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Detailed Reference Information |
Henderson, T.R., Sonwalkar, V.S., Helliwell, R.A., Inan, U.S. and Fraser-Smith, A.C. (1993). A search for ELF/VLF emissions induced by earthquakes as observed in the ionosphere by the DE 2 satellite. Journal of Geophysical Research 98: doi: 10.1029/92JA01533. issn: 0148-0227. |
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Satellite observations of ELF/VLF wave activity by groups from both the Soviet Union and France have indicated the possibility of ELF/VLF radio emissions generated by earthquakes. However, an examination of ELF/VLF wave data from the low-altitude (apogee ~1300 km, perigee~300 km, inclination ~90¿) Dynamics Explorer 2 (DE 2) satellite showed no clearly distinguishable ELF/VLF signatures associated with earthquakes. After an initial survey of approximately 5000 DE 2 orbits, ELF and VLF wave data were selected from 63 satellite orbits, called earthquake orbits, in which the ionospheric footprint of the DE 2 crossed the geographic latitude while passing within ¿20¿ geographic longitude of the epicenters of imminent or recent earthquakes of magnitude ≥5.0. ELF/VLF noise measured near the epicenters was analyzed for occurrence rates and average spectra, as well as for peak and means electric field intensities in three spectrometers covering a frequency range of 4 Hz--512 kHz in 20 channels. The same analysis was then repeated for 61 carefully matched control orbits when there were no imminent or recent earthquakes within ¿20¿ geographic longitude or within ¿10¿ geographic latitude of the satellite footprint. These control orbits resembled the earthquake orbits with respect to latitude, longitude, local time, and geomagnetic index Kp. Sixty-three percent of the earthquake orbits showed an ELF or VLF emission above 10 &mgr; V/m in at least one of the 20 channels when the satellite passed near an epicenter. The same analysis performed on control orbit data yielded a 62% chance of observing similar emissions. Moreover, these results did not change when geomagnetic latitudes, instead of geographic latitudes, were considered. Further analysis failed to indicate any significant differences between ELF/VLF noise measured on earthquake orbits and control orbits with regard to the general nature of the spectra, the frequency of occurrence of emissions, and peak and mean values of the electric field of the emissions. ¿ American Geophysical Union 1993 |
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Abstract |
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Keywords
Seismology, Earthquake prediction, Seismology, Seismicity, Space Plasma Physics, Waves and instabilities |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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