Geophysical Journal | 2013 volume 35 3

Induction vector and horizontal tensor components variations before the Tohoku earthquake on the 11th March 2011 according to the data of Japanese geomagnetic observatories

© I.I. Rokityanskiy, V.I. Tregubenko, V.I. Babak, A.V. Tereshyn

This work is a continuation of a work [Babak et al, 2013] published in 1 of Geophysical Journal. The sources of variable magnetic field observed at the surface of the Earth are presented in the introductory part. The most reliable cases of lithospheric emission registered before strong earthquakes are described for five seismic regions of the World. The changes of electrical conductivity of the Earth's crust as a precursor of earthquakes are discussed. The review shows that geomagnetic response functions (induction vector and horizontal tensor) can be used as an earthquake precursor, which carry information both on lithospheric emission and changes in the electrical conductivity. Analysis of 18 Japanese geomagnetic observatories data (6 of them are away from the Tohoku earthquake epicenter less than 400 km) shows the presence of intense noise for periods less than 500 s. Application of noiseproof algorithms for calculation of response function components only partially reduced their influence. A large amount of processing was carried out and database of response functions for 10-20 years for 18 Japanese observatories was created. During the processing variety of record deficiencies were found, the cause of which is not always clear. Detailed processing of one-second data for 10 weeks before the Tohoku earthquake reveals anomalies of response functions temporal behavior: 7-9, 19-21, 33-36 and perhaps ~ 60 days before the event. Moments of amplitude and phase anomalies vary slightly for different periods of variations, for different components of the response functions, for different stations. This behavior is caused, on one hand, by the influence of geomagnetic activity and the contribution of noise, on the other hand, it can be the manifestation of precursors and co-seismic events, and this behavior may reflect a migration of lithospheric emission and/or changes in the electrical conductivity of the Earth's lithosphere. Decoding of this information can provide valuable information for understanding the physics of earthquake preparation and precursors formation.

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