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| Titel |
Scaling characteristics of ULF geomagnetic fields at the Guam seismoactive area and their dynamics in relation to the earthquake |
| VerfasserIn |
N. Smirnova, M. Hayakawa, K. Gotoh, D. Volobuev |
| 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. 3 ; Nr. 1, no. 3, S.119-126 |
| Datensatznummer |
250000178
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| Publikation (Nr.) |
 copernicus.org/nhess-1-119-2001.pdf |
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| Zusammenfassung |
| The long-term
evolution of scaling (fractal) characteristics of the ULF geomagnetic
fields in the seismoactive region of the Guam Island is studied in
relation to the strong (Ms = 8.0) nearby earthquake of 8 August 1993. The
selected period covers 10 months before and 10 months after the
earthquake. The FFT procedure, Burlaga-Klein approach and Higuchi method,
have been applied to calculate the scaling exponents and fractal
dimensions of the ULF time series. It is found that the spectrum of ULF
emissions exhibits, on average, a power law behaviour S(f ) α
f -b , which is a
fingerprint of the typical fractal (self-affine) time series. The spectrum
slope b fluctuates
quasi-periodically during the course of time in a range of b
= 2.5–0.7, which corresponds to the fractional Brownian motion with both
persistent and antipersistent behaviour. An tendency is also found for the
spectrum slope to decrease gradually when approaching the earthquake date.
Such a tendency manifests itself at all local times, showing a gradual
evolution of the structure of the ULF noise to a typical flicker noise
structure in proximity to the large earthquake event. We suggest
considering such a peculiarity as an earthquake precursory signature. One
more effect related to the earthquake is revealed: the longest
quasi-period, which is 27 days, disappeared from the variations of the ULF
emission spectrum slope during the earthquake, and it reappeared three
months after the event. Physical interpretation of the peculiarities
revealed has been done on the basis of the SOC (self-organized
criticality) concept. |
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