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titleSeismo-ionospheric effects
Other Title電離層地効果
Author(jpn)恩藤 忠典
Author(eng)Ondo, Tadanori
Author Affiliation(jpn)宇宙地球環境研究所
Author Affiliation(eng)Space Earth Environment Laboratory
Issue Date1997-03-03
PublisherNational Space Development Agency of Japan (NASDA)
Publication titleInternational Workshop on Seismo Electromagnetics Abstracts
International Workshop on Seismo Electromagnetics Abstracts
Start page83
Publication date1997-03-03
AbstractGreat earthquake of magnitude 7.8 occurred near the Okushiri island off the Hokkaido southwest coast Japan, at 22:17 hours JST (Japan Standard Time) July 12, 1993. The ionospheric F2 layer critical frequency, f(sub 0)F2 decreased below the monthly median from three days before the earthquake onset to three days after it at Wakkanai and Kokubunnji, Japan and the ionospheric F-layer virtual height increased above the monthly median for three nights before the earthquake onset, and decreased below the monthly median after the onset at the above mentioned two stations. Since, according to local geomagnetic activities, the ionospheric disturbances were independent of solar-terrestrial disturbances, they were really coseismic effects. If the seismo earth current would induce a large-scale electric current system between the earth and ionosphere, an ionospheric Pedersen current could flow in the ionospheric E region. If an eastward or westward Pedersen current would flow in the northward geomagnetic field in the ionosphere, an upward or downward plasma movement could be caused by the vertical plasma drift in mid- and low-latitude ionosphere as observed by f(sub 0)F2 a h'F around the earthquake onset.
1993年7月12日JST(日本標準時)22時17分に北海道南東海岸沖の奥尻島付近でM7.8の大地震が発生した。電離層F2層の臨界周波数f(sub 0)F2は、稚内と国分寺において地震の開始の3日前から3日後まで月間中間値以下に減少し、電離層F層の実質高度は前述の2つの観測所において地震の開始3夜前に月間中間値以上に増加し、開始後は中間値以下に減少した。局所的な地磁気活動によれば、電離層擾乱は太陽-地球擾乱と独立なので、これらは実際に地震関連の効果である。これらは鉛直方向のプラズマ運動によりもたらされるものに違いない。もし地震地電流が地球と電離層の間に大規模電流系を作り出すとすると、電離層ペダーセン流が電離層E領域に流れるだろう。東向きまたは西向きのペダーセン電流が電離層の北向きの地球磁場に流入すると、地震発生の前後にf(sub 0)F2とh'Fで観測されたように、中・低緯度の電離層の垂直プラズマドリフトにより上方あるいは下方にへのプラズマ運動が生じるであろう。
Keywordsionospheric disturbance; seismic effect; F2 layer; critical frequency; plasma movement; plasma drift; seismo earth current; Pedersen current; 電離層擾乱; 地震効果; F2層; 臨界周波数; プラズマ運動; プラズマドリフト; 地震地電流; ペダーセン電流
Document TypeConference Paper
JAXA Category宇宙開発事業団

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