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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Poster presentation 2057
Ionospheric anomalous changes observed by GPS-TEC and NmF2 possibly
associated with large earthquakes
Mr. Masahide Nishihashi
Graduate Course of Science Chiba University IASPEI
Hau-Kun Jhuang, Katsumi Hattori, Jann-Yenq Liu, Sarmoko Saroso, Djedi S.
Widarto
A lot of anomalous electromagnetic phenomena possibly associated with large earthquakes have been
reported. Recently, scientistsfound an apparent reduction in GPS-TEC values occurred within 1 5 days
prior to M ≥ 6.0 earthquakes in Taiwan. However, those recent studies were not cross-checked by
simultaneous data sets observed at other places to confirm the ionospheric anomalies being earthquake
related. In this study, we retrieved GPS-TEC records, routinely published in the global ionosphere maps
(GIM). Simultaneous data in various other locations outside of Taiwan are examined to see whether the
anomalies observed in Taiwan before the 1999 Chi-Chi earthquake (Mw7.6) and Chia-Yi earthquake
(M6.4) are local or global effects. The result shows that the anomalies in Taiwan three days before the
Chi-Chi earthquake (18 September), and one and three days before the Chia-Yi earthquake (19 and 21
October) are local phenomena. It means that the ionospheric-disturbed areas were localized around
Taiwan, and did not spread all the way to Tokyo in Japan. We conclude that the disturbed areas are at
least less than about 2200km in radius and may be much smaller. We also obtained similar tendency in
the case of the 2004 Sumatra-Andaman earthquake (M9.0).
Keywords: gps tec, nmf2, ionospheric disturbances