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| Titel |
ULF/ELF emissions observed in Japan, possibly associated with the Chi-Chi earthquake in Taiwan |
| VerfasserIn |
K. Ohta, K. Umeda, N. Watanabe, M. Hayakawa |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 1, no. 1/2 ; Nr. 1, no. 1/2, S.37-42 |
| Datensatznummer |
250000019
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| Publikation (Nr.) |
 copernicus.org/nhess-1-37-2001.pdf |
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| Zusammenfassung |
| ULF/ELF emission
observation has been performed at Nakatsugawa observatory (geographic
coordinates; 35.4° N, 137.5° E, Gifu prefecture) since January 1999. The
equipment consists of three-orthogonal magnetic sensors (induction coils),
amplifiers, A/D converters and the data logger with a computer. The
frequency range of observation is from 0.001 Hz to 50 Hz. The serious
changes in ELF magnetic field intensity were detected on 20 September
1999, in such a way that the ELF noise level is found to increase by more
than 5 dB from the normal level for about 1.5 h during 21:30–23:00
Japanese Standard Time on 20 September and also the upper limit extends up
to 50 Hz. A careful comparison with the nearby lightning as detected by
VLF, enables us to confirm that this abnormal ELF noise level increase is
not due to the nearby lightning. The phase difference of these ELF
emissions (BX , BY) was measured, and indicates that these ELF emissions
are linearly polarized, suggesting that they have propagated in the
subionospheric waveguide over long distances. This polarization result
enables us to perform goniometric direction finding and the result shows
that the main direction of these ULF/ELF emissions is toward Taiwan.
Hence, it is likely that such ULF/ELF emissions are associated with the
Chi-Chi earth-quake in Taiwan at 02:27 Japanese Standard Time on 21
September 1999 (M = 7.6; depth 11 km). |
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