Magnetometer for experimental study of earthquakes precursors

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Induction coil magnetometers (IM) are widely used for the experimental study of natural and man-made
magnetic fields variations in the frequency band from 10-4 till 106 Hz for science and engineering applications
in land and space conditions. They are probably the most widespread devices used for the magnetic field study.
Certainly, different application areas impose different requirements to the main IM parameters. For the study
of natural magnetic field variations of ionospheric and magnetospheric origin usually ultra low frequency (ULF)
band (0.001-3 Hz) is used. At present this frequency range gains in importance also at monitoring of lithospheric
magnetic activity in seismo-hazardous areas for application to short-time earthquake (EQ) forecasting. A big
number of publications confirm that ULF magnetic precursors were recorded from few weeks up to few hours
before EQ. IM sensors for ULF band usually have length 0.8-1.2 m, diameter 10-15 cm and weight few kilograms
with SND 0.1-200 pT/Hz0.5. Specially for EQ monitoring the IM set named LEMI-30 intended for the study of
magnetic field fluctuations in the frequency band 0.001 ... 30 Hz in land conditions was designed. It is ideal for
ULF signals monitoring and can be used both as a part of the computer measuring and registration equipment
and autonomously with any digital recorder. It has embedded communication unit (CAM unit), which connects
the sensors to PC and provides their power supply, satellite synchronization of data sampling and digitizing. All
three LEMI-30 sensors are similar within 0,1 dB. Their additional advantage is extremely high suppression of
50 (60) Hz mains noise what allows their using close to the living areas. The tests performed showed excellent
practically approved parameters and is widely used now in several countries. The peculiarities of the design of
induction magnetometer LEMI-30 and experimental results are discussed. This work is supported by STCU
contract № 4818.