 |
| Titel |
Variations of phase velocity and gradient values of ULF geomagnetic disturbances connected with the Izu strong earthquakes |
| VerfasserIn |
V. S. Ismaguilov, Yu. A. Kopytenko, K. Hattori, M. Hayakawa |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1561-8633
|
| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 3, no. 3/4 ; Nr. 3, no. 3/4, S.211-215 |
| Datensatznummer |
250000679
|
| Publikation (Nr.) |
 copernicus.org/nhess-3-211-2003.pdf |
|
|
|
|
|
| Zusammenfassung |
| Results of study of
anomaly behavior of amplitudes, phase velocities and gradients of ULF
electromagnetic disturbances (F = 0.002 – 0.5 Hz) before and during a
seismic active period are presented. Investigations were carried out in
Japan (Izu and Chiba peninsulas) by two groups of magnetic stations spaced
apart at a distance ~ 140 km. Every group (magnetic gradientometer)
consists of three 3-component high sensitive magnetic stations arranged in
a triangle and spaced apart at distance 4–7 km. Kakioka magnetic station
(>200 km to the North from Izu) was used as a reference point.
Available data (only night-time intervals 00:00–07:00 LT) were
preliminary filtrated by narrow pass-band filters (16 frequency bands –
periods T = 2–512 s). The amplitude, gradient and phase velocity values
and probabilities of directions of gradient and phase velocity vectors
were constructed for the every frequency band. Apparent resistivities of
the Earth’s crust in the every frequency band were calculated using the
phase velocity values. It was found that Z component amplitudes of the ULF
magnetic disturbances increased at Izu peninsula 2–4 weeks before the
seismic active period and 2–4 days before the strongest seismic shocks
(M > 6). Ratio of Z component amplitudes of Kamo (Izu) and Kakioka data
(Zk/Zkk) increased during 2–4 weeks before the
seismic activity start (27 June 2000) and reached a maximum just before a
moment of the strongest seismic shock (EQ with M = 6.4). The gradient and
the phase velocity values had an anomaly behavior during the same 2–4
weeks before the start of seismic active period. The gradient vectors of
the total horizontal component of the ULF magnetic pulsations were
probably directed to the regions with increased conductivity. New
additional direction of the gradient vectors appeared 2–3 weeks before
the seismic activity start – the direction to the seismic active area
which appeared due to a magma rising. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|