Earth Planets Space, Vol. 63 (No. 7), pp. 869-873, 2011
Takashi Maruyama1, Takuya Tsugawa1, Hisao Kato1, Akinori Saito2, Yuichi Otsuka3, and Michi Nishioka3
1National Institute of Information and Communications Technology, 2-1 Nukuikita 4-chome, Koganei, Tokyo 184-8795, Japan
2Department of Geophysics, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
3Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
(Received April 8, 2011; Revised May 19, 2011; Accepted June 7, 2011; Online published September 27, 2011)
A strong earthquake with a magnitude of 9.0 occurred at 1446:23 JST on March 11, 2011, in Japan. Ionospheric disturbances were detected at 1500 JST at four ionosonde stations. An irregular distortion of echo trace was observed at Kokubunji, which is the nearest station to the epicenter and is 440 km from it. Multiple-cusp-type trace indicating extra stratification was observed at Wakkanai and Yamagawa, which are 870 and 1410 km away from the epicenter. A small wavy fluctuation was observed at Okinawa 1910 km away from the epicenter. The real height analysis of the ionograms showed a vertical structure with a scale size of 20∼30 km.
Key words: Ionospheric disturbance, earthquake, F1 cusp enhancement, intermediate layer, stratification.