Observations of ULF/ELF anomalies detected by DEMETER satellite prior to earthquakes
Résumé
Seismo-electromagnetic effects refer to the electric and magnetic field perturbations found during the course of earthquakes. Furthermore, in the range of electromagnetic emissions, stress is laid on the ultra low frequency (ULF) and extremely low frequency (ELF), due to their reasonably higher penetration depth as compared to the other higher frequencies. The emissions are observed prior to moderate and strong earthquakes. One of the most promising diagnostic tools for studying the electromagnetic anomalies is using satellite based technique. Some important electric field variations observed prior to two individual earthquakes are discussed in this paper, one in Arunachal Pradesh, India (28.87°N, 94.60°E, 20:06:42 hrs UTC) measuring 5.9 and the other in the west coast of Columbia (6.86°N, 77.8°W, 20:50:46 hrs UTC) measuring a stronger 6.2 on the Richter scale. The anomalies are reported to occur in the ULF/ELF range. The observations have been detected prior to both the events using the low altitude satellite DEMETER (height ≈710 km), which is aimed at studying the ionospheric perturbations related to earthquakes and volcanic eruptions.