Role of ULF emissions in the terrestrial electromagnetic environment

结果表明，电磁现象正成为地震短期预报的一个很有前途的候选者。在不同频率范围（从DC到HF）的地震射电辐射中，最有希望的是ULF辐射，尽管它的历史并不充分。在这项研究中，我们希望尽可能多地积累有关地震超低频发射的令人信服的数据，然后利用这些数据来阐明它们的产生和传播机制。(1)俄罗斯ULF传感器（扭转型磁力仪）在伊豆（和千叶）地区工作得很好;特别是，它们的灵敏度足够好，并且正在定期积累数据。(2)伊豆中的差分阵列（由3或4个传感器组成）对于地震-ULF发射非常有效，使得它将地震-ULF波的S/N比提高了30- 40 dB。(3)极化比（Z/H Z垂直和H水平分量的超低频磁场）再次被证实是有效的区分地震超低频发射从其他噪音（地磁脉动）。(4)其他地震的超低频数据（比亚克、关岛等）分析了我们非常重视分形分析。结果表明，这种分形分析有助于研究震源区的大尺度特征。

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.