Shinshu University
It has been documented over hundreds of years that various electromagnetic anomalies occur during a few weeks before the occurrence of a large earthquake. These electromagnetic anomalies are variations that appear in telluric current, geomagnetism, electromagnetic waves etc. before the earthquake.
Although there are various models to explain the mechanism, the large current generated at the source was not fully explained. For example, many researchers thought that the stress applied to the fault produced an electric current, but the stress applied to the fault takes place over hundreds or thousands of years before the occurrence of the earthquake. It is a common belief among seismologists that it is impossible for the stress to suddenly increase and generate a large current just before the earthquake, and therefore the mechanism had not yet been explained.