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| Titel |
ULF magnetic emissions connected with under sea bottom earthquakes |
| VerfasserIn |
V. S. Ismaguilov, Yu. A. Kopytenko, K. Hattori, P. M. Voronov, O. A. Molchanov, 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.23-31 |
| Datensatznummer |
250000017
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| Publikation (Nr.) |
 copernicus.org/nhess-1-23-2001.pdf |
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| Zusammenfassung |
| Measurements of ULF
electromagnetic disturbances were carried out in Japan before and during a
seismic active period (1 February 2000 to 26 July 2000). A network
consists of two groups of magnetic stations spaced apart at a distance of
≈140 km. Every group consists of three, 3-component high
sensitive magnetic stations arranged in a triangle and spaced apart at a
distance of 4–7 km. The results of the ULF magnetic field variation
analysis in a frequency range of F = 0.002–0.5 Hz in connection with
nearby earth-quakes are presented. Traditional Z/G ratios (Z is the
vertical component, G is the total horizontal component), magnetic
gradient vectors and phase velocities of ULF waves propagating along the
Earth’s surface were constructed in several frequency bands. It was
shown that variations of the R(F) = Z/G parameter have a different
character in three frequency ranges: F1 = 0.1 ± 0.005, F2 = 0.01 ± 0.005
and F3 = 0.005 ± 0.003 Hz. Ratio R(F3)/R(F1) sharply increases 1–3
days before strong seismic shocks. Defined in a frequency range of F2 =
0.01 ± 0.005 Hz during nighttime intervals (00:00–06:00 LT), the
amplitudes of Z and G component variations and the Z/G ratio started to
increase ≈ 1.5 months before the period of the seismic
activity. The ULF emissions of higher frequency ranges sharply increased
just after the seismic activity start. The magnetic gradient vectors (∇
B ≈ 1 – 5 pT/km), determined using horizontal
component data (G ≈ 0.03 – 0.06 nT) of the magnetic stations
of every group in the frequency range F = 0.05 ± 0.005 Hz, started to
point to the future center of the seismic activity just before the
seismoactive period; furthermore they continued following space
displacements of the seismic activity center. The phase velocity vectors
(V ≈ 20 km/s for F = 0.0067 Hz), determined using horizontal
component data, were directed from the seismic activity center. Gradient
vectors of the vertical component pointed to the closest seashore (known
as the "sea shore" effect). The location of the seismic activity
centers by two gradient vectors, constructed at every group of magnetic
stations, gives an ≈ 10 km error in this experiment. |
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