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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Oral Presentation 2035
Towards extraction of precursory changes from noisy electromagnetic data
Prof. Toshiyasu Nagao
Earthquake Prediction Research Center Tokai University IASPEI
Takayuki Kawakami, Keizo Sayanagi, Jun Izutsu, Makoto Harada, Makoto
Uyeshima, Tada-Nori Goto
There are a number of reports that electromagnetic data contain precursory changes related to
earthquakes and volcanic eruptions. However, artificial noises, such as leakage current from DC-driven
trains and electromagnetic noises from factories, are extremely large in Japan over wide frequency
ranges. Therefore, it is very difficult to extract precursory conductivity changes and telluric current
changes due to electrokinetic effects by using the conventional techniques (magneto-telluric method,
apparent resistivity monitoring, and spontaneous potential monitoring, etc.).During the last decade,
some researchers have been claiming that well-considered information processing techniques (principal
components analysis; PCA, independent components analysis; ICA, fractal/multi-fractal analyses, and so
on) are tools quite useful to extract precursory changes. Their approaches sometimes seemed working
well. However, most of the cases, they only demonstrated that some abnormal changes were observed
before impending earthquakes and volcanic eruptions. The abnormal changes, however, could have
been due to other causes. In order to improve the situation, it is considered that we should pay more
attention to remove the theoretically explainable changes (magnetic pulsations and their induction
components, tidal components due to earth and ocean, etc.) at first by using the well-designed remote
reference techniques (e.g., inter-station transfer function technique using wavelet transformation).
Then, we apply the information processing techniques to extract precursory changes and consider their
theoretical backgrounds. Analyzed data in this study is telluric current data since 1996 at Ito Station,
east coast of Izu Peninsula and ocean bottom electro-magnetic data off Izu Peninsula since 2005. In the
region, during the study period, we had three severe seismic swarms in 1996, 1998 and 2006. Izu
Peninsula, being close to Metropolitan Tokyo, is a region of very high artificial noise. If we succeed in
extracting meaningful precursory changes in this region, we believe that it is an enormous progress in
seismo-electromagnetics.
Keywords: precursor, earthquake prediction, electromagnetics