# Applied Engineering Using Schumann Resonance for Earthquakes Monitoring
## Materials and Methods  
### Seismic Phenomena and ELF Waves  
The importance of the study of precursors or indicators of seismic activity is a key to early detecting and preventing succession of major disasters [37]. Seismic events can be related to different types of events. There is evidence indicating that a link between the lithosphere-atmosphere-ionosphere occurs before the occurrence of seismic events [38]. Understanding these processes' physics and possibility of it being used to develop an early detection system is the subject of great research and development in recent decades. It has demonstrated the influence of seismic events on this type of ELF signals, setting both types of signals artificially and analyzing the behavior of electromagnetic waves when they are motivated by earthquakes [32]. One of the first attempts to standardize ELF wave monitoring on a global scale dates back to 1985, thus it is considered a fairly developed work topic in recent years [39]. Also, there exist other publications that detect anomalies in signals produced by the seismic phenomenon. One example is the correlation between the seismic phenomena and the Outgoing Long-wave Radiation (OLR) data. These signals can be observed by satellites [16], such as the case of the Chinese Earthquake (Wenchuan and Lushan earthquakes) that occurred between 2006 and 2013. The detection of such anomalies can also be carried out by observatories or ELF/VLF stations [33]. These observatories are located in very low-noise locations. In them, the ELF/VLF range (signals up to 300 Hz) and the orthogonal components of the magnetic field (B\({}_{\mathrm{x}}\), B\({}_{\mathrm{y}}\) and B\({}_{\mathrm{z}}\)) can be measured. Three orthogonal induction coil magnetometers are normally employed. The B\({}_{\mathrm{x}}\) component usually represents the North-South (NS) geomagnetic component of the magnetic field. It can be determined by the induction magnetometer whose axis is aligned with the direction NS, so that the component B\({}_{\mathrm{x}}\) is sensitive to waves propagating in the East-West (EW) direction. The other component of interest is the B\({}_{\mathrm{y}}\) component that is sensitive to waves propagating in the meridian plane [40]. ELF/VLF signals propagate through the environment, and are detected by an appropriately located ELF/VLF receiver over a zone where enhanced radio emissions are happening prior to a great earthquake. Some studies about ionosphere-atmosphere-groundwater phenomena great earthquakes (M > 6.5) associate this occurrence with strong ELF noises or anomalies present in signals located in the ELF frequency band [41]. One of the most important ELF signals, which are affected by the presence of these seismic events is the Schumann Resonance (SR) [42]. These resonances are produced by natural phenomena; they were predicted theoretically in the 50's, but no graphical representation of them was established until 1962 [43]. The SR signals are very weak signals, on the order of PicoTesla, and occur in the space between the earth and the ionosphere, as indicated in Figure 1. This space acts as a resonant cavity or waveguide for these signals, since it has a finite or limited size [44]. The measurement of these signals allows developing various applications. This includes determining the global lightning activity or storms by diurnal variations in the amplitude of the signal continuous records [45], or the study of planetary electromagnetic environment [46]. Another application of SR signals that has aroused great interest in recent years is as a global tropical thermometer. Since a frequency shift of resonance peaks has been observed related to the global temperature increase of the planet or global warming [47]. In regards to the relationship between the mean of these phenomena ELF and the existence of seismic events, there are relatively recent works showing the appearance of abnormal variations in the amplitude and phase of these ELF signals when crossing regions of certain seismic activity.