetic induction produced by ocean circulation [34; 35]. In this study, we use magnetic field vector components and total intensity with a low rate of 1 s sampling and level 1-b to analyze the magnetic field as observed by the lower orbit satellites, i.e., SW-A and SW-C. [PERSON] et al. [36] performed a worldwide systematic correlation analysis using about 5 years of magnetic field Swarm satellite data and earthquakes. One of their main results was to confirm the [PERSON] law [37], which states the anticipation time of the appearance of the earlier precursors from satellite depends on the earthquake magnitude: the larger the magnitude, the longer the anticipation time of the earlier precursor. This time represents the beginning of the appearance of the studied precursor, which then will continue to appear sporadically up to the approaching of the earthquake.