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www.nat-hazards-earth-syst-sci.net/8/573/2008/
doi:10.5194/nhess-8-573-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
On the ionospheric perturbation associated with the 2007 Niigata Chuetsu-oki earthquake, as seen from subionospheric VLF/LF network observations
1Department of Electronic Engineering and Research Station on Seismo Electromagnetics, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu Tokyo 182–8555, Japan
2Department of Electronic and Information Engineering, Chubu University, Kasugai Aichi, Japan
3Department of Physics, Kochi University, Kochi Kochi, Japan
Abstract. In order to investigate any precursory effect of ionospheric perturbations associated with the large 2007 Niigata Chuetsu-oki earthquake (16 July 2007) (magnitude, 6.8), we have made full use of our VLF/LF network observation in Japan by examing the four propagation paths; JJI transmitter (Kyusyu, Ebino)-MSR (Moshiri, Hokkaido), JJY transmitter (Fukushima)-MSR, JJY-KOC (Kochi) and JJI-CBA (Tateyama, Chiba). For the former two paths of JJI-MSR and JJY-MSR, we have observed significant propagation anomalies (both a decrease in nighttime average amplitude and an enhancement in nighttime amplitude fluctuation both satisfying the 2σ (σ: standard deviation) criteria) on 8–9 July, about one week before the earthquake. However, the lack of observation for the path from JJY-KOC, has enabled us to make no conclusion for this path. On the other hand, the path from JJI-CBA does not seem to be perturbed. Although this earthquake is very big and shallow, the amount of VLF anomaly for this earthquake is not so pronounced as expected, probably because the epicenter is not unfortunately located within the sensitive areas of any propagation paths. These observational facts suggest that the lower ionosphere above the epicenter is perturbed definitely prior to the earthquake, with radius of a few hundred kilometers.
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Citation: Hayakawa, M., Horie, T., Yoshida, M., Kasahara, Y., Muto, F., Ohta, K., and Nakamura, T.: On the ionospheric perturbation associated with the 2007 Niigata Chuetsu-oki earthquake, as seen from subionospheric VLF/LF network observations, Nat. Hazards Earth Syst. Sci., 8, 573-576, doi:10.5194/nhess-8-573-2008, 2008. Bibtex EndNote Reference Manager XML
