Role of ULF emissions in the terrestrial electromagnetic environment

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Result activities have shown that the electromagnetic phenomena are becoming a very promising candidate for the short-term earthquake prediction. Among the seismo-radio emissions in a different frequency range (from DC to HF), the most promising is the ULF emission, though its history is not sufficient. In this research, we would like to accumulate the convincing data on seismo ULF emissions as many as possible, and then by using those data we will elucidate the mechanism of their generation and propagation.This research has indicated the following important findings as listed below.(1) Russian ULF sensors (torsion-type magnetometer) works very well in IZU (and Chiba) area ; especially, their sensitivity is good enough, and the data are being accumulated regularly.(2) Differential array in IZU (composed of 3 or 4 sensors) is very effective for seismo-ULF emissions, such that it increases the S/N ratio for seismo-ULF waves by 30-40dB.(3) The polarization ratio (Z/H Z vertical and H horizontal component of ULF magnetic field) is again confirmed to be effective in distinguishing seismo-ULF emission from other noises (geomagnetic pulsations).(4) ULF data for other earthquakes (Biak, Guam etc.) were analyzed. and we paid great attention to the fractal analysis. It is found that this kind of fractal analysis would be useful to investigate the large-scale characteristics of the focal zone.