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| Titel |
Application of polarization ellipse technique for analysis of ULF magnetic fields from two distant stations in Koyna-Warna seismoactive region, West India |
| VerfasserIn |
F. Dudkin, Rawat Gautam, B. R. Arora, V. Korepanov, O. Leontyeva, A. K. Sharma |
| 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 ; 10, no. 7 ; Nr. 10, no. 7 (2010-07-12), S.1513-1522 |
| Datensatznummer |
250008309
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| Publikation (Nr.) |
 copernicus.org/nhess-10-1513-2010.pdf |
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| Zusammenfassung |
A new approach is developed to find the source azimuth of the ultra low
frequency (ULF) electromagnetic (EM) signals believed to be emanating from
well defined seismic zone. The method is test applied on magnetic data
procured from the seismoactive region of Koyna-Warna, known for prolonged
reservoir triggered seismicity. Extremely low-noise, high-sensitivity
LEMI-30 search coil magnetometers were used to measure simultaneously the
vector magnetic field in the frequency range 0.001–32 Hz at two stations,
the one located within and another ~100 km away from the seismic
active zone. During the observation campaign extending from 15 March to 30 June
2006 two earthquakes (EQs) of magnitude (ML>4) occurred, which
are searched for the presence of precursory EM signals.
Comparison of polarization ellipses (PE) parameters formed by the magnetic
field components at the measurement stations, in select frequency bands,
allows discrimination of seismo-EM signals from the natural background ULF
signals of magnetospheric/ionospheric origin. The magnetic field components
corresponding to spectral bands dominated by seismo-EM fields define the PE
plane which at any instant contains the source of the EM fields.
Intersection lines of such defined PE planes for distant observation
stations clutter in to the source region. Approximating the magnetic-dipole
configuration for the source, the magnetic field components along the
intersection lines suggest that azimuth of the EM source align in the
NNW-SSE direction. This direction well coincides with the orientation of
nodal plane of normal fault plane mechanism for the two largest EQs recorded
during the campaign. More significantly the correspondence of this direction
with the tectonic controlled trend in local seismicity, it has been surmised
that high pressure fluid flow along the fault that facilitate EQs in the
region may also be the source mechanism for EM fields by electrokinetic
effect. |
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