Observation by the Intercosmos-24 satellite of ELF-VLF electromagnetic emissions associated with earthquakes
Abstract
The measurements of emissions in the frequency range 8-20 kHz during 180 orbits of the Intercosmos-24 satellite from November 16, 1989 to December 31, 1989, are analyzed. Twenty-eight rather strong earthquakes (Ms between 5.2 and 6.1) took place during this period. The following findings have emerged from the analysis of these events. (1) Emissions in the two frequency bands with spectrum maxima at ULF-ELF (f less than 1000 Hz) and at VLF (f = 10-15 kHz) are typcially observed as bursts in the region nearly above the earthquake epicenter. (2) ULF-ELF emission spectrum intensity decreases with increasing frequency. (3) Only VLF emissions are observed far from the epicenter but near the appropriate L shell. (4) Emission occurrence probability is a maximum at 12-24 h before the main shock. Finally, the possible theoretical concepts are discussed in connection with the experimental results, and we suggest a plausible mechanism of precursory ELF and VLF emissions of earthquakes.
- Publication:
-
Annales Geophysicae
- Pub Date:
- May 1993
- Bibcode:
- 1993AnGeo..11..431M
- Keywords:
-
- Earthquakes;
- Electromagnetic Spectra;
- Emission Spectra;
- Intercosmos Satellites;
- Ionospheric Disturbances;
- Satellite Observation;
- Extremely Low Frequencies;
- Upper Atmosphere;
- Very Low Frequencies