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ultra low frequency
Ultra low frequency (ULF) is the ITU designation〔(【引用サイトリンク】url=http://www.itu.int/dms_pubrec/itu-r/rec/v/R-REC-V.431-7-200005-I!!PDF-E.pdf )〕 for the frequency range of electromagnetic waves between 300 hertz and 3 kilohertz. In magnetosphere science and seismology, alternative definitions are usually given, including ranges from 1 mHz to 100 Hz,〔V.A. Pilipenko, "ULF waves on the ground and in space", Journal of Atmospheric and Terrestrial Physics, Volume 52, Issue 12, December 1990, Pages 1193-1209, ISSN 0021-9169, .〕 1 mHz to 1 Hz,〔T. Bösinger and S. L. Shalimov, "On ULF Signatures of Lightning Discharges", Space Science Reviews, Volume 137, Issue 1, Pages 521-532, June 2008, .〕 10 mHz to 10 Hz.〔O. Molchanov, A. Schekotov, E. Fedorov, G. Belyaev, and E. Gordeev, "(Preseismic ULF electromagnetic effect from observation at Kamchatka )", Natural Hazards and Earth System Sciences, Volume 3, Pages 203-209, 2003〕 Frequencies above 3 Hz in atmosphere science are usually assigned to the ELF range.
Many types of waves in the ULF frequency band can be observed in the magnetosphere and on the ground. These waves represent important physical processes in the near-Earth plasma environment. The speed of the ULF waves is often associated with the Alfvén velocity that depends on the ambient magnetic field and plasma mass density.
This band is used for communications in mines, as it can penetrate the earth.〔(HF and Lower Frequency Radiation - Introduction )〕
==Earthquakes==
Some monitoring stations have reported that earthquakes are sometimes preceded by a spike in ULF activity. A remarkable example of this occurred before the 1989 Loma Prieta earthquake in California, although a subsequent study indicates that this was little more than a sensor malfunction. On December 9, 2010, geoscientists announced that the DEMETER satellite observed a dramatic increase in ULF radio waves over Haiti in the month before the magnitude 7.0 Mw 2010 earthquake. Researchers are attempting to learn more about this correlation to find out whether this method can be used as part of an early warning system for earthquakes.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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