SEISMOMAGNETIC SIGNALS AS EARTHQUAKES PRECURSORS

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The earthquakes monitoring in all world reveals that the “seismomagnetic” fluctuations 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 measurement technology of these signals has several
peculiarities. The lithospheric ULF EQ magnetic precursors as a rule are very weak and their frequency range
is overlapping with signals of ionospheric origin. The method of their selection at more powerful magnetic
variations of other nature background is proposed. For demonstration of newly proposed selection method
efficiency, the experimental data from some seismo-hazardous regions are processed and positive results are
presented. Then the magnetometers with search-coil (SC) and fluxgate (FG) sensors and minimum possible
spectral noise density (SND) level used for the study of ULF magnetic precursors are compared. SC sensors for
ULF band usually have length 0.8-1.2 m, diameter 10-15 cm and weight few kilograms. These factors increase
real SC SND because of induction effect in the Earth’s magnetic field. To overcome majority of these problems,
a specialized FG with sensor length 10 cm has been developed which has SND in ULF band (0.001-0.03 Hz)
about 3-30 pT/Hz0.5. This is considerably less than SND for the best recent SCs. The details are discussed in
the report. This work is supported by STCU grant 4818.