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| Titel |
Review of unprecedented ULF electromagnetic anomalous emissions possibly related to the Wenchuan MS = 8.0 earthquake, on 12 May 2008 |
| VerfasserIn |
M. Li, J. Lu, M. Parrot, H. Tan, Y. Chang, X. Zhang, Y. Wang |
| 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 ; 13, no. 2 ; Nr. 13, no. 2 (2013-02-08), S.279-286 |
| Datensatznummer |
250017567
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| Publikation (Nr.) |
 copernicus.org/nhess-13-279-2013.pdf |
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| Zusammenfassung |
| This work presents ground based ultra low frequency (ULF)
electromagnetic field measurements in the frequency range 0.1–10 Hz from
January 2007 to December 2008. In this time period a strong earthquake
series hits the Wenchuan region with a main shock of magnitude MS = 8.0
on 12 May 2008. The Hebei ULF electromagnetic observation network includes
eight observation stations in north China and the observation system named
E-EM is employed to record the electric potential difference between two
electrodes with an analog automatic real-time continuous pen recorder.
First, weak electric signals appeared on 11 October 2007 at Ningjin
station, most of which are with relative long periods ~0.4–3 s
and unequal amplitudes ~0.5–20 mm. Then, similar signals
appeared at Gaobeidian station at the end of October. Abnormal behavior with
various time intervals appeared randomly and not every day. At the beginning
of April 2008, one and a half months before the Wenchuan MS = 8.0 earthquake, the anomalies were gradually subject to an intensive
increase mainly in Gaobeidian SN direction and Ningjin EW direction. The
abnormal behavior appeared almost every day and the amplitudes of electric
signals, with short periods of ~0.1–0.3 s, enhanced to
~3–30 mm. Qingxian station started to record marginally high frequency
signals in SN and EW components in the middle of April. On 9 May, 3 days
before the main shock, the amplitude of high frequency information increased
sharply at the same time in two components at Gaobeidian station and the
maximum amplitude was up to 70 mm, i.e. 1.3 mV m−1 for the
electric field. This situation did not stop until 17 May, 5 days after the
main event. However, this kind of climax phenomena did not happen at Ningjin
station and Qingxian station. Then weak anomalous information lasted about
four months again, and strong signals appeared again for a short time before
several powerful aftershocks. It is the first time that an abnormity with so
large an amplitude and so long a duration time in the observation history of
this network though several strong earthquakes were recorded. Furthermore, no
obvious interferences have been found during this period. So this event is
possibly related to this shock although all these three stations are more
than 1300 km away from the Wenchuan earthquake epicenter. |
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