Observation of Seismogenic Electromagnetic Phenomena and Recent Results
نویسنده
چکیده
近年地震に先行して発生する電磁気学的な現象が 様々な周波数帯において報告されている [1]~[3].これ らは,観測方法によって (a)地殻内部から出てくる電 磁波(自然放射)を直接観測する方法と (b)既存電波 の伝搬異常として地震に伴う現象を検出する方法(電 波サウンディング)とに大別される.前者は,地震の 発生準備段階において地殻内部で応力変化等の原因で 自然放射が発生するとの考えに立脚している.後者は, 地震に関連するじょう乱が大気圏や電離圏に発生する との仮説に基づく.もし伝搬経路上の大気圏や電離層 に異常があれば,精密に制御されて送信されている既 存電波の観測点での振幅や位相に異常が出現するとの 考えによる.地震電磁気現象が目指す地震の短期予知 の観点から注目されているのが,(1) 地圏内現象であ る ULF放射と (2)電離層じょう乱観測の二つである. (1)は (a)の直接放射のうちの極超低周波の電波であ る.(2)の観測には (b)の既存の VLF/LF送信局電波 の伝搬異常を用いている.本論文ではこれらの計測技 術と最新の成果や研究動向を紹介する.
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