Electromagnetic earthquake precursory signatures in the ULF RANGE: perspectives of the studies

Interest in research on the detection of earthquake (EQ) precursors is growing year by year. In this direction, the paper analysed the results of earlier studies, as well as positive results of some studies conducted in the last 5 years. In particular, during the study of EQs, ultra-low frequency (ULF) precursors attract special attention. The study compared the results of electromagnetic (EM) monitoring studies conducted in the ULF range in earlier years and the results of EM monitoring studies conducted in the last 5 years have been compared.

Emergence of earthquakes footprint in natural electromagnetic field variations

Purpose. It is well-known that strong earthquakes are typically accompanied by some phenomena which relate to variations of natural electromagnetic fields. Based on the idea about the mechanism of lithosphere–atmosphere–ionosphere coupling we expect to detect some precursors of strong natural earthquakes in electromagnetic data sets recorded by magnetotelluric instruments far enough from epicenters.

Seismogenic ULF variations of the magnetic field

The earthquakes monitoring in all world reveals that the “seismogenic” fluctuations of magnetic field in wide frequency band often occur before these seismic events. We believe that the most reliable information is concentrated in ultra low frequency (ULF) band (0.001-3 Hz). The earthquake ULF magnetic precursors of lithospheric origin are very weak as a rule and their frequency range is overlapping with signals of ionospheric origin. The new method of the seismomagnetic signals selection at the background of more powerful magnetic variations of other nature is proposed.