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Telecommunications and Radio Engineering
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Telecommunications and Radio Engineering

DOI: 10.1615/TelecomRadEng.v71.i18.70
pages 1707-1718

ULF MAGNETIC FIELD DEPRESSION AS A POSSIBLE PRECURSOR TO THE 2011/3.11JAPAN EARTHQUAKE

A. Yu. Schekotov
Schmidt Institute of Earth Physics, Russian Academy of Sciences, 10 B. Gruzinskaya St., Moscow, 123995, Russia
E. I. Fedorov
Institute of Physics of the Earth, Russian Academy of Sciences, 10, Bolshaya Gruzinskaya, 124995, Moscow, Russia
Y. Hobara
Research Station on Seismo Electromagnetics; UEC, Graduate School of Informatics and Engineering, Chofu Tokyo, Japan
Masashi Hayakawa
Hayakawa Institute of Seismo Electromagnetics Co. Ltd.(Hi-SEM), The University of Electro-Communications (UEC) Alliance Center #521, Advanced & Wireless and Communications Research Center, UEC, Chofu, Tokyo, 182-8585, Japan

ABSTRAKT

The depression (reduction in amplitude) of ULF magnetic field variations of magnetospheric origin is studied at various distances from the epicenter of the strongest earthquake (EQ) which occurred in Japan on March 11, 2011. For this purpose, we have used the ULF data in Japan observed by fluxgate magnetometers at three places located at distances of ∼ 300 km to ∼ 1300 km from the epicenter of the main shock. The period of data analysis is from December 1, 2010 to May 31, 2011. We have found a sharp increase in depression of the horizontal ULF magnetic field component at the frequency of 0.03 - 0.05 Hz (30-50 mHz) at all of three Japanese observatories (Kakioka, Memambetsu and Kanoya) three days before the first strong foreshock (Mω = 7.5) and five days before the main shock (Mω = 9). This peak in depression is found to be several times greater than all previous values, but the depression seems to be most enhanced at Kakioka, the station nearest to the EQ epicenter. So that it is likely that this phenomenon could be a possible precursor to the huge 3.11 EQ.