Geomagnetic anomaly at Lunping before the 1999 Chi-Chi earthquake (M w = 7.6) in Taiwan

Kuang-Jung Chen (), Bonbbon Chiu, Jee-Shiang Wang, Cheng-Yu Lee, Cheng-Horng Lin and Kevin Chao

Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards, 2011, vol. 58, issue 3, 1233-1252

Abstract: A strong earthquake with a magnitude of 7.6 (M L = 7.3) occurred on September 21, 1999, in central Taiwan. In order to discern any potential precursors before this earthquake, geomagnetic data at Lunping (LNP), Taiwan, Geomagnetic Observatory situated 100 km from the epicenter are examined using two methods, i.e., the traditional induction arrows and complex demodulation. Our results show that the remarkable temporal variation of real induction arrows appear to be strong prior to the great earthquake over the previous 24 months. After the great earthquake, the magnitudes of induction arrows decreased to the normal (mean of 8 years) levels. In other words, the direction of real induction arrows of the periods 30 and 20 min rotated 85° and 40° anticlockwise, respectively, before the Chi-Chi earthquake and returned to mean direction of last 10 years after the earthquake. A horizontal source field model using the finite difference method for 3-D shows that the variation of the real induction arrows might be ascribed to the conductivity variation body, which is 5 km buried at the epicenter area of the Chi-Chi earthquake, changing its conductivity from 0.002S/m to 0.06 S/m. The ratios of modulus (demodulated by using the complex demodulation method) over a period 12, and 8 h relative to the period of 24 h reveal a remarkable change that appeared 4–5 months prior to this strong earthquake. They increased gradually from the beginning of 1999 to August 1999 and decreased again to a (8 years) mean level after the strong earthquake occurrence. We consider that the variation of the induction arrow might be ascribed to the conductivity anomaly, which is buried 5 km at the south-east side of LNP with a conductivity change of 0.06 S/m. We propose that this elevation might be related to the preparation process of the great earthquake. Copyright Springer Science+Business Media B.V. 2011

Keywords: Induction arrow; Geomagnetic field; Chi-Chi earthquake (search for similar items in EconPapers)
Date: 2011
References: View complete reference list from CitEc
Citations:

Downloads: (external link)
http://hdl.handle.net/10.1007/s11069-011-9726-7 (text/html)
Access to full text is restricted to subscribers.

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:spr:nathaz:v:58:y:2011:i:3:p:1233-1252

Ordering information: This journal article can be ordered from
http://www.springer.com/economics/journal/11069

DOI: 10.1007/s11069-011-9726-7

Access Statistics for this article

Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards is currently edited by Thomas Glade, Tad S. Murty and Vladimír Schenk

More articles in Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards from Springer, International Society for the Prevention and Mitigation of Natural Hazards
Bibliographic data for series maintained by Sonal Shukla () and Springer Nature Abstracting and Indexing ().